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Cdopt6 de-s couleuirs-Ceiitd di colore.


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COLOR-BLINDNESS:
ITS DANGERS AND ITS DETECTION.
BY
B. JOY JEFFRIES, A.M., M.D.,
(HARVARD,)
Fellow of the Massachusetts Medical Society; Ophthalmic Surgeon Massachusetts
Charitable Eye and Ear Infirmary, Carney Hospital, and New-England Hospital
for Women and Children; Member of the International Periodic Congress of
Ophthalmology, American Ophthalmological Society, Boston Society
of Medical Sciences, Boston Society for Medical Observation,
Boston Society of Natural History, &c.


BOSTON:
HOUGHTON, OSGOOD AND COMPANY.
Qtb e Berlih t preu, 0ambri'ge.
1879.




COPYRIGHT, 1879,
BY B. JOY JEFFRIES.
All rights reserved.
C. 7. Peters & Son, Stereotypers,
73 Federal Street.




TO
FRITHIOF HOLMGREN, M.D.,
PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF
UPSALA, SWEDEN,
THIS VOLUME
IS RESPECTFULLY DEDICATED.




"Why should we look one common faith to find,
Where one in every score is color-blind?
If here on earth they know not red from green,
Will they see better into things unseen?"
DR. 0. W. HOLMES: Andover Poem, June, 1878.




CONTENTS.
PAGE
PREFACE......... vii-xiii
INTRODUCTION....... xv-xvi
CHAPTER
I. HISTORICAL CASES OF COLOR-BLINDNESS.  1 -II. COLOR-BLIND MISTAKES....    7-21
III. FORMER CLASSIFICATION OF THE COLOR-BLIND 22-25
IV. PRESENT CLASSIFICATION OF THE COLOR-BLIND
IN ACCOBDANCE WITH THE YOUNG-HELMHOLTZ
THEORY OF COLOR-PERCEPTION..  26-41
V. PRECISE CONDITION OF THE VISION OF THE COLOR-BLIND..                    42-47
VI. COLOR-BLINDNESS FROM DISEASE OR INJURY, 48-53
VII. COLOR-BLINDNESS HEREDITARY..   4-63
VIII. PHYSICAL PECULIARITIES CONNECTED WITH
COLOR-BLINDNESS....6468
IX. FREQUENCY OF COLOR-BLINDNESS IN MALES,  69-79
X. INFREQUENCY OF COLOR-BLINDNESS IN FEMALES........  80-87
XI. CONCEALMENT OF COLOR-BLINDNESS IN PRACTICAL LIFE....... 88-110
XII. INCURABILITY OF CONGENITAL COLOR-BLINDNESS........ 111-124
XIII. PALLIATION OF CONGENITAL COLOR- BLINDNESS........ 125-136
XIV. DANGERS ARISING FROM COLOR-BLINDNESS ON
RAILROADS. CONDITION OF COLOR - BLIND
EMPLOYES...... 137-160
V




Vi                 CONTENTS.
CHAPTER                                      PAGE
XV. DANGERS FROM COLOR - BLINDNESS ON THE
OCEAN....... 161-165
XVI. CAN THE RAILROAD AND MARINE SIGNALS
BE CHANGED?...... 166-175
XVII. NECESSITY AND DIFFICULTY OF CONTROL, 176-181
XVIII. METHODS OF TESTING\ FOR COLOR -BLINDNESS........ 182-195
XIX. IHOLMGREN'S METHOD OF DETECTING COLORBLINDNESS, AS DESCRIBED IN HIS ORIGINAL
WORK.-EXAMINATION AND DIAGNOSIS, 196-220
XX. SPECIAL DIRECTIONS FOR CONDUCTING THE
TEST........ 221-236
XXI. EFFORTS TO CONCEAL OR TO FEIGN COLORBLINDNESS...... 237-240
XXII. METHOD OF DECIDING THE PRECISE AMOUNT
OF COLOR-BLINDNESS BY PROFESSOR HOLMGREN'S CHROMATOSKIAMETER, OR COLORSENSE TESTER. - PROFESSOR DONDERS'S
METHOD OF DETERMINING QUANTITATIVE
COLOR-PERCEPTION..... 241-250
XXIII. LAWS OF CONTROL OF COLOR-BLINDNESS NOW
IN FORCE IN EUROPE. -LEGISLATIVE ACTION OF THE STATE OF MASSACHUSETTS, 251-280
XXIV. PERSONAL EXPERIENCE WITH     HOLMGREN'S
METHOD.- SUGGESTIONS AS TO ITS USE, 281-286
XXV. CONCLUSIONS AND RECAPITULATION. 287-289
BIBLIOGRAPHY...... 291-308




PREFACE.


I HAVE dedicated this volume to my friend Professor
Holmgren, because I consider that to him above all
others do we owe the present and future control of
color-blindness on land and sea, by which life and
property are safer, and the risks of travelling less.
To his Majesty the King of Sweden are due the
thanks of all for his personal interest in the investigation of color-blindness, and his practical good sense in
immediately putting into execution the plans and proposals of Professor Holmgren, by which the subject
was so prominently brought forward as to command the
attention and example of other nations.  It is earnestly hoped that this country will follow rapid suit.
Professor Holmgren's book on "Color-Blindness and
its Relations to Railroads and the Marine " was published in Swedish, in 1877, at Upsala. Immediately
after this a French translation was printed, which soon
called very general attention to his labors and their
results. An authorized translation into German appeared last year (1878). I had agreed with him to
translate the work into English, when an abridged translation appeared from the Reports of the Smithsonian
vii




viii


PREFACE.


Institute at Washington. This, of course, prevented
any publisher from being willing to risk a complete
translation. The very necessary explanatory colored
plate was not given in the Smithsonian translation. I
understand that it will be in an extra edition. This
English translation is so abridged as to greatly interfere with its value and its practical use.
Had, however, I been enabled to reproduce Professor
Holmgren's book entire, I am afraid it would not have
accomplished its purpose so well in this country as in
Europe, from the general lower tone of scientific knowledge on the part of those for whom it was especially
written, and also the lack of just the persons -namely,
the railroad-surgeons-who could make immediate application of the method for detecting color-blindness,
and have convinced the authorities of its necessity.
Aside, also, from the difficulties of publication, I found
that a simple translation was not likely to be so generally read.
To bring before the community the dangers and the
prevalence of color-blindness, I thought it best to
prosecute my researches amongst the places of learning and teaching. Hence I chose our immediate universities, colleges, and public schools. Thus, whilst I
was pursuing my own individual studies of color-blindness, I was at the same time gathering the necessary statistics in proof of the position I took, and disseminating
a knowledge of the whole subject, very especially the
important one of its frequency. It is rather curious
that this volume is only the third monograph in bookform on this subject. Professor Wilson of Edinburgh
published in 1855 a small book, being a collection of
his several articles on this subject. Yet the literature
of normal and abnormal chromatic power is pretty ex



PREFACE.


ixS


tensive, as may be seen by the bibliography appended
to this volume. I first publicly discussed the subject
before the Boston Society of Natural History, March
7, 1877. An article of mine on the "Dangers from
Color-Blindness in Railroad Employes and Pilots " was
printed in the Ninth Annual Report of the Massachusetts State Board of Health, 1878. April 8, 1878,
I gave a lecture on color-blindness before the Society
of Arts of the Institute of Technology in Boston.
Feb. 23, 1878, I read a paper on the " Incurability of
Congenital Color-Blindness " before the Suffolk District
Medical Society in Boston, published in " The Boston
Medical and Surgical Journal" March 28, 1878. May
25, 1878, I read a paper on the "I Relative Frequency of
Color-Blindness in Males and Females " at the Suffolk
District Medical Society, and also at the July meeting
at Newport of the American Ophthalmological Society;
published, July 26, in "I The Boston Medical and Surgical Journal." The substance of these papers is included in this volume. I have quoted largely from
Professor Wilson's book, not only because it is quite
out of print, but also because the cases he relates are
interesting as being in England, and his deductions are
truthful and valuable, although much of the theory
presented is now old to science. I have given a good
part of Professor Holmgren's book, including what is
essential to be known and understood by our railroad
authorities and the specialists they must employ in
carrying out any system of thorough examinations.
The explanations and directions may seem to many
unnecessarily minute, and the description too extended;
but these are especially intended for examiners, who,
I think, when using this test, will thank me for putting
them within their easy reach.




X


PREFACE.


The importance of this whole question of color-blindness I need not insist on here. " The Railroad Gazette " of Jan. 24, 1879, after discussing the 740 accidents by which 204 people were killed and 756 injured,
says, " What most needs doing now is the improvement of the men who work the roads, - officers and
employes, - though there is still plenty of room for
progress in the tools with which they work."
I have not in this volume entered into the loss of
time and money from color-blindness in the great industries where a perfect chromatic sense is needed; or the
mortifications, &c., arising from constant mistakes of
dress &c., in every-day life, -as all these bear no relation to the importance of the danger to life and property on land and sea from this curious visual defect.
The railroads of England pay two million dollars a
year for killed and injured travellers.
I must explain some expressions in my text. I
always use the term color-blindness, instead of Daltonism, as more truthfully representing the defect in general, as Dalton was red-blind; and also in order not to
continue to attach this defect to his name. This has
become pretty universal, except with the French, who,
having no one word for color-blindness, still say Daltonisme for brevity's sake. My speaking of a colorblind I would apologize for by saying, were I to have
added " person " each time, my readers would, I think,
have preferred the present bad grammar.
I am quite aware, that, instead of presenting the material of this volume in its present shape, I could have
given a condensed essay on color-blindness more easily
read; but such a book would not meet the wants of the
immediate future. The question of color-blindness is
soon coming up in a very practical form in this coun



PREPAYE


xti


try. Those who have to deal with it will properly ask
for the original material which they may themselves
study, and which I have here collected. Such material,
as my bibliography shows, is widely scattered and in
foreign languages; whilst other I here present has never
been published. For this reason I risk the natural criticism my work will call forth, rather than fail to give
full opportunity for those who from their position must
hereafter have my gathered material within their reach.
As this volume is intended to meet the wants of several quite different classes in the community, its contents are somewhat varied. Many of the chapters may
be read by themselves, by those who are only interested
in the subject from the point of view touched on in that
special chapter. General readers will find the historical cases, and the curious mistakes caused by this
chromatic defect, of most interest to them perhaps.
Physicians will be interested in facts relating to colorblindness from disease, its heredity, and the. supposed
peculiarities heretofore connected with it, as also its incurability. Scientists and physiologists will naturally
turn to the accounts of the precise condition of colorblindness and its relation to normal color-sense, as well
as the additional methods of detection. The color-blind
cannot but be interested in the palliatives of congenital
color-blindness, since we can now do more for them than
formerly. The dangers on land and sea concern us all.
Railroad authorities will find full explanation of the
precise condition of their color-blind employ6s. The
possible change of railroad and marine signals will also
concern them and the officers of the navy and mercantile marine. The possibility of detecting and eliminating the color-blind is important to those whose position
requires them to avoid employing such. The methods




xii


PREFACE.


of so doing interest the specialists employed for this
purpose. Our national and state legislatures and railroad commissioners will naturally turn to the account
of the present provisional European laws in reference
to the control of color-blindness on land and sea.
I have hitherto avoided seeking for the color-blind,
and discouraged those who I understood would apply
to me; because I desired to have my statistics as near
as possible precisely represent the truth as to the prevalence of this chromatic defect. MAy present numbers
are so large as to perfectly decide, for myself at least,
this point. I therefore am now anxious to hear from
the color-blind, by letter or otherwise, as each and
every account is of value. The personal observations
of any who have this defect would interest me, and be
of service to science. All names would of course be
strictly confidential. I am at present devoting special
attention to the question of heredity, and naturally very
anxious to hear from any one on this point. In many
color-blind families the facts must be pretty well known
as to the different members, and such I desire to have
causa scientice. My professional brethren may be able
to assist me in this, and I would hereby ask it of them.
I well know that many color-blind persons, whilst
shrinking from exhibiting their defect, would not hesitate to give an account of their case when assured
their names would not be used.
The dedication of this volume, and the free use I
have made of his material, show how much I am indebted to Professor Holmgren of Upsala, Sweden, with
whom I have been in constant communication. I have
also to greatly thank Professor Donders of Utrecht for
advice and suggestions, as well as for the rules of the
Holland railroads. I am indebted for information and




PREFACE.


MUi


numerous publications to the following gentlemen,
whom I would hereby gratefully remember: Dr. Magnus of Breslau, Drs. Eulenberg and Hirschberg of Berlin, Dr. Stilling of Cassel, Dr. Cohn of Breslau, Dr.
Zehender of Rostock, Dr. Schiess of Basle, Dr. Warlomont of Brussels, Professor Delboeuf of Lille, Drs.
Favre and Dor of Lyons, Dr. Nicati of Marseilles, Dr.
Quaglino of Pavia, Dr. Daae of Kragero, Norway, and
Dr. HIjort of Christiana, Norway, Dr. A. von Reuss
of Vienna, Dr. Robertson of Edinburgh, and Mr. S.
Wright Dunning of I The Railroad Gazette" of New
York.
To the Boston School Board my thanks are specially
due for permission to test the scholars of the public
schools, in which work I am still engaged.
To avoid cumbering this volume with references, I
use an author's name, and the bibliography will enable
the reader to turn to the original. There is, I believe,
no excuse for a writer not giving his best work to the
public; but I must add here, that the time for my
eighteen thousand examinations for color-blindness,
and the preparation of this volume, has been stolen
from the busy hours of a professional life.
B. JOY JEFFUIES, M.D.
15 CHESTNUT STREET, 13BACON HILL, BOSTON.








INTRODUCTION.
THERE are some points in reference to color-perception which I must first explain to my unprofessional
readers, to show what color-blindness is not. Our
point of best vision on the retina is directly in the
centre, and over but a small space here; so that, to
see an object distinctly, we must carefully turn the eye,
to keep the picture on this portion. In looking at a
long word on a page, we unconsciously travel along it
to catch all the letters. If we keep our eye fixed on
one point, and move a letter away from this point, its
form is soon lost, and we fail to recognize it. In other
words, if the image of the letter falls on the retina but
a little way from the centre, called " the yellow spot"
from its color, it is confused. Form-perception diminishes very rapidly from the centre outwards in all directions. Now, this is also the case in reference to color.
Let one eye be closed, and the other fixed on a brightred object, like a wafer, held before it. When moved
gradually out from the central field of vision, the wafer
will decrease in brightness, and finally appear black.
Its form we may still discern. This is not color-blindness. A painter has added a bright little scarlet flower
xv




Xvi


INTRODUCTION.


down in one corner of his picture, and turns to work in
the centre, when suddenly the scarlet flower loses its
color, because its image falls far away on the retina
from the point of best color-perception. This same
will be found in reference to the other primary colors
in varying degrees.
Another point: Whenever the retina is tired out
with one color, it can only perceive the complementary
one. If with one eye we gaze steadily for some seconds at a bright-green disk on a white ground, and then
quickly look at another white surface, we shall see a
red disk. Gazing fixedly at the setting sun when a
deep red, and turning quickly to the east, we shall see
a rising green sun. I hardly need say this also is not
color-blindness.
Again: the crystalline lens in the eye becomes, with
age, harder, and of a yellowish color, - up to positive
blackness. When opaque, it prevents, of course, the
passage of light through the pupil: it is called cataract. This opaque lens we then remove from the eye,
and replace it by a strong convex lens in the spectacles. Whilst the lens has been turning yellow, all the
person's light has been yellow; so that, when the lens
is removed, the impression will be that of the complementary color, -bluish. Many old persons whom I
have operated on for cataract, after it was removed,
and they were able to use their sight, complained that
every thing was blue; that, for instance, their children's faces appeared blue: and they naturally often
expressed considerable disappointment that life was to
be to them wholly bluish. This is not true color-blindness, and soon wears off. Santonine,. or worm-seed,
causes, when taken, all objects to appear a bright yellow, or sometimes its complementary color, violet.




INTRODUCTION.              Xv11
The effect is not permanent, and passes off in a few
hours.
Another physiological fact in relation to color-perception is very important, and seems to be generally
quite unknown or neglected. Around the point of best
vision in the centre of the retina is a zone where we
perceive all of the three so-called base colors, -red,
green, and violet. Outside of this there is another
zone, in which we have a perception of only two;
namely, green and violet; and again, beyond this, on
the retina, only blue or violet is perceived. We shall
hereafter see how these zones resemble color-blindness.








EXPLANATION OF THE COLORED PLATE.
REPEATED and inexcusable mistakes have been made in
Europe in reference to this colored plate of Prof. Holmgren.
It has been spoken of as if intended to be used to test for
color-blindness, and has also been so used. But, as he expressly states, it is only intended to illustrate the characteristic
mistakes of the color-blind, and the colors of the sample
worsteds to be employed.
I. TiHE GBEEN TEST.
If the person examined takes any of the confusion-colors (1
to 5) to put with the green, he proves himself color-blind; or
even if he seems to want to put them together.
II. a. THE PURPLE TEST. (This contains Red and Violet.)
The color-blind puts with it the colors 6 to 7, always a
deeper color.
If he puts only purple colors, he is incompletely color-blind.
If he takes blue or violet, like 6 and 7, or both, either with
or without purple, he is completely red-blind.
If he takes green or gray, like 8 and 9, or one alone, with or
without purple, he is completely green-blind.
II. b. THE RED TEST. (Not necessary to be used.)
Here the red-blind puts, with the red, dark green and brown
(10 and 11), which are much darker than the test.
The green-blind puts, with the red, lighter green and brown
than the test.
The violet-blind matches, with the purple, red, orange, and
purple.
XiX








COLOR-BLINDNESS:


ITS DANGERS AND ITS DETECTION.
CHAPTER I.
HISTORICAL CASES OF COLOR-BLINDNESS.
THERE seems no good reason to doubt that
color-blindness has existed at all times in man.
It is therefore certainly very curious that its detection, and consequent mention in literature, is
so very recent. A case of Dr. Tuberville's (1684)
has been quoted and referred to as one of colorblindness. In a letter to the Royal Society, London, Aug. 4, 1684, he says, "A maid two and
twenty years old came to me from Banbury, who
could see very well, but no color beside black and
white. She had such scintillations by night (with
the appearances of bulls, bears, &c.) as terrified
her very much. She could see to read sometimes
in the greatest darkness for almost a quarter of an
hour."
This is too indefinite to be admitted as a case
of color-blindness recognized at that date. We
probably shall hunt literature in vain for mention
of color-blindness till nearly a hundred years later,
1




2


COLOR-BLINDNESS:


when we come (in 1777) to Mr. Huddart's account
of the shoemaker Harris of Maryport, in Cumberland, Eng. This case is historic, and the description perfect in its way, rendering it quite worthy
of being given here in full. Huddart writes to
Rev. J. Priestley,"I have known Harris ten years, and had frequent opportunities of conversing with him. I had often heard from
others that he could discern the form and magnitude of all
objects very distinctly, but could not distinguish colors.
This report having excited my curiosity, I conversed with
him frequently on the subject. The account he gave was
this: that he had reason to believe other persons saw something in objects which he could not see; that their language
seemed to mark qualities with confidence and precision
which he could only guess at with hesitation, and frequently
with error. His first suspicion of this arose when he was
about four years old. Having by accident found in the
street a child's stocking, he carried it to a neighboring house
to inquire for the owner. He observed the people called it a
red stocking, though he did not understand why they gave
it that denomination, as he himself thought it completely
described by being called a stocking. The circumstance,
however, remained in his memory, and, together with subsequent observations, led him to the knowledge of his defect. As the idea of color is among the first that enters the
mind, it may perhaps seem extraordinary that he did not
observe his want of it still earlier. This, however, may in
some measure be accounted for from the circumstance of
his family being Quakers, among whom a general uniformity of colors is known to prevail. He observed, also, that,
when young, other children could discern cherries on a tree
by some pretended difference of color, though he could only
distinguish them from the leaves by their difference of size
and shape. He observed, also, that, by means of this difference of color, they could see the cherries at a greater distance than he could, though he could see other objects at as
great distance as they; that is, where the sight was not
assisted by the color. Large objects he could see as well as




ITS DANGERS AND ITS DETECTION.


8


other persons; and even the smaller ones, if they were not
enveloped in other things, as in the case of cherries among
the leaves. I believe he could never do more than guess
the name of any color; yet he could distinguish white from
black, or black from any light or bright color. Dove or
straw color he called white, and different colors he frequently called by the same name; yet he could discern a difference between them when placed together. In general, colors
of an equal degree of brightness, however they might otherwise differ, he frequently confounded together; yet a striped
ribbon he could distinguish from a plain one, but he could
not tell what the colors were with any tolerable exactness.
Dark colors in general he often mistook for black, but never
imagined white to be a dark color, nor dark to be a white
color. He was an intelligent man, and very desirous of
understanding the nature of light and colors, for which end
he had attended a course of lectures in natural philosophy.
He had two brothers in the same circumstances as to sight,
and two other brothers and sisters, who, as well as their
parents, had nothing of this defect. One brother is master
of a trading-vessel. I met him, and asked him whether he
had ever seen a rainbow. He replied he had often, and
could distinguish the different colors; meaning only that it
was composed of different colors, for he could not tell what
they were. A piece of ribbon he without difficulty pronounced striped, and not plain. The several stripes of white
he uniformly so called. The four black stripes he was deceived in; for three of them he thought brown, though they
were exactly of the same shade with the other, which he
properly called black. The light green he called yellow,
but he was not very positive. He said, 'I think that is
what you call yellow.' The middle stripe, which had a
slight tinge of red, he called a sort of blue. But he was
most of all deceived by the orange color: of this he spoke
very confidently, saying, ' This is the color of grass: this is
green.' I also showed him a great variety of ribbons, the
color of which he sometimes named rightly, and sometimes
as differently as possible from the true colors. These experiments were made in the daytime, and in a good light.
I asked him whether he imagined it possible for all the
various colors he saw to be mere difference of light and




4


COLOR-BLINDNESS:


shade; whether he thought they could be various degrees
between white and black, and that all colors could be composed of these two mixtures only. With some hesitation he
replied, No: he did imagine there was some other difference."
In 1779 Mr. J. Scott reported his own case in a
letter to Rev. Mr. Whisson, Trinity College, and
communicated by the Rev. Michael Lort. He
says that a full red and full green, pale blue and
pink, deep red and blue gave him the same sensation; but he readily distinguished yellow and
deep blue. The claret color of a garment seemed
to him deep black.
We must again seek in vain in literature for
cases of color-blindness till we come, in 1794, to the
English chemist Dalton's description of his own vision. His report excited so much attention, that
his name became attached to this chromatic defect,
which, by general consent, is now among nearly
all nations called color-blindness, not only from a
desire not to connect so distinguished a man's
name as Dalton with a physical defect, but as also
being nearer the truth, since only the red-blind
are Daltonians. Dalton's case is as interesting
as historical. He says, -
"It has been observed that our ideas of colors, sounds,
tastes, &c., excited by the same object, may be very different in themselves without our being aware of it, and that we
may nevertheless converse intelligibly concerning such objects as if we were certain the impressions made by them on
our minds were exactly similar. It will, however, scarcely
be supposed that any two objects, which are every day before
us, should appear hardly distinguishable to one person, and
very different to another, without the circumstance immediately suggesting a difference in their faculties of vision; yet
such is the fact, not only with regard to myself, but to many




ITS DANGERS AND ITS DETECTION.


5


others also. Notwithstanding the occasional study of
botany, I was never convinced of a peculiarity in my vision
till I accidentally observed the color of the flower Geranium
zonale by candle-light in 1792. The flower was pink, but
it appeared to me almost an exact sky-blue by day. In candle-light, however, it was astonishingly changed, not having
then any blue in it, but being what I called red, - a color
which forms a striking contrast to blue. Friends, when
asked, all agreed that the color was not materially different
from what it was by daylight, except my brother, who saw
it in the same light as myself. Two years afterwards I
commenced an investigation of the subject, assisted by a
friend, My observation began with the solar spectrum, or
colored image of the sun, exhibited in a dark room by means
of a glass prism. I found that persons in general distinguish
six kinds of color in the solar image; namely, red, orange,
yellow, green, blue, purple. To me it is quite otherwise: I
see only two, or at most three, distinctions. These I should
call yellow and blue, or yellow, blue, and purple. My yellow
comprehends the red, orange, yellow, and green of others; and
my blue and purple coincide wvith theirs. That part of the
image which others call red appears to me little more than
a shade, or defect of light; after that, the orange, yellow,
and green seem one color, which descends pretty uniformly
from anl intense to a rare yellow, making what I should call
different shades of yellow. The difference between the
green part and the blue part is very striking to my eye: they
seem to be strongly contrasted. That between the blue and
purple is much less so. The purple appears to be blue much
darkened and condensed."
The next cases reported in order of time are by
Dr. Nicholl, 1816 and 1818. One was * a boy
eleven years old, who was color-blind, like Dalton.
The other was a man aged forty-nine, who reported
thus:
" The color I am most at a loss with is green; and, in
attempting to distinguish it firom red, it is nearly guesswork. Scarlet in most cases I can distinguish, but a dark
bottle-green I could not, with any certainty, from brown.




6              COLOR-BLINDNESS:
Light yellow I know; dark yellow I might confound with
light brown, though in most cases, I think, I should know
them from red. The different shades of red and green, I
know not to which they belong; but, when they are before
me, I see a difference in the shade. Though I see different
shades in looking at a rainbow, I should say it was a mixture of yellow and blue, -yellow in the centre, and blue
towards the edges."
These cases are about all which may be properly
considered historic. I have referred to the original accounts, and quoted from them. It may be
noticed that mention of what the several persons
called colors -i.e., the names they gave them on
presentation -has been generally omitted. The
reason of this will be seen later. It need only
here be remarked, that asking the examined to
name colors is in reality no test of their colorperception; and, where this alone has been done,
their color-blindness cannot be accepted as proved.




ITS DANGERS AND ITS DETECTION.


7


CHAPTER II.
COLOR-BLIND MISTAKES.
IT will be interesting to note what mistakes
their chromatic deficiency causes the color-blind
to make, and therefore well worth our while to
listen to their own report, as well as that of their
examiners. Not only shall we find it curious and
interesting, but from a long series of cases we may
able to deduce, as has been done, some general
laws and classification of this peculiar visual condition. Commencing with the cases I have referred
to as historical: Dalton said the color of a florid
complexion seemed dull, opaque, blackish blue
upon a white ground. Diluted black ink on white
paper gives a color much resembling a florid complexion. It has no resemblance to the color of
blood. Blood appeared not unlike that color called
bottle-green. Grass appeared a very little different from red. The face of a laurel-leaf is a good
match to a stick of red sealing-wax, and the back
of the leaf answers to the lighter red of wafers.
Green woollen cloth-such as is used to cover
tables - appeared a dull brownish-red color. A
mixture of two parts mud and one red would come




8


COLOR-BLINDNESS:


near it. It resembled a red soil just turned up by
the plough. "When this kind of cloth loses its
color, as other people say, and turns yellow, then
it appears to me a pleasant green. Very lightgreen paper, silk, &c., is white to me." Blue was
the same to him as to other people, both by daylight and   candle-light.  "Colors appear to     me
much the same by moonlight as they do by candle-light. By lightning and the electric light they
appear as by daylight. A light-drab woollen cloth
seems to resemble a light green by day. My idea
of brown I obtain from a piece of white paper
heated almost to ignition. This color by daylight
seems to have a great affinity to green. Browns
seem to me very diversified: some I should call red.
Dark-brown woollen cloth I should call black."
A most amusing account was given by Babbage
of the incidents attending the presentation of Dalton at court: -
"Firstly he was a Quaker, and would not wear the
sword, which is an indispensable appendage of ordinary
court-dress. Secondly, the robe of a doctor of civil laws
was known to be objectionable on account of its color,scarlet, - one forbidden to Quakers. Luckily it was recollected that Dalton was afflicted with the peculiar colorblindness which bears his name, and that, as the cherries
and the leaves of a cherry-tree were to him of the same
color, the scarlet gown would present to him no extraordinary appearance. So perfect, indeed, was the color-blindness, that this most modest and simple of men, after having
received the doctor's gown at Oxford, actually wore it for
several days in happy unconsciousness of the effect he produced on the street." - Scientific London, 1874, p. 38.
Professor'Whewell reports having asked Dalton
what the bright-scarlet gown which he wore




ITS DANGERS AND ITS DETECTION.


9


resembled, and he pointed to some of the evergreens outside of the window, and said, that to his
eye their colors were quite alike. On the other
hand, the lining of the gown, which was pink silk,
he could not distinguish from sky-blue.
The first case recdrded -Harris the shoemaker
-noticed, when an infant, what the color-blind
nearly always do, namely, the inability to distinguish any red fruits from the surrounding green
leaves.   Recognition of their chromatic defect
dates not infrequently from companions being able
to pick strawberries, cherries, &c., more quickly.
One of Dr. Colquhoun's patients says,"I cannot perceive a bit of red sealing-wax if thrown
down'upon the grass, nor a piece of scarlet cloth hung upon
a hedge, which, I was told, was to be seen a mile off. I
once gathered some lichen, as a great curiosity, from the roof
of a friend's fishing-house. I thought it was of a bright
scarlet, from its seeming to be of the same color as the tiles:
in reality it was a bright green. On another occasion I perceived no difference in the complexion of a foreign lady,
who had purposely substituted Prussian blue for her rouge."
Dr. Nicholl says of a boy, eleven years old, -
"I placed a scarlet paper on the grass, and afterwards a
green baize. He said that the grass and the baize were of the
same color as the paper, but that they were a shade lighter.
I made him put on a pair of green spectacles, which he
called red glasses. He said that everybody and every thing
in the room had a reddish cast when seen through them.
The border of the room had a blue leaf with a green edge:
this he called a blue leaf with a red border. A woman
passed by with a basket on her arm. He told his mother that
the woman had fowls in it, for that he saw the red feathers
hanging out: these proved to be green leaves with which she
had covered her butter. He told me, ' What you call purple
and pink and blue are so like each other, that I cannot well
know one from the other.' He also called the gray eyes of




10              COLOR-BLINDNESS:
his sister a bluish red. A blood-relative of this lad was in
the navy, and purchased a blue uniform coat and waistcoat,
with red breeches to match the blue. I showed him a doily which was red, having a leaf of the same color traced
out on it, and I asked him the color of it. He, having been
so often mistaken and laughed at, said, with an air of triumph, ' Why the groundwork is red; but the leaf is of course
green.' "
Dr. Nicholl's second case, a gentleman forty-nine
years old, said, -
"If railings were painted red, I could not distinguish
them from the grass. The grass in full verdure appears to
me what other people call red; and the fruit on trees, when
red, I cannot distinguish from the leaves, unless when I
am near it. A cucumber and a boiled lobster I should call
the same color, making allowance for the variety of shade to
be found in both; and a leek in luxuriance of growth is to
me more like a stick of sealing-wax than any thing I can
compare it with.'"
In further illustration of the sort of mistakes
the color-blind make, I here quote some of Professor Wilson's cases. A middle-aged gentleman
says,
" As far as I can tell, the following expresses my experience as to colors. Yellow is the brightest color; blue, nearly
as bright. These two are the only ones I see distinctly ia
the rainbow. Red I can distinguish when bright; but delicate shades I confound with stone-color or gray. Green I
have no distinct conception of. According to its different
shades, it appears black, brown, red, yellow, blue, and gray.
I cannot distinguish at any distance the ripe, cherries oh~tree, or strawberries from their leaves. I have no conception of what is meant by complementary colors, or of the
agreement of different colors when blended together; as, for
instance, what kind of a carpet accords with red curtains in
a room. With regard to my want of perception of green, it
appears to me that the blue and the yellow rays neutralize
each other, and, when in equal proportions, constitute what is




ITS DANGERS AND ITS DETECTION.


11


really no color, varying all the way from a very light drab
or gray to a dingy black. When the blue rays predominate,
it appears a blue drab; and, when the yellow rays are in excess, it appears a yellow drab. When the blue and yellow
are properly blended, a lady's green silk dress appears to me
very similar, and no more glaring than a drab silk. The
dry dirt of the street I could equally suppose to be green.
I also confound red and brown frequently. I could not distinguish between treacle and blood spilt in a road by daylight."
Another gentleman gives a very interesting illustration of the extent of his color-blindness in reference to red and green. When acting as assistant
to the engineer of the Granton Railway, he frequently returned in the evening from Granton to
Edinburgh on one of the engines, without, however, taking any part in managing, it. On these
occasions he observed, that, although his undivided
attention was directed towards the signal lamps,
the light of which was visible to him a long way
off, he could not, till he was close upon them, distinguish whether they were red or green. He feels
certain that he could tell a blue light from a red
light at a distance which would make green and
red appear the same.
Another gentleman was, like many other colorblind persons, a great lover of fine arts, and a
skilful draughtsman. He was led in consequence,
early in life, to discover his inability to arrange
his own palette, and was accustomed to rely upon
a relative to select his colors, whilst he had no
difficulty in graduating their shades. In the rainbow he distinguishes blue, yellow, and orange.
Green he never sees in it, and he is very uncertain
as to red. In colored objects he has no difficulty




12


COLOR-BLINDNESS:


with blue or yellow; but he stumbles at red and
green, and olive and brown. Green moss and red
and green velvet make the same impression on his
eye, so far as color is concerned. He is foiled also
by worsteds of these colors, and on one occasion
betrayed his peculiarity of vision by his inability
to see the contrast between the scarlet berries and
green leaves of the mountain-ash. On another
occasion he was surprised to find, on returning
home from a journey, that a letter which he had
written home during his absence was one-half in
black and the other in red ink. A red-brick
house, which to others is a conspicuous object in
the landscape, even at a great distance, is to him
an inconspicuous one, and made out with great
difficulty solely by its form.
" Green and red I cannot distinguish from each other.
Red cabbage growing, pickled, or in infusion, are all the
most beautiful blue I can conceive; and it was by not observing any change by acids in the infusion of red cabbage,
when attending Professor Hope's chemistry-class, where I
used to stare for the whole hour expecting to see the change,
that I first became fully convinced of my great defect.
Red, again, in the lips, cheeks, nose (red), gooseberries, inflammations, and the like, looks blue to me! (I never saw
a red nose in my life; ) and yet, in recently taking up an oilpaint, to illustrate to another my conception of the color of
the lips, you will be astonished to hear that I took up a
green (terre verte). On another occasion I was very much
annoyed at a little boy who tould tell a blue line of watercolor, drawn across my finger, from blood: I could see no
difference. Strawberries, cherries, &c., I can recognize without the slightest difficulty; but I don't trouble myself about
their color: I see only a difference as regards what I call
shade. Pinks, lilacs, purples, and blues are all the same,
color, only differing in intensity. Browns, russets, maroons,
olives, citrines, and a host of others, are just any thing I




ITS DANGERS AND ITS DETECTION.


13


can guess at; but I never get farther than red, brown, or
green. The names of the other colors I don't think I ever
uttered. Indeed, I never speak of colors, unless I cannot
avoid it; and the only practical mistake I ever made in regard to them was purchasing a purple neckeloth under the
impression it was black. That was the only mistake, for a
good reason: I never bought a colored piece of dress alone,
either before or since. A piece of railway red signal-glass,
and another of green signal-glass, held up together, close to
the eye in daylight, appeared to be shades of the same
color. "
An engraver reports,
" Strange as it may appear, my defective vision is, to a
certain extent, a useful and valuable quality. Thus: an engraver has two negative colors to deal with; i.e., white and
black. Now, when I look at a picture, I see it only in white
and black, or light and shade; and any want of harmony
in the coloring of -a picture is immediately made manifest
by a corresponding discord in the arrangement of its light
and shade, or, as artists term it, the effect. I find at times
many of my brother-engravers in doubt how to translate
certain colors of pictures, which to me are matters of decided certainty and ease. Thus to me it is valuable. From
childhood I hlave been totally unable to retain certain colors
in my mind, nor able to give their names when shown to
me a second time. This defect applies more particularly to
compound colors, such as green, purple, orange, and brown
(this color I can never define); also the difference between
pink and pale blue, reds and yellows, blues and greens, reds
and greens; but the appreciation of the various shades of
colors (or the weight of colors, as I may term it) is exceedingly nice and critical. A few years ago I went to a draper's to buy some green baize, but unfortunately bought a
very bright red, which was excessively painful to my eyes
by lamplight, but agreeable enough by daylight."
An amateur artist, who also worked with crayons, found his defect an advantage, and reports,"II have myself a distinct perception of the whole spectrum, with the exception of the red and green, which seem




14              COLOR-BLINDNESS:
to be a very near repetition of the same colors; the difference between them being to my eye much more marked by
some accidental variation of tone rather than of tint, which
to others is frequently imperceptible. The flowers of a
fuchsia, the berries of mountain-ash and holly, are scarcely
distinguishable to me, excepting by their tone or form."
He also adds, "I recollect the late Lord V. joking his
wife for wearing a scarlet dress. She assured him it was
bright green; and, comparing notes with him, I found that
our defect of vision was precisely the same, although he
had been scarcely aware of it till that time. My brother,
who has the same trouble, once picked up a red-hot coal,
asking what that funny green thing was."
Another case writes as follows:" I do not think I should easily mistake a green for a
red, or red for a green; but, if the distant perception of
scarlet (or red of that nature) is a necessary qualification
for an engine-driver in the conduct of aC train, I shall be
careful, 'come what come may,' never to offer myself in
that capacity to a railway company. At a distance of about
sixty yards it would puzzle me to distinguish the color of a
soldier's coat, although the general outline of the figure
would enable me to pronounce upon its being that of a
soldier."
An admiral in the British service writes,
" A younger brother of mine, long since dead, was fond
of drawing; yet once he painted a red tree in a landscape
without being aware he had done so. I myself, though fond
of drawing, never attempted to color, as I should have done
the same, unless the cake of color had been properly marked.
I find that it is not that I do not see a distinction between
two colors when placed near each other, as in patterns or
bales of cloth; but I should hardly distinguish a red jacket
hung on a tree, unless quite fresh from the loom. A redtiled barn I should not distinguish in a landscape, but from
knowing tiles are red. The shades of green, of brown, and
of red, perplex me most. Bright scarlet is unmistakable to
me; but I chose a pair of green trousers once, thinking
they were brown. As for signal-lanterns, I should know




ITS DANGERS AND ITS DETECTION.


15


the difference between red and green if they were shown
together; but I should be sorry if the safety of a train
depended on my lookout, when one light alone was exhibited
as danger or no danger."
A young physician answers, "Having often observed a
railway signal-light, seen from my window, I am convinced
that its colors would be lost upon me; nor dare I trust to
their flags. I never venture on the purchase of colored
articles without a companion to appeal to."
Professor N. says, "I suppose I can sometimes distinguish red in some objects, but probably this is from knowing
that they are usually of this color. At any rate, I am quite
sure that I should make a dangerous railway-signal man, as
I most certainly would not know a red flag from a green
one."
An architect reports having to release a pupilapprentice in consequence of finding him copy a
brown house in bluish-green paint, the sky rosecolor, and roses blue.
A tradesman reports his boy offering pink and
pale-green paper as good matches, and getting his
master into frequent trouble by binding books in
wrong colors.
A manufacturer reports that one of his weavers
had to have the red and green threads selected by
another, as he could not distinguish them.
A carver and gilder, who was color-blind, had a
son who painted a head with the face muddy
green, which he conceived to be vermilion. A
brother of this person, an artist by profession,
knew no difference by gaslight between the variously-colored bottles in a druggist's window, and
could not distinguish the red from the green signallamp at a railway-station.
Six males -uncles, nephews, and cousins -in
one family all belong to the Society of Friends;




16


COLOR-BLINDNESS:


and their mistakes in selecting articles of dress
have been rendered especially conspicuous by the
preference which members of that religious body
give to the least brilliant and most unconspicuous
colors. One of their number provided himself
with a bottle-green coat, intending to purchase a
brown one; and selected for his wife, who desired
a dark gown, a scarlet merino. Another, who is
an upholsterer, purchased scarlet for drab, and
had to rely upon his wife and daughters to select
for him the fabrics needed in the course of his profession. A third, who is a farmer, could not tell
red apples from the surrounding green leaves, except by their shape. All of them confounded red
with green, olive with brown, and pink with bluee;
but they are very expert at matching shades of
the same color. One of the younger men, whose
profession requires him to deal much in colored
tissues, has found that the "only way of telling
the difference between scarlet and green, or blue
and crimson, is to take them into a room lighted
with gas or candles," when the distinction which
was invisible by daylight becomes apparent.
Olives and browns, however, are as undistinguishable by one light as by another. A minister, also
in the Society of Friends, selected scarlet cloth as
the material for a new coat.
As to females with color-blindness, Wilson says
of the Countess of D.," Red, green, black, brown, and lilac, she does not venture to name confidently, and greens and drabs are the same
color. Mountain-ash or holly berries are undistinguishable
from their foliage. In sorting worsteds she can place no
confidence in herself in choosing, and all the lightest shades
of color are liable to be completely mixed up. ' The yellow




ITS DANGERS AND ITS DETECTION.


17


tints now (October) seen on the trees appear to me exactly
the same as those of their spring shades: indeed I cannot
conceive the possibility of any one seeing them to be different.' The term 'yellow' here included all the autumn
tints of the leaves; and therefore various shades of orange,
red, russet, and brown must have seemed identical with the
yellow green and the bright green of the spring leaves."
A lady reports, "1 I do not know how to express myself
well regarding the loss I ani at to distinguish colors, as I
hardly understand how it is myself; but I will try to do so as
clearly as I can. There are many colors the shades of which
I confound: these are blue, lilac, pink, and purple; and, if
the various shades of these colors were put before me and
mixed together, I should be quite confused, and could not
tell to which each belongs, although I see they are different.
In the same way I confound green, brown, and some of the
shades of orange. In short, were I to tell the name of any
color correctly, it would be merely guesswork. I can enjoy
the beauties of nature, and the varied hues of the trees, &c.;
but that there is some defect in my vision I am quite aware.
Of this, also, I am certain; I can do nothing (or as yet have
not been able) to improve it."
When engaged with colored worsted-work, she
always has the skeins marked.
To this long list of foreign and American reports, I could, of course, now add as many more
from my own experience with the color-blind. I
will forbear giving but a few, merely to show that
they all can be brought under the same general
laws.
Dr. Blank writes me, " Possibly you may have
recollected that I am myself of the red-green
group. In 1854-55 Wilson of Edinburgh added
me to his list."
Another physician writes me, "I read with interest your color-blind researches: for I am shockingly so, often to my great chagrin and the morti



18


COLOR-BLINDNESS:


fication of my wife and daughter, and, where I feel
it most, in surgical practice, - color of throats,
gangrene, ulcers,' coppery-hued sores, &c.; so that
I have to draw out the statements of others for
my guidance."
A gentleman tells me, " Yellow and blue are my
only distinct colors. Red is the most indistinct.
I cannot see certain shades of red. I cannot distinguish scarlet salvias a few rods away."
A member of a well-known American color-blind
family sends me word, "Red, brown, and green,
of about the same depth or strength of color, appear about alike to me. The red cherry and the
leaf of the tree look substantially alike."
A lady, whose father was color-blind, writes me
of two of her children, boys (three girls being
free of the defect), that "they do not observe
when a flaming bush of Pyrus Japonica is in flower,
unless near enough to discern the form of the
flower. After having his attention directed to it,
one of them said, ' Oh, yes! I see the flowers now;
but they are not so bright as the leaves.' The
leaves in their young state are of a very yellow
green. Neither of the boys is near-sighted. I first
noticed it in my older boy when he was five years
old. We were in a field, and the girls were screaming with delight over such columbines all around
them. The little boy said, 'Where are they? I
don't see any. flowers.' After having one put in
his hand, and observing the form, he, too, could
find them. There are two colors my boys are
quite unable to learn to distinguish. These are
a light green and a yellow brown. I do not think
they see any difference between them. I enclose




ITS DANGERS AND ITS DETECTION.


19


bits of the colors I mean. I omitted to mention
that my boys always call crimson blue."
The green worsted I found almost the same as
the shade used in Holmgren's test, and the yellowish brown just the color the color-blind will select
among the first, if not the very first, to match the
green.
A colleague at a distance, regarded by his wife
as very deficient in color-perception, asked my
opinion. I sent him my test-worsteds; and the
matches he returned me were amusing, fully substantiating the lady's opinion and diagnosis.
A friend told me he painted a pea-green lion for
his little boy. Another wore a green and a brown
glove. A young architect put a green roof on a
church, and was indisposed to admit having made
any mistake. Complaints to me from the colorblind, as to the colors of horse-cars by day and
their lights by night, have been very frequent.
A medical friend tells me that on a yacht he must
have a piece of red glass marked red, and green
marked green, to look at, to endeavor to impress
on his eye the sensation, and compare it with the
red or green light of an approaching vessel. His
matches of worsted were amusing, and showed
complete red-blindness. I happened to meet him
on the street; and, on questioning him, I found he
could see no color in a bright-red express-wagon, a
brilliant new scarlet " soldier's messenger " cap, nor
oould he distinguish a lad by his deep-red scarf.
His brother was nearly the same. Yellow-stained
glass in a door they recognized, but thought pale
green was white, or "1 the color of soda-water."
As has been truly said, "Volumes might be




20


COLOR-BLINDNESS:


written on this subject if the different instances
of all the peculiarities presented by color-blindness,
and all the embarrassment to which they give rise,
were cited."
The question of correctly distinguishing colors
comes up in a practical form more often than we
imagine in every-day life. Such articles as the
following, clipped from the newspapers of a day,
attract naturally the attention only of those
specially interested in or investigating color-perception: -
"NEW BEDFORD, Aug. 30. - Masters of vessels arriving
at Vineyard Haven complain, that, since the red light at the
East Chop has been removed to the new tower built for it,
it is scarcely distinguishable from the West Chop, or any
other fixed white light. The captain of schooner ' Hannibal,' of Islesborough, Me., made it on Saturday evening, approaching from the eastward, in thick weather, and called it
West-Chop light, and changed his course to run in VineyardHaven Harbor, and just escaped running ashore near Oak
Bluffs by making the light at that place through the fog.
Such accidents as the above can only occur, however, in
thick weather, when but one of the two lights on the Chops
of the harbor can be seen at the same time."
"An English inventor, J. J. Nickoll, has brought out a
system of helm-signals. In describing his invention to the
Inventors' Institute, Mr. Nickoll says, ' As my signals move
automatically with the rudder, every material shifting of
the helm to the port or starboard is at once shown at the
head of the vessel by a red or green light, and before she
answers her helm, thus giving timely notice to an approaching ship what course she is about to steer. The signals act
independently of the regulation mast-head lights.' "
As if the present necessary marine-signals were
not difficult enough to read quickly, a writer in
"The Scientific American" proposes that there
should be exhibited a red light for north, green for




ITS DANGERS AND ITS DETECTION.


21


south, yellow for east, and white for west. When
steering due north a red light is to be shown;
when steering north-north-east one light under
this; north-east two lights; east-north-east three
lights, &c.; and so on for the other points of the
compass. Every change of course is to be immediately followed by a change of these lanterns.
Such a proposal but expresses the general lack
of appreciation of the difficulties with all nightsignals.
"The Eastern Railway Company has recently placed
upon the whole route of its line patent switches painted
red, with an index pointing across the track if all is not
right. At night a green lantern signifies the track is clear,
and a red one if not. The company claims that by this
simple arrangement accidents will not be of so frequent
occurrence as under the old system of signals."
jA post-office clerk in Prussia was found to be
constantly in trouble with the stamps. The accounts would come wrong. Sometimes there was
not enough money in return for stamps sold; and
on other occasions there was too much.      This
made dishonesty on his part less likely; but it
was incomprehensible how he would make the
accounts so entangled. At length it was discovered that he was color-blind, and could not
distinguish  red from  green  stamps ("Boston
Medical and Surgical Journal," Dec. 27, 1877).
No doubt letters in the United States find their
way to the Dead-Letter Office as unpaid from the
color-blind senders putting on red two-cent instead
of green three-cent stamps, since we all, from habit,
regard the color rather than the number on a
postage-stamp, especially when in haste.




22


COLOR-BLINDNESS:


CHAPTER III.
FORMER CLASSIFICATION OF THE COLOR-BLIND.
BY this long list of reports from the examiners
or the examined, I have not only enabled my readers to recognize what are the mistakes the colorblind make, but also, perhaps, assisted them in
grouping into certain classes those with this chromatic defect. This, as will be seen, is of importance; but it was not done till 1837 by Professor
Seebeck. Of course any one observer of this
then simply scientific curiosity had hardly opportunity of comparing any great number of cases
together, and thereby deducing some laws concerning them, or sorting out the color-blind into
classes according to their special form of trouble.
Seebeck personally investigated a number for that
time very large, - namely, twelve cases; and he
was the first to work philosophically, recognizing
and insisting on the uselessness of asking the colorblind the color-names of objects. He proved the
importance of letting them show their own comparisons by having a number of colored objects
mixed up together, and allowing them to select
and group together those which seemed to them




ITS DANGERS AND ITS DETECTION.


23


of the same color. He had some three hundred
pieces of variously colored paper, also variously
colored pieces of glass. Ile recommends worsteds,
but thinks silks would be too brilliant. He did not
use worsteds, but did employ the spectrum and
polarized light in addition to the test with the
colored papers, &c.
His deductions were, that there was a class of
color-blind who seemed quite insensible to the specific impression of all colors, - most so for red and
naturally, also, its complementary green, in that
they could distinguish them but little, if any, from
gray; then for blue, which they did not well separate from gray. Their sensation of yellow seemed
best developed, though this did not appear so different from colorless as to a normal eye. Such persons more or less confounded bright orange and
pure yellow; deep orange, bright yellowish or
brownish green, and yellowish brown; pure bright
green, grayish brown, and flesh-color; rose-red,
green (rather bluish than yellowish), and gray;
carmine, dark green, and hair-brown; bluish green
and impure violet; lilac and bluish gray; skyblue, grayish blue, and grayish lilac.
Another class he found very similar to the first.
They also recognize yellow best, and distinguish
red better, blue rather less from colorless, but
especially confound red and blue. The colors
they confound with each other are clear orange,
greenish yellow, brownish yellow, and pure yellow; bright orange, yellowish brown, and grassgreen; sealing-wax red, rusty brown, and dark olive
green; cinnabar-red and dark brown; dark carmine red and dark bluish green; flesh-red, gray




24


COLOR-BLINDNESS:


b)rown. and blue green; pale bluish green and
gray (rather brownish); impure rose (rather yellowish) and pure gray; rose-red, lilac, sky-blue,
and gray- (towards lilac); carmine and violet;
dark violet and dark blue.
Seebeck was the first, besides grouping the colorblind into classes, to show also that there were
degrees of this trouble as varying as the visual
power for form, which we now recognize as individual.
Again, from an analysis of our long list of reported difficulties with chromatic vision, we may
see how it was, from a study of all the then accessible cases, Szokalski distinguished Jive classes
of color-blind, -
1. That of persons in whom the sense of colors is
almost completely wanting, and who, in place of
the elementary colors, -yellow, red, and blue,see only different degrees of white and black.
2. That of persons who also distinguish yellows: external objects appear to them colored
with shades which generate the different mixtures
of yellow, of white, and of black.
3. That of persons who, besides seeing yellow,
have a common perception for both blue and red.
4. That of persons destitute solely of the perception of red, which appears to them ash-gray.
5. That of individuals who distinguish all colors, but not in a decided manner: instead of being
able to distinguish the mixture of two colors, they
never see but one of them.
Professor Purkinje, again, from an analysis of
cases observed and then recorded, divides colorblindness into four varieties. The first two re



ITS DANGERS AND ITS DETECTION.


25


late more to the intensity, the others to the nature, of the imperfection.
Professor Elie Wartman, writing in 1840, says, -
"The various ancient and recent observations which I
have to relate appear to me to confirm the division of Seebeck, rather than that of Szokalski and Purkinje. It would
be very advantageous to make a strict classification of the
color-blind, because for each category means might be offered at once simple and few as palliatives of their imperfections. Unhappily such an undertaking does not seem
possible, and we may say that there are as many varieties of
color-blindness as of individuals who are affected with it.
With regard to the very rational distinction which Seebeck
has the merit of having first established between the errors
of appreciation of intensity, and those of judgment of the individual kind of colors, it is to be regretted that we cannot
make it in the great majority of the descriptions which writers have transmitted to us. I prefer only to separate the
cases of dichromatic and polychromatic color-blindness; that
is to say, where there are more than two colors perceived
normally."
I have thus briefly given the earlier attempts to
classify the color-blind, that the difficulty of so
doing may be recognized. We shall also thus be
better able to appreciate the value of the application of the theory for this purpose described in
the next chapter.




26


COLOR-BLINDNESS:


CHAPTER IV.
PRESENT CLASSIFICATION OF THE COLOR-BLIND
IN ACCORDANCE WITH THE YOUNG-HELMHOLTZ
THEORY OF COLOR-PERCEPTION.
A PROPER division, and a consequent correct
understanding, of color-blindness was not made
till this half of our century.    Professor Helmholtz brought forward the long-forgotten work of
Thomas Young, and applied his theory of colorperception to the results of more modern investigations, with the final development of what is now
called the Young-Helmholtz theory of color-sense.
Helmholtz says, -
"A reduction of colors to three base colors has only a
subjective meaning: it is but reducing or carrying back the
sensations of color to three base or final sensations. In this
view Thomas Young correctly grasped the problem, and, in
fact, his theory gives us a very simple and clear view and
explanation of all the phenomena of the physiology of color.
Thomas Young holds that, -
"1. There are in the eye three kinds of nerve-fibres.
Stimulation of the first produces the sensation of red, the
second that of green, and of the third the sensation of violet.
"2. Objective homogeneous light excites these three
kinds of fibres in varying degree according to the wavelengths. The red perceptive fibres will be strongest stimu



ITS DANGERS AND ITS DETECTION.


27


lated by light of the greatest wave-length, the green perceptive by light of medium wave-length, and the violet
perceptive by light of the smallest wave-length. Here must
not be excluded, but rather accepted in explanation of a
series of phenomena, that each spectral color excites all
three kinds of fibres, - but one less, the others more strongly. Let us suppose, as in Fig. 1, the spectral colors in a
horizontal row from red to violet: then the three curves will
represent the intensity of stimulation of the three kinds of
fibres, - (1) the red perceptive; (2) the green perceptive;
and (3) the violet perceptive elements or fibres.
1               2                3
R.       0. Y           G          B          V
Fia. 1.
"Simple red strongly stimulates the red perceptive, less
the other two: sensation, red.
" Simple yellow stimulates moderately the red and green
perceptive, feebly the violet: sensation, yellow.
" Simple green stimulates strongly the green perceptive,
much less the other two: sensation, green.
" Simple blue stimulates moderately the green and violet
perceptive fibres, feebly the red: sensation, blue.
" Simple violet stimulates strongly the violet perceptive,
feebly the other fibres: sensation, violet.
"Equally strong stimulation of all the fibres gives the
sensation of white or whitish colors."
This is not the place to discuss the YoungHelmholtz theory of color-perception. It must be
remembered that the facts in relation to colorblindness given in this volume are not collected
in support of any theory, nor is any theory argued
for. The Young-Helmholtz is used rather as a
means of better explaining this defect. It will




28


COLOR-BLINDNESS:


assist our understanding its relations to colorblindness to read Helmholtz's explanatory introduction of it: -
"Perhaps there will be much objection to this hypothesis, from the number of the necessary nerve-fibres or nerveterminations being tripled, in comparison with the common
theory, where every individual nerve carries all possible
color-stimulations. I do not think, however, that in this
respect Young's theory is in opposition to anatomical facts,
since we know nothing of the number of the transmitting
fibres; and then, besides, there are a number of microscopic
elements present, whose special function we do not as yet
know. Moreover, this is not the most essential in Young's
hypothesis. That seems to me to be rather the presenting
color-sensations as composed of three wholly independent
actions in the nerve-substance. It is not absolutely necessary to suppose separate nerve-fibres for these separate sensations. The same value of Young's hypothesis in this explanation is shown, if we suppose that in each individual
fibre three different and independent actions may take place.
Since, however, the form of the hypothesis, as originally
proposed by Young, is capable of more definite presentation and expression than such a modification of it would
allow, we will, in view of its description, retain the original
plainer form. Moreover, the physical phenomena of nervestimulation - namely, the electro-motor - are not marked in
the sensitive or motor nerves by such a variation in action
as would necessarily be the case if each nerve-fibre transmitted all color-sensations. By Young's hypothesis we may
also apply to the optic nerve the simple conceptions of the
mechanism of stimulation and conduction which we have derived from the study of the phenomena in the motor nerves.
This we could not do if we must admit that each optic
nerve-fibre is to have three qualitatively different conditions
of stimulation without mutual interference. Young's hypothesis is only a more special carrying-out of the law of the
specific energies of the senses. As the sense of touch, and
the sense of sight in the eye, have evidently separate
nerve-fibres, so is the same claimed for the sensation of the
several base colors. The choice of the three colors is some



ITS DANGERS AND ITS DETECTION.


29


what arbitrary. Any three colors could have been taken
whose combination produced white light. So far as I see
at present, there is no other means of determining the base
colors than the examination of the color-blind."
For further description of the Young-Helmholtz
theory of color-perception I would refer the
reader to Helmholtz's popular scientific lectures.
I have given above the essential points, as this
was necessary to enable us to readily follow out
the application of the theory thus stated by Helmholtz to the condition of the color-blind. By
Young's theory Helmholtz has shown how colors
must appear to the color-blind. This has been,
however, so well extended and explained in Professor Holmgren's book, that I cannot do better
than quote from it here. In deference to the
Smithsonian Institute I will give their translation
rather than my own.      Professor Holmgren goes
on to say, -
"These curves (Fig. 1) enable us to explain easily the
colors of the spectrum by the theory. We find in what proportion each one of the three fundamental perceptions enters into it by measuring the vertical distance from their
place on the horizontal line (abscissa) to the corresponding
points of each of the three curves. It is then seen that
there is no color of the spectrum into which but one primitive color enters exclusively. The two others also furnish
their contingent. No one is therefore perfectly " saturated."
They are more or less spread with white, and green is the
least sensibly "saturated," or more whitish. The curves
also show us that yellow and blue are at the same time
whitish colors, and the most intensely luminous in the whole
spectrum. When we again add that a color, " saturated " in
almost the same degree as the other spectral colors, proceeds from the homogeneous combination of red and violet,
— that is to say, purple, and its whitish shade, pink, -we
shall have said all theoretically that we have to say in
relation to the normal chromatic sense.




30               COLOR-BLINDNESS:
" To explain the abnormal sense of colors by the theory
of the normal, we can, in advance, conceive various possibilities. Let us suppose that one of the three fundamental
perceptions is wanting, or that one of the primitive colors is
absent: it is clear that the whole chromatic system will be
upset. It is evident, therefore, that this system must be
completely different, according to the absence of one or the
other of.the three primitive colors. It is virtually just in
this way that it has been attempted to explain cases of a
strongly marked defect in the chromatic sense, or genuine
types of blindness to color, found in real life. The term
color-blindness has been justified by this, as it indicates in
each case a genuine blindness to one of the primary colors.
In this way, therefore, we distinguish, according to the kind
of element wanting, three classes of blindness,1st, Red-blindness.
"2d, Green-blindness.
"3d, Violet-blindness.
" We shall see that the Young-Helmholtz theory, far from
being contradicted, as has been recently claimed, by the
phenomenon of color-blindness, finds in it, on the contrary,
a support; and this theory most certainly furnishes the best
guide for attaining the practical end in view for which we
intend to use it. Let us, in the first instance, cast a rapid
glance over the different kinds of typical and complete
blindness to colors as their features are presented by the
theory. This sketch will be singularly facilitated by the use
of the same kind of curves employed in illustrating the
normal sense of colors.
"1. According to the theory, blindness to red is due to the
absence or paralysis of the organs perceiving red (Fig. 2).
Red-bindness has, then, but two fundamental colors, which,
adhering strictly to the theory, are green and viblet (blue
according to Maxwell).
"The curves distinctly show what aspect the various
kinds of lights of the spectrum must have for the chromatic
sense, such as the one we have in view. We will give a
short list of them, according to Helmholtz, by designating
here the different kinds of lights, - by using terms borrowed
from the impressions they produced on the normal chromatic
sense. The comparison will not be without interest:



ITS DANGERS AND ITS DETECTION.


31


"' I Spectral red, which feebly excites the perceptive organs
of green, and scarcely at all those of violet, must conse- /
quently appear to the red-blind a " saturated " green of a feeble intensity, more " saturated " than normal green, into which
a sensible portion of the other primitive colors enters.
Feebly luminous red, which affects the perceptive organs of
red in a normal eye sufficiently, does not, on the other hand,
sufficiently excite the perceptive organs of green in the redblind; and it therefore seems to them black. Spectral yellow seems to them a green " saturated " and intensely luminous;
and, as it constitutes the precisely saturated and very intense
shade of that color, it can be understood how the red-blind
select the name of that color, and call all those tints that
are, properly speaking, green, yellow. Green shows, as compared with the preceding colors, a more sensible addition of
2                   3
0 o             Y      G           B          V
FIG. 2.
the other primitive colors: it then appears, consequently,
like a more intense but whitish shade of the same color as
yellow and red. The greatest intensity of light in the spectrum, according to Seebeck's observations, does not appear
to the red-blind to be in the yellow region, as it does to the
normal eye, but rather in that of the blue green. In reality,
if the excitation of the perceptive organs of green, as it was
necessary to assume, is strongest for green, the maximum of
the total excitation of the red-blind must be found slightly
toward the blue side, because the excitation of the organ
perceiving violet is then increased. The white of the redblind is naturally a combination of their two primitive colors
in a determinate proportion, -a combination which appears
blue gray to the normal sight: this is why he regards as
gray the spectral transition colors from green to blue.
Then the other color of the spectrum, which they call blue,
preponderates, because indigo-blue, though somewhat whit



32               COLOR-BLINDNESS:
ish according to their chromatic sense, is to them, owing to
its intensity, a more evident representative of that color than
violet.'
" This description of the manner in which the red-blind
forms a conception of the different kinds of light of the
spectrum is assuredly a conclusion logically deduced from
the theory; but it accords so well, at the same time, with the
experience acquired in examining the color-blind, that this
might perfectly serve to support and corroborate the theory.
We will simply add a point for our especially practical purpose, or rather emphasize one point of this theory. In fact,
it is clear that a red and a green light especially excite one
and the same element in the red-blind. A ray red and
green, or an object red and green, to the normal sense, must
seem fundamentally to the red-blind to be the same color;
and if, in especial cases, he knows how to discriminate, his
judgment is simply guided by the intensity of the light.
The intensity of light is much more feeble (as shown by
Fig. 2) in red than in green. If, then, a red-blind individual
finds that a red and a green tint are exactly alike, it is necessary that the green be to the normal eye much less intense
than the red. This is distinctly shown by the vertical dotted lines between R. and 0., and also between Y. and G.,
in Fig. 2; and this is entirely confirmed by experience.
"2. Green-blindness derives its origin, according to the
theory, from the absence or paralysis of the perceptive elements of green. The green-blind has therefore but two
fundamental colors; that is, - still closely adhering to the
theory, - red and violet (blue according to Maxwell). The
spectrum for green-blindness should be, according to the
theory, constructed in the following manner: -
" The spectral red, which strongly excites the perceptive
organs of red, and but very faintly those of violet, must
therefore appear to the green-blind as an extremely' saturated' red, but of a light somewhat less intense than the
normal red, which is comparatively more yellowish, as green
forms a part of it. The spectral orange is again a very
'saturated' red, but much more luminous. Yellow is undoubtedly a more intensely luminous red than the spectral
red, but, on the other hand, more whitish, because a sensible
portion of the other primitive color enters into it.




ITS DANGERS AND ITS DETECTION.             33
"Green, with its shades inclining to yellow and blue,
ought, correctly speaking, to be a 'saturated' purple, and
with a mean intensity of light: but it is the white (gray) of
the green-blind; for it is composed of almost equal parts
of the two primitive colors.
" The blue is an intense violet, but a little less ' saturated'
than indigo, which is more strongly luminous and more
' saturated.' Violet is a little less intense, but more ' saturated' than normal violet. The tints most luminous, and at
the same time most ' saturated,' which must constitute the
types of the primitive colors of the green-blind, are orange
(or its immediate neighbor in the spectrum, red) and indigoblue. Now, orange is a color which, in ordinary language,
especially amongst the uncultivated and unpractised, is indiscriminately called red and yellow: this fact explains why
the green-blind denominate their first primary color some1                                3
R       0     Y        G           B        V
FIG. 3.
times 'red' and sometimes ' yellow.' We will add to this
description the same remark made about red-blindness. In
green-blindness the same organ is also found affected by
spectral red and green light. Red and green are then perceived by the green-blind in the same way, or, in other
words, are to him in fact exactly the same color. In cases
where he succeeds in distinguishing them, it is by the aid of
the intensity of the light; but, with regard to this intensity
of light, it is the opposite of what occurs in the case of the
red-blind. A green tint which to the green-blind must appear exactly like a red one, to a normal sense of color must
be sensibly more luminous than red. This is shown by the
dotted vertical lines between R. and 0., and also between
Y. and G. (Fig. 3), and is confirmed in every respect by
experience.
" Violet-blindness (or blue according to Maxwell) is due,




34


COLOR-BLINDNESS:


according to the theory, to the absence or paralysis of the
elements perceiving violet. The two primitive colors of the
violet-blind are then, according to theory, red and green.
The spectrum of the violet-blind must, in consequence, be
represented as follows:" The red is a purer red color (not yellowish) than normal
red, but still less ' saturated.' The more it inclines toward
orange, the more strongly luminous it is, but is at the same
time less 'saturated,' more whitish. The yellow is, as it
were, a combination of almost equal proportions of the
fundamental colors that form white. Green is a strongly
luminous but whitish green, which, in tending toward the
blue, becomes more and more ' saturated; ' so that greenish
blue must be the type of these hues. The blue is a green of
moderate luminosity, and strongly ' saturated;' and violet is
green very feebly luminous, but also ' saturated' in a much
11      o      Y       G         B        V
FIG. 4.
higher degree than the normal. A violet strongly luminous
is sufficient to induce this green; but a feeble violet, although
very sensible to the normal eye, is black to the color-blind
in question.
" It is plain that the violet-blind, whose primitive colors
are red and green, do not confuse these colors. This kind
of blindness, from the experiments made so far, must be
very rare. For our part we have not succeeded in discovering more than two cases agreeing quite exactly with the
description given by the theory; while the first two kinds
are comparatively very common. In order to be abnormal
it is not necessary that a sense of color should completely
fulfil the conditions indicated in the types we have just
described. We might perfectly conceive a resultant, not of
an absolute absence or of a complete paralysis of one kind
of perceptive elements, but solely of a comparatively very




ITS DANGERS AND ITS DETECTION.                     35
low excitability, or, if preferred, of a much more limited
number of one kind of elements, acting on the retina, as
compared with the two other kinds. It is very easy to construct curves in conformity with this idea, and not less easy
to arrange in this manner a continuous series of transitions
and gradual forms between one kind of complete color-blindness on one side and the normal chromatic sense on the
other. This kind of defective vision might be called incomplete color-blindness, to distinguish it from  complete, as we
have just characterized the three different kinds. Our experience has taught us that the intermediary forms agreeing
with the data given above are met in large numbers in practice, and of very different degrees. These are the forms we
designated under the common appellation of incomplete colorblindness; but we can, according to the theory, still conceive
other forms of a defective sense of color. There is one,
amongst others, which has at command only one of the
three kinds of elements.    Such a sense of sight is not properly a chromatic sense. For it there exists no specific difference in light; that is to say, no color. Every kind of light
here acts as if on one element alone. This is why the
single perception of differences of intensity of light (quantity), but not of differences of color (quality), is possible.
This condition may then be designated under the name of
total color-blindness.  Several cases have been mentioned
from time to time; but we have not succeeded in finding a
single one, and it may well be questioned whether such a
case has actually existed.1 We may also conceive that
1 Professor Donders reported an interesting case of congenital total colorblindness at the Heidelberg Ophthalmological Society 1871: An educated
young man of twenty-one years of age was totally color-blind. Strong light
blinded him: in moderate light he saw very well. He was myopic one-eighth,
and read for hours without glasses. Out of doors, all glasses which absorbed
light, without difference, -even the brightest colored ones, -were pleasant to
him, because they reduced the light. In the dioptric spectrum of a gas-lamp
his brightest part was between the spectral lines D and E, close to E: hence
in greenish yellow. From here outwards towards the red end the light faded
rapidly; towards the violet, at first, slowly, then rapidly. By moderate illumination he lost less of the brightest of the spectrum on this side than
towards the red end. With the polariscope, the complementary colors
through the quartz plate appeared to him of the same color. In turning the
double-refractive prism he had a maximum of hrigltness at every ninety
degrees, or equality of brightness, as if the quartz plate was not there. He
had the greatest difference when Donders himself saw purple and green;
equality, when he saw yellow and blue. Trials were also made with Che.
vrcul's chromatic circle.




36               COLOR-BLINDNESS:
another form of a defective sense of color arises from the
three kinds of elements being uniformly of moderate sensibility. We are able to trace the following diagram (Fig. 5),
by which the three curves simultaneously approach the abscissa, or horizontal line, and are flattened in such a manner
that the vertices disappear the first.
" As is readily observed, green is then precisely the color,
which, being ordinarily the most whitish of the primitive
colors, is the first to lose its quality of ' saturated' color,
and shades into gray. This must then be the exact scheme
of pathological color-blindness, according to the theory. In
fact, we have found in our examinations a large number
of cases perfectly harmonizing with this scheme. We have
therefore classed them under the head of incomplete colorblindness; and this from essentially practical reasons. To
define their nature according to the theory, it is necessary
R        0     Y       C           B         V
FIG. 5
to regard them as a particular variety, which we shall call
a feeble sense of colors. We are not of course able to decide
how far defects of this kind should be considered as having
a pathological origin, or whether they are ever congenital.
For this determination a much wider experience in this particular department than we now possess is requisite, for reasons to be given hereafter.  This kind of defect in the
sense of color leads - if we fancy it carried to its highest
degree, or in such a condition that all the elements lose sensibility -to the complete absence of perception of light;
that is to say, to blindness, strictly so called. Every defect
in the sense of color must then proceed either from a sensibility anomalously reduced to a complete paralysis of one
or several kinds of elements, or from a number relatively
diminished in sensibility to the complete absence of one or
several amongst them.
" The experience acquired by an examination of colors in




ITS DANGERS AND ITS DETECTION.             37
different parts of the visual field elucidates our theory of
color-blindness, while at the same time having a practical
value. The following is the manner in which this examination is conducted: The eye is fixed upon an immovable
point; a colored object -for example, a colored paper one
or two centimetres square - is slowly passed from the side
of the visual field toward the fixed point. This experiment
is performed still better by means of a special instrument,
Forster's perimeter. We then find that the colored surface
of any color whatsoever appears completely colorless at the
extreme periphery of the visual field. Surfaces of different
colors exhibit only variations in intensity of light, not in
color. The ground on which the surface appears plays here
an important part, since, every time our visual sense perceives the light and color of an object, it partly depends
upon the comparison with that which surrounds it. Thus
a colored surface seems to us, in this part of the visual field,
black or gray on a light ground, and gray or white on a
dark. If, while following the same direction, the colored
object is carried within the region which surrounds the rest
of the visual field, like a belt of greater or less width, we
begin to see the colored object, but not always in its natural
color. Two colors alone - yellow and blue - retain their
natural colors. All the others have the appearance of one of
these colors consequently, - yellow or blue. It is only after
the colored object is carried a little farther toward the fixed
object that it is seen in its natural color. Consequently we
normally see colors only in the middle of our visual field,
within a compass extending in a more or less eccentric manner in every direction from the fixed point. Outside of the
central field extends a belt which surrounds it on all sides,
and in which our whole system of colors is classed under
two heads, -exactly as in the case of the red-blind. We
have here, as in the last case, but two colors,- yellow and
blue. In other words, we are completely red-blind in this
intermediary zone: beyond this there is a peripheral belt,
in which we are totally color-blind. These are matters unquestionably of great theoretic value; but it must be acknowledged they are also of great practical importance. Although
we have adopted the Young-Helmholtz theory, we must
admit that the different kinds of perceptive elements of col



38               COLOR-BLINDNESS:
ors have a different local division upon the retina; and this
is why we may speak of the topography of the chromatic
sense. The fact is explained in this way: in the retina of
the normal eye there are simultaneously three kinds of elements in the central part, corresponding to the central
region of the visual field. Toward the periphery, beginning
at the central fossa, the elements become more and more
rare, but in unequal proportions; so that the perceptive
organs of red cease first, and this at a limit corresponding to
that of the central region. In a belt which answers to the
intermediate zone, or the belt of the red-blind, there remains in consequence but the perceptive elements of green
and violet. At the limit near the periphery of the retina, corresponding to that of the peripheral zone of the visual field,
or region of absolute color-blindness, the perceptive elements of green cease also; so that there only remains in this
last zone the perceptive elements of violet. We have been
especially led to this last conclusion by the examination of
two cases of color-blindness, where the visual field was so
abnormally small that the peripheral zone seemed to be
effaced, and where we, besides, recognized the characteristic
features of violet-blindness. This experiment, which perfectly harmonized with the theory, showed us the relation
of complete red-blindness to the normal chromatic sense.
Red-blindness is distinguished from the normal sight in this,
that the normal central field is wanting, but is replaced by a
mean corresponding at the same time to the central field and
to the intermediary zone of the normal sight. We have also
succeeded, owing to the peripheral investigation of the colored visual field, in verifying in a great number of cases
the continuous series of forms of transition, which we have
classified as one kind under the head of incomplete colorblindness, or, in the instance especially occupying us here,
incomplete red-blindness. In the same way the other kinds
of color-blindness may also, as regards the visual field, be
classified according to the theory. The visual field of the
green-blind is distinguished from that of the normal observer
in this, that it has a peripheral field corresponding in extension both to the intermediary and peripheral zones of the
normal observer. The visual field of the violet-blind is distinguished on the other hand in this, that it is completely




ITS DANGERS AND ITS DETECTION.


39


deficient in the normal peripheral zone. These two kinds
of incomplete color-blindness are characterized by a central
field diminished at every degree. With regard to the visual
field, we may therefore lay down this rule, that it has as
many distinct zones, with reference to the perception of
colors, as the chromatic sense has fundamental colors or
different kinds of perceptive elements, and that the different degrees of incomplete color-blindness are in the inverse
ratio to the dimension of the visual field. If the central
field is limited to a circle of ten degrees from the fixed
point, all the respective characteristics of color-blindness
are usually found in it, sometimes within even a narrower
range. A feeble sense of color manifests itself in a much
wider central field. All the anomalies that can be discovered
in an examination of the visual field might, in consequence
of the method employed, be explained by a diminution of
excitability as well as of the number of the elements. The
intermediary zone of the normal visual field or belt of redblindness has an especial interest, as it furnishes us with
the opportunity of seeing with our own eyes as the redblind sees, and consequently of exactly comprehending his
abnormal perception.
"According to the theory, we see only yellow and blue in
this belt, and in consequence we admit that the red-blind
not only call yellow and blue their principal colors, but
moreover see them exactly as the normal observer does.
This hypothesis cannot assuredly be proved; but this is not
necessary, as the explanation Helmholtz has given of the
designation of one of the principal colors of the red-blind is
perfectly satisfactory.  This circumstance, however, has
given rise, amongst others, to a doubt about the YoungHelmholtz theory, and to another theory admitting four
principal colors to the normal sense of colors, yellow being
classed amongst them. But this is useless. It must not
be forgotten that colorless light and colored light are subjective perceptions, and that comparison here performs an
important part. This fact is sufficiently proved by the phenomena of contrasts, accidental colors, &c. White is not a
color: it is merely a general, neutral light, and is therefore
produced when one kind of element is not more excited than
another, or when all the elements are equally excited.




40


COLOR-BLINDNESS:


"But, as the theory obliges us to admit that the excitation of the perceptive elements of green and violet may, in
certain cases, as in the instance of the red-blind, supply the
perception of white, and not bluish green; and that, in certain cases, as in that of the green-blind, the excitation of
the perceptive elements of red and violet does not give purple, but white, - it is in no wise contrary to the theory to
admit that the excitation of the organ perceiving green
gives the perception of yellow in cases where all that remains, moreover, of the system of colors is the complementary color of yellow; that is to say, blue. The excitation of the perceptive organ of green gives the perception of
green only on the retina, or on a point of the retina which
also contains the organ perceiving red. But this is not the
place for further developments of this theory.
"2. -CLASSIFICATION OF THE DIFFERENT KINDS OF
COLOR-BLINDNESS.
"In the preceding we have indicated, in conformity with
the theory, the different forms of a defective sense of colors,
to which, we think, should be applied the name of colorblindness, and which, owing to their nature, theoretically
must be considered as of different kinds. This division
will be sanctioned, if we consider the relations in which it
stands to the method pursued for discovering them, and
which is based on the Young-Helmholtz theory. It is this
we are about to explain.
"We classify the different kinds of color-blindness under
especial heads, to be able the better to grasp the whole.
We might, indeed, divide this blindness into congenital and
acquired; but as such a division has reference alone to the
mode of origin, and not to the nature of this blindness, and
affects in no wise the manner of its discovery, it has no
practical importance in the case now occupying our attention. Besides, our division relates, as does our entire
memoir on this subject, essentially to congenital colorblindness. The division is as follows: -
"I. Total color-blindness, in which the faculty of perceiving colors is absolutely wanting, and where the visual sense
consequently can only perceive the difference between dark



ITS DANGERS AND ITS DETECTION.                11
ness and light, as well as the different degrees of intensity
of light.
" II. Partial color-blindness, in which the faculty of certain perceptions of color, but not of all, is wanting. It is
sub-divided into, -
" 1. Complete color-blindness, in which one of the three
fundamental sensations, one of the three perceptive organs
of color in the retina, is wanting, and in which, consequently, the colored visual field has but two ranges. This
group includes three kinds; namely,s" (a) Red-blindness.
".(b) Green-blindness.
"(c) Violet-blindness.
"2. Incomplete color-blindness, where one of the three
kinds of elements, or perhaps all, are inferior in excitability
or in numbers to those of the normal chromatic sense. Incomplete color-blindness exhibits, like the normal sense,
three zones in the& visual field, but is distinguished from it
by an unusually small central field. This group includes
the whole of a series of different forms and degrees, a part
of which -the superior degrees, which might be called
incomplete red-blindness and incomplete green-blindness (and
incomplete violet-blindness) - constitutes the transitions to
the corresponding kinds of complete color-blindness; and
another part of which - the inferior degrees, which we call
a feeble chromatic sense-constitutes the transition to the
normal sense of colors.
"We will show farther on, that this classification, based
entirely upon the Young-Helmholtz theory, is quite practical, and conformable to experience. We know no classification, which, though distinguishing accurately between the
different essential forms of a defective sense of colors, draws
a surer, more decided, and more practical limit between the
defective sense of colors and the normal sense.




42


COLOR-BLINDNESS:


CHAPTER V.
PRECISE CONDITION OF THE VISION OF THE
COLOR-BLIND.
IT will be now asked, What do the color-blind
see? Does red look green to them, or green red,
or yellow blue, &c.? The fact so long ago noticed
that they could not distinguish their faulty color
from gray, - a mixture of black and white,
and the more color-blind they were the darker the
gray which would match their faulty color, ought,
perhaps, to have had more attention paid to it.
Through this we can, perhaps, get a better idea
of the color-blind's vision. And we may formulate their vision thus: All colors containing their
defective one will be grayish, and this in proportion
to their individual amount of defect.
But let us have the testimony of the colorblind themselves. Mr. Pole, a red-blind, has
tested himself, and shown why his results should
be accepted. He thoroughly understands his own
condition, although he does not seem to quite appreciate the existence of varying degrees of colorblindness, so perfectly shown, for instance, by
Donders in his examination of the railroad em



ITS DANGERS AND ITS DETECTION.


43


ployds in Holland: moreover, violet-yellow-blindness has no place for him, which is, perhaps,
natural.
In a criticism of Mr. Gladstone's Homeric
vision, recently  given   in  "Nature," Mr. Pole
briefly sketches his former extended report of
his case, and Sir John Herschel's notice of the
same. As to how he sees, which interests us, he
says, -
" In the first place, we (the color-blind) see white and
black, and their intermediate or compound gray (provided
they are free from alloy with other colors), precisely as
others do.
"Secondly, there are two colors properly so called,
namely, yellow and blue, -which also, if unalloyed, we see,
as far as can be ascertained, in the normal manner. But
these two are the only colors of which we have any sensation; and hence the defect has been given by Sir John
Herschel the scientific name of dickromic vision.
"But now comes the difficulty of the explanation. It
may naturally be asked, Do we see objects of other colors,
iuch as roses, grass, violets, oranges, and so on? And, if we
do see them, what do they look like? The answer is, that
we do see all such things, but that they do not give us the
color-sensations correctly belonging to them: their colors
appear to us varieties of the other color-sensations which
we are able to receive. This will be best explained by
examples.  Take first the color red.  A soldier's coat
(British), or a stick of red sealing-wax, conveys to me a
very positive sensation of color, by which I am perfectly
able to identify, in a great number of instances, bodies of
this hue. If, therefore, the investigation of my experience
ended here, there would be no reason to consider me blind
to red, or as having any grave defect in my vision regarding
it. But, when I examine more closely what I really do see,
I am obliged to come to the conclusion that the sensation I
perceive is not one that I can identify separately, but is
simply a modification of one of my other sensations; namely,
yellow. It is, in fact, a yellow, shaded with black or gray,




44


COLOR-BLINDNESS:


-a darkened yellow, or what I may call yellow brown. I
find that all the most common hues of red correspond with
this description; and, in proportion as they are more scarlet
or more tending towards orange, the yellow I see is more
vivid. The explanation, I suppose, is, that none of such
reds are pure, - they are combinations of red with yellow;
so that I see the yellow element of the combination, while
the true red element of the combination is invisible to me
as a color, and acts only as a darkening shade.
" I obtain a further proof of this by the change of sensation when the hue of red is altered. I find, that, as the color
approaches crimson, the yellow element becomes fainter,
and the darkening shade more powerful, until very soon the
yellow disappears, and nothing but a gray or colorless hue
is presented to my eye, although the color is still a positive
and powerful red to the normal-eyed; so that there is a
hue of red, which, as a color, is absolutely invisible to the
color-blind.
"If I go on beyond this point, and take reds that pass
from crimson towards the hue called lake, I see my other
color come in, - a faint blue, - which increases till violet is
reached, when it becomes more decided. Violet is understood, I believe, to be a compound of blue with red; and,
accordingly, the red element being invisible to the colorblind, violet hues generally appear to them only as darkened
blue. There are, however, examples where, from the red
being very strong, the blue appears to lose its effect; and
the impression given is colorless, black, or gray. They
correspond, in fact, with the neutral red before described,
although still called violet or purple by the normal-eyed.
This latter effect is much enhanced under the artificial light
of gas or candles.
"A similar observation will apply to orange, - a combination of red and yellow,-in which the yellow only is
perceived.
" The appearance of green to the color-blind corresponds
exactly to that of red. Green, in its true aspect, is invisible
to them; and, consequently, when neutral,- i.e., unmixed
with any other color, -it presents to their eyes the appearance
of gray. When, however, it is mixed with yellow (and most
of the greens in nature are yellow greens), they see the




ITS DANGERS AND ITS DETECTION.


45


yellow only, but diluted or darkened by the invisible green
element; and in less frequent cases, where the green is
mixed with blue, they see the blue element only in like
manner.
"It is therefore easily understood how so simple a defect
of vision gives rise to so complex a series of symptoms as
those already described. Take first the color red. If it is
a scarlet variety, as the majority of reds are, presenting the
appearance of yellow to the color-blind, they may naturally
confound it with the latter color, as well as with orange,
with yellow green, and with brown, - all which cause to
them, the same sensation. If, on the other hand, the red
contains a predominance of blue, it may be confounded,
on the same principle, with blue or violet.  If it is a
neutral red, lying between the two, it will be confounded
with black or gray. A pale pink, though very distinctly
colored to the normal-eyed, often offers so little color to the
color-blind as to be mistaken for white or very light gray.
The same explanation will apply to green.  Its yellow
varieties may be compounded with red, orange, yellow,
and brown; its blue varieties with blue and violet; and its
neutral hue with black or gray, or, if pale, with white."
These statements of Mr. Pole are so valuable,
and so in accordance with the application of the
Young-Helmholtz theory of color-perception to
color-blindness as we now are enabled to analyze
it, that I can not refrain from quoting Sir. John
Herschel's remarks in reference to them. We see
now how the color-blind perceive the colors they
are blind to; and therefore it is important to feel
assured that the red-blind-as, for instance, Mr.
Pole's -perception of yellow and blue is the same
as our own or the normal-eyed. Sir John says, -
"I consider this paper as in many respects an exceedingly valuable contribution to our knowledge of the curious
subject of color-blindness, -first, because it is the only clear
and consecutive account of that affection which has yet been
given by a party affected in possession of a knowledge of




46               COLOR-BLINDNESS:
what has been said and written on it by others, and of the
theories advanced to account for it, and who, from general
education and habits of mind, is in a position to discuss his
own case scientifically; and, second, for the reasons the author himself alleges why such a person is really more favorably situated for describing the phenomena of colorblindness than any normal-eyed person can possibly be. It
is obvious that on the very same principle that the latter considers himself entitled to refer all his perceptions of color
to three primary or elementary sensations,- whether these
be red, blue, and yellow, as Mayer (followed in this respect
by the generality of those who have written on colors) has
done, or red, green, and violet, as suggested by Dr. Young,
reasoning on Wollaston's account of the appearance of the
spectrum to his eyes, - on the very same principle is a person in Mr. Pole's condition, or one of any other description
of abnormal color-vision, quite equally entitled to be heard
when he declares that he refers his sensations of color to two
primary elements, whose combination in various proportions
he recognizes, or thinks he recognizes, in all hues presented
to him, and which, if he pleases to call yellow and blue, no
one can gainsay him; though, whether these terms express
to him the same sensation they suggest to us, or whether his
sensation of light with absence of color corresponds to our
white, is a question which must forever remain open
(although I think it probable that such is really the case).
All we are entitled to require on receiving such testimony is,
that the party giving it should have undergone that sort of
education of the sight and judgment, especially with reference
to the primitive decomposition of natural and artificial colors, for want of which the generality of persons whose vision
is unimpeachably normal appear to entertain very confused
notions, and are quite incapable of discussing the subject of
color in a manner satisfactory to the photologist.
" That Mr. Pole's vision is dichromic, however, there can
be no doubt. If I could ever have entertained any as to the
correctness of the views I have embodied of the subject in
that epithet, after reading all I have been able to meet with
respecting it, this paper would have dispelled it. That he
sees blue as we do, there is no ground for doubting; and I
think it extremely likely that his sensation of whiteness is




ITS DANGERS AND ITS DETECTION.


47


the same as ours. Whether his sensation of yellow corresponds to ours of yellow or of green, it is impossible to
decide, though the former seems to be most likely."
We thus see that the color-sense of the colorblind may be described as follows: The red-blind
sees all objects of this color of a darker hue than
they are. The same of the green-blind as to
green. Both confound these colors with each
other and gray. A mixture of white and black in
proper proportions, to represent the luminosity of
any shade of red or green, will give the color-blind
the same sensation as that shade. The violet-yellow-blind will do the same in reference to all colors
containing either of these two. Violet-blindness is
so extremely rare, and not causing danger on land
or sea, we may omit special discussion of it.
Great misunderstanding of the color-blind's sensation has arisen from the natural lack of knowledge
and appreciation of composite colors. Purple, or a
combination of red and violet, or blue, is rarely
otherwise spoken of than red in popular language,
except when the commercial name " magenta " is
used. The blue or violet in it the normal-eyed do
not think of, and none would class it with blue.
The color-blind, however, do not see the red in it
other than gray; but, as their vision is perfect for
violet, they see this in the purple, and so class it
with blue. Hence the general idea that the colorblind confound red with blue, the sky and a rose.
Pure red they never confound with blue.




48


COLOR-BLINDNESS:


CHAPTER VI.
COLOR-BLINDNESS FROM DISEASE OR INJURY.
COLOR-BLINDNESS is a congenital defect, and, as
will be later shown, incurable. It is not connected
with any special color of the eyes, or the humors
within the eyeball. The color of the eye depends
on the more or less pigment in the iris. The back
of this little screen is covered with black pigment,
preventing light passing through it, so that its
color can have no effect. The ocular humors of
a color-blind person have been found exactly the
same as the normal-eyed. Whether color-blindness is caused by some defect in the recipient organ,
the retina, or the perceptive organ, the brain, or
both, is not yet decided; and I need not discuss
the question here.
It is of more importance to know and remember
that a similar condition as to blindness to color is
caused by certain diseases of the eye or brain.
Ophthalmic, surgeons have long known that a loss
of chromatic sense was associated with a peculiar
form of atrophy of the optic nerve, which is
hereditary. Certain constitutional diseases, also,
cause color-blindness. In some affections of the




ITS DANGERS AND ITS DETECTION.


49


eye alone, portions of the retina become colorblind. As with simple congenital color-blindness,
the power of form-perception, in chromatic loss
from disease, may be retained.
Tobacco and alcohol, either alone or together,
may finally cause color-blindness. The warnings
of ophthalmic surgeons have been too little heeded
on this point. The loss of color-perception is
often overlooked, as the loss of form-perception
most troubles the person affected. Excessive
smokers and drinkers amongst railroad employds
and sailors may become color-blind when their eyesight is still good enough for them to retain their
positions, in which perfect color-perception is also
needed.
Color-blindness is caused also by accidents, QLd
especially by those accompanied with excessive jar
and shock, as on railroads. There are many wellauthenticated cases on record where normal colorperception was known to exist before the accident.
Professor Wilson reports a physician who was
thrown from his horse, and suffered great cerebral
disturbance. On recovering sufficiently to notice
distinctly objects around him, he found his perception of colors weakened and perverted, and has
since continued so. Flowers have lost more than
half their beauty for him; and he still recalls the
shock which he experienced on first entering his
garden, after his recovery, at finding that a favorite
damask rose had become in all its parts,-petals,
leaves, and stem,-of one uniform dull color, and
that variegated flowers, such as carnations, had
lost their characteristic tints.




50


COLOR-BLINDNESS:


Dr. Favre reports several interesting cases of
temporary color-blindness from injury, and says, -
" The majority of cases of traumatic color-blindness are
very analagous to congenital natural chromatic deficiency.
Railroad employes and sailors are certainly amongst those
who are most exposed to wounds and contusions. The large
majority of such are habitually or occasionally charged with
the observation or transmission of orders given by colored
signals. Railroad officials and naval officers ought therefore
to have their attention called to the circumstances which
may at a given moment and for a certain time deprive an
engineer, a stoker, a conductor, a pointsman, a station-master, a guard, a sailor at the helm, a lighthouse-keeper, a signal-man, or a coast-guardsman, of their correct judgment of
colors."
In illustration of color-blindness from disease, I
will mention Dr. Hay's case: A young woman aged
twenty had cerebral trouble, and, with some loss of
sight, considerable loss of color-perception. When
asked whether she could see the figure on her dress,
which was a calico one with red spots, she replied,
"Yes, I see the brown spots."    It was ascertained
she could distinguish forms, even of small size,
with accuracy; but her perception of colors was
exceedingly imperfect. Repeated and careful investigations during this and on several subsequent
occasions showed that the only colors she knew
with certainty were yellow and blue.     Nearly all
other colors she termed brown, or hesitated to
name, designating, however, their shades or intensity of color accurately. Thus a deep red she
called a dark brown; a bright green, a light brown;
and a very pale pink, a very light shade of brown.
She was not congenitally color-blind, and, after
some months of treatment, recovered her form and
color perception perfectly. She resembled a redblind person whilst suffering from her disease.




ITS DANGERS AND ITS DETECTION.


51


Tyndall reports a case of Mr. 'White Cooper's,
which, as it contains a word of warning, and is besides very interesting, I will give at length:
"1 The sufferer was a sea-captain, and ten or twelve years
ago was accustomed, when time lay heavy on his hands, to
occupy it by working at embroidery. Being engaged one
afternoon upon a piece of work of this description, and anxious to finish a flower (a red one, he believes), he prolonged
his labors until twilight fell, and he found it difficult to select
the suitable colors. To obtain more light he went into the
companion, or entrance to the cabin, and there continued his
needle-work. While thus taxing his eyes, his power of distinguishing the colors suddenly vanished. He went upon
deck, hoping an increase of light would restore his vision.
In vain. From that time to the present he has remained
color-blind. Berlin worsted, with which he had been accustomed to work, he at once and correctly pronounced to be
blue. Ile had a keen appreciation for this color, and never
made a mistake regarding it. Two bundles of worsted
- one a light green, and the other a vivid scarlet - were
next placed before him. Hle pronounced them to be both of
the same color. A difference of shade was perceptible; but
both to him were drab. A green glass and a red glass were
placed side by side between him and the window: he could
discern no difference between the colors. A very dark
green he pronounced to be black; the purple covering of the
chairs was also black; a deep red rose on the wall of the
room was a mere blotch of black; fruits, partly of a bright
red and partly of a deep green, were pronounced to be of
the same uniform color. A cedar pencil and a stick of sealing-wax placed side by side were nearly alike. The former
was rather brown; the latter, a drab. Electric light through
a green glass, allowed to fall on a screen, gave him no
color; but only that portion of the screen was a little less intensely illuminated.
"Capt. C. was assured, that, previous to the circumstances related, he was a good judge of colors; so that, pronouncing on any color, he has an aid from memory not
usually possessed by the color-blind. Indeed, he had an
opportunity of reviving his impression of red. A glass of




52               COLOR-BLINDNESS:
this color was placed before his eyes while he stood close to
the electric lamp. On establishing the light, he at once exclaimed, ' That is red I' He appeared greatly delighted to
renew his acquaintance with this color, and he declared he
had not seen it for several years. The glass was then held
near the light, while he went to a distance: but in this case
no color was manifest; neither was any color seen when a
gas-lamp was regarded through the same glass. The intense action due to proximity to the electric light appeared
necessary to produce the effect.  Capt. C.'s interest in
this experiment was increased by the fact that the Portland
light, which he has occasion to observe, has been recently
changed from green to red; but he has not been able to
recognize this change. The fare in the fore-cabin of a
vessel of his own, which he now commands, happens to be
sixpence; and he is often reminded by the passengers that
he has not returned their change. The reason is, that he
confounds a sixpence with a half-sovereign, both being to
him of the same color. A short time ago he gave a sovereign to a waterman, believing it to be a shilling."
Mr. Haynes Walton says, -
" A few years ago I was investigating color-appreciation,
and the first instance of the acquired defect that came to
my knowledge was in the person of an engine-driver. This
man confessed, after an accident through his not distinguishing the red signal, that he had gradually lost his colorpower, which had been perfect; and so sensible was he of
his loss and its disadvantages, that, before the accident, he
had determined to give up the situation. The manager of
the company, who told me the circumstance, assured me
that this driver had been carefully examined but a few years
back, and passed as possessing perfect sight. Does not this
show that those who are to be trusted with color-signals
should be periodically examined? "
We have thus seen that there is a condition
wholly resembling congenital color-blindness,
caused by disease or accident, and that it may be
recovered from when the results of disease or accident pass away. This must be remembered, as




ITS DANGERS AND ITS DETECTION.    53
color-blindness, when congenital, is incurable. To
the ophthalmic surgeon color-blindness is a recognized symptom of certain affections. This is a
question discussed in ophthalmic literature, and
out of place here further than I have introduced
it. The abuse of alcohol and tobacco is too common not to render possible color-blindness from
this cause among railroad employds and sailors,
a point at least to be remembered.




54


COLOR-BLINDNESS:


CHAPTER VII.
COLOR-BLINDNESS HEREDITARY.
LIKE all other congenital defects, color-blindness is hereditary, which explains the large ratio
of color-blindness individual observers have found
when happening to include one or more colorblind families in their statistics. In 1845 Dr.
Pliny Earle reported the color-blindness of five
generations of his family as follows:Of the first he knows nothing as to their colorblindness.
Second: of seven brothers and eight sisters,
three-~-rothers had the defect. One was Dr.
Earle's grandfather.
Third eneration, -children of the grandfather,
-- tee broters and four sisters: no one imperfect.
Four     an,       -first family of five brothers
an four sisters: two brothers color-blind.
Second family of one child (girl): normal colorperception.
Third family of seven brothers: four had colorblindness.
Fourth, not reported.




ITS DANGERS AND ITS DETECTION.


56


Fifth family of three brothers and seven sisters:
all perfect vision.
Sixth family of four brothers, five sisters: two
of each sex color-blind.
Seventh family of two brothers, three sisters:
the two brothers color-blind.
Eighth family: no issue.
Ninth family of two sisters with normal colorperception.
Seventeen of these people of the fourth generation are married, and have fifty-two children.
Many of the latter are very young (1845); and,
as the defective perception has hitherto been detected in but two of the families, Dr. Earle places
these alone on the list for the fifth generation. In
one of these families of three brothers and three
sisters, one of the brothers has the defect; and in
the other a male, an only child, is similarly
affected. We have therefore, in these thirty-two
males, eighteen color-blind. Of the twenty-nine
females, two are color-blind.
The overleaping of one generation by the hereditary peculiarity of vision is satisfactorily shown,
since it appears that there are no cases in the
third generation. Furthermore, in the cases of the
two males of the fifth generation, it will be perceived that neither parent nor grandparent had
the defect; so that there was an interval of two
generations between the manifestations of that
defect.
Dr. Earle regrets he is unable to give me a further report of his family to this time (December,
1878).
Such methods of testing as are now only consid



56


COLOR-BLINDNESS:


ered to be absolutely certain would, perhaps, have
revealed varying degrees of color-blindness in other
members of these families.
The first case ever reported, the shoemaker Harris, had three brothers color-blind also, whilst two
other brothers and a sister were free from the defect. Dalton had a brother color-blind like himself, another brother and a sister normal-eyed. In
one of Dr. Nichols's cases the defect was derived
from the maternal grandfather, some of whose
brothers were also color-blind.    In fact, hardly
any of the older cases reported did not show that
it was a family peculiarity. Wartman says, -
" With respect to affinity, there are some color-blind no one
of whose kindred exhibits this anomaly of vision. Others
have, so to speak, inherited it from their father or their
uncle, either paternal or maternal (without, in the latter
case, the aunt participating in it). Lastly, it is not rare to
find brothers, several of whom are color-blind, without their
being all necessarily so. The sisters are almost always
privileged."
We must, however, remember that, so long ago
as when Wartman wrote, this defect was rather
regarded as a scientific curiosity, not particularly
affecting practical life. The blood-relatives of a
color-blind would therefore rarely be hunted up
and tested.
Cunier, moreover, in 1838, reports the case of a
lady who was color-blind. Her mother and two
sisters were the same. Her brother was free from
the defect. The lady had six children, - one son
not color-blind, and five daughters affected like herself. The oldest daughter had four children, two
of them (girls) color-blind. The second daughter
had a boy and a girl, the latter color-blind. The




ITS DANGERS AND ITS DETECTION.


57


fourth daughter unmarried. The fifth left a boy
myopic, but not color-blind. We thus have the
remarkable instance of color-blindness appearing
only in the females of a family for four generations. Dr. Ph. Hochecher says," Many observers have shown color-blindness to be hereditary. I am not the only color-blind in my family. Three
of my mother's brothers are so, one of my cousins, and a
nephew. The same is the case with one of the students,
whose case I report. He is color-blind, his mother, and his
mother's brother, as was-also his brother, now dead."
Heredity was frequently very marked, known,
and reported on among the many people who replied to Professor Wilson's inquiries. He even
says," No fact is better ascertained than that color-blindness
clings to certain families, and is hereditary. With few exceptions, every one of the parties whose cases I have specially recorded in this paper has near relatives as color-blind
as himself. It seems, indeed, a safe estimate, that every.decided case of color-blindness implies the existence of
another case of equal or similar severity in the person of a
relative; so that the numbers I have given as representing
the proportion of color-blindness in the community may be
fairly doubled."
My own experience agrees with Professor Wilson. Few of the adult color-blihd whom I have
tested did not know of some blood-relative similarly affected. It has been found prevalent with
the Jews, among whom intermarriage and consequent hereditary peculiarity is very frequent.
Professor Horner of Zurich has given the data
on which he based the law of transmission of
color-blindness, and they are of such value in reference to heredity, that I introduce them here




58


COLOR-BLINDNESS:


with the remarks accompanying his original article. He says, -
"The hereditariness of color-blindness has been long
known. Ribot and Darwin speak of it, as also that it is
more frequent in men than women. As I have had opportunity of being familiar with very accurate pedigrees, which
illustrate a definite law, I will give the results of these genealogical researches.
" The first family I became acquainted with some years
since. In the following Table I., the male descendants are
marked with M, and the female with W. The generations
go from A to G. The letter of the particular generation
stands beside the letter for the sex. To simplify the tables,
the unmarried daughters, and the brothers and sisters whose
descendants could not be followed, are omitted. I would,
however, expressly say that this omission only affects the
result in that the law appears more marked, not that an
exception to it is thereby concealed. For instance: if, in
generation D, several unmarried normal-eyed daughters, in
generation G some normal-eyed sons not yet married were
included, it would have further illustrated the law, but have
rendered the scheme more difficult to express in print.
"From the youngest generation H, the tree is quite certain up to generation C. I have the proofs of this from
those who were living in the commencement of the eighteenth century. From here upwards the conclusion as to
the common origin is hypothetical. We know nothing of
the color-blindness of A. He was the father of two daughters, who have red-blind sons. From the evident law among
the descendants, it is fair to conclude that the mothers were
not color-blind, but the grandfather was. At any rate, the
table, even if we omit the upper row as hypothetical, is of
much interest, and plainly shows, -
" 1st, That there were no color-blind girls.
"2d, That color-blind fathers had normal-eyed sons.
"3d, That color-blind sons had normal-eyed mothers.
"4th, That the seeming exception in generation F, where
a color-blind father had a color-blind son, is explained as
still in conformity with the law when we recall that the
mother, color-blind, was the daughter of a color-blind father,
and we have the descendants of two color-blind.




ITS DA-NGERS A.ND ITS DETECTION.


59


TABLE i.


*j.- ~j  I
re
I M
co    2
0- -- -- --
*.


*           *
5,
/
*~
U
*.   -
*        0-r
*          0 ---
U3  ~.L  0: U


EXPLANATION.- The star (*) denotes those who were color-blind.




60          COLOR-BLINDNESS:
TABLE II.       o0
M*
o                 o
X                 fi....
CD.of                ^  ~ \.,
o          o=>fi..................  0
00..
0
\         *
C.\         s\    C) -






ITS DANGERS AND ITS DETECTION.


61


" 5th, The general law is, therefore, 'that sons of daughters whose father was color-blind are most likely to be the
same, although not without exception (vide H); or, colorblindness is transmitted in the revertible type from grandfather to grandchild.'
"I have become acquainted with another family tree
which gives, although to a lesser extent, the same type. I
place it without comment with the other, calling attention
to only one interesting fact; namely, a jump of two generations. The first daughters of generation B bore only girls,
whose sons followed their great-grandfather's type. In this
smaller pedigree it is seen that in generation C and D the
transmission to the grandchildren is not absolute; so that it
is the complement of Table I."
Cohn found, among his one hundred color-blind,
three times the father red-blind, fifty-six times the
parents normal-eyed; in fourteen cases the brothers color-blind; once the father and three sons. In
no case were all the children color-blind. A colorblind father had seven children, all normal-eyed;
but the mother's brother, a cousin of the mother,
and all the sons of this cousin's only sister, colorblind (none of the daughters).
Dr. Magnus says," The hereditariness of color-blindness has been known
as long as the defect itself. All who have seen many colorblind will have often noticed that it was in their mother's
family that other cases were found. I have frequently been
assured that this or that cousin on the mother's side was also
color-blind; and, now and then, that a more distant relative
of the mother had also color-blind sons. In view of Homer's
law, this is readily explainable; and this peculiar law is all
the more interesting since we find that it is the same in reference to the heredity of other physiological abnormities or
defects. For instance, we know that in families the tendency to bleeding is similarly handed down, and also, as Dr.
Pagenstecher has recently shown, night-blindness. It would
seem as if this law of heredity had a more general applica



62               COLOR-BLINDNESS:
tion. It would be most valuable if family physicians, who
know and observe their patients' families for several generations, could interest themselves in carefully elucidating the
extent of this important law.
"Naturally this law does not exclude the possibility of
other ways in which color-blindness may descend. In some
cases I have with certainty found that a color-blind father
begat color-blind sons. I remember now two cases in which
a color-blind father had two color-blind sons."
In a later publication Dr. Magnus says, -
" The effect of heredity is very marked in my examinations.  Of ninety-five color-blind, whose families I could
inquire about in reference to this point, I found it in fortytwo. Five times the parents were normal-eyed, but the
grandfather color-blind, and in three of these cases the
father of the mother. Riite, in 1845, said, 'The defect is
hereditary, and, peculiarly enough, rather through the women than the men. For example: the maternal grandfather
transmits to the grandchildren.'  A very interesting proof
of this law I have lately received by letter from Professor
Valentine of Berne, Nov. 5, 1878, who writes, 'I naturally
can have no opinion as to Homer's law. I only know one
case near me which supports it. Professor F., formerly
here, was color-blind: his children are not. He had five
daughters, who are all married. Their children, so far as I
could trace, are mostly color-blind."'
Again Magnus says, -
" I have also among my color-blind found with certainty
six times that the maternal relatives were color-blind, and
it was inherited through them. In three of these cases it
was the mother's brother, maternal uncle, who was colorblind. Two sisters each had a color-blind son, one of whom
I tested. Two cousins, daughters of two sisters, each had
a color-blind son. I do not, therefore, think it too hasty
to say that the color-blind inherits his defect very frequently
from his mother's family. She will be normal-eyed, and
transmit color-blindness to her sons, but not to her daughters."
Besides the very many times I was told by those




ITS DANGERS AND TS DTECTION.       63
I tested of some relative being supposed to be
color-blind, I had direct testimony from my own
observation, or testimony of a character I could
depend upon, in the following instances: Sixteen
times brothers being color-blind; once, father and
son; maternal grandfather and two grandchildren,
boys, - three sisters not so; maternal grandmother
and grandson; mother and son; male cousins
twice; twin brothers red-blind; of two brothers,
one red, the other green blind; a lad, his greatuncle and grandfather; three brothers out of five
color-blind, but none of their children; two brothers and maternal uncle; three brothers out of
four color-blind, the other too young to test.
I have thus called especial attention to colorblindness being hereditary, as it has a direct bearing on the important question of the frequency of
the defect, upon which of course depends the comparative danger to the community at large.




64


COLOR-BLINDNESS:


CHAPTER VIII.
PHYSICAL PECULIAIRTIES CONNECTED WITH
COLOR-BLINDNESS.
I HAVE spoken of the improbability of the color
of the iris or hair having any connection with
color-blindness other than accidental. My own
observations on more than 430 color-blind induce
me to discard this at present from further thought.
In this Cohn agrees with me. Where light hair
and irides are in the majority in the community,
they will be so found among the color-blind.
Magnus recorded 48 among 93 color-blind with
black, brown, or dark hair, and 45 with blonde;
28 had yellowish-brown or yellowish-gray eyes,
and 65 blue or bluish-gray. Seebeck, in 1837,
found 10 of his 12 cases had blue eyes, but wisely
remarks that it is probably simply due to the fact
that such are most frequent among all northern
nations. There seems to be nothing gathered
from testing the refraction or accommodation of
color-blind eyes. The results are those to be
obtained from the examination of the same classes
as the color-blind belong in. The visual power is
apparently the same as with the normal-eyed; but




ITS DANGERS AND ITS DETECTION.


65


I have seen very extraordinary visual power of
form associated with color-blindness. As to the
ear and musical power, I can say nothing from my
own observation. Magnus could obtain nothing
decisive on this point.
In respect to parental relationship, I can only also
quote Magnus and Cohn. The former, amongst his
94 color-blind, found but six times the parents
related, - always cousins. This point is worth
studying; but deductions should be made with
great caution. Cohn also found six times the
parents related. Five times they were cousins. In
one case the father had no color-blind children by
a wife not related to him. His second wife was
his cousin (their mothers being sisters), by whom
he had two color-blind sons.
There is one other physical peculiarity which
has been connected with color-blindness; and that
is a contraction of the forehead, and consequently
of the anterior lobes of the brain. Niemetscheck
measured the distance between the pupils of four
color-blind, and found it to be 49, 50-54 mm.
From this he deduced the idea that the brain mass
anteriorily was proportionally smaller; and here
was where the phrenologists placed color-perception. The idea was supported by Aubert; but
Dr. Cohn measured his one hundred color-blind,
finding the distance between the pupils thus:
54-56 mm. in 20 scholars 9-13 years old.
5862 miun. in 60 scholars 9-14 years old.
63-66 mm. In 18 scholars 12-22 years old.
67 mm. in a color-blind 67 years old, and 70 mm. in one
40 years old.
His conclusions, therefore, are that, "had Nie



66


COLOR-BLINDNESS:


metscheck found protrusion of the eyeballs in his
cases, he could as well have connected it with
color-blindness."
Professor Pfluiger, in Berne, measured the distance between the pupils of 1,846 normal-eyed
children, and found in those between 7-14 years
this to be 54-59 mm.; in those between 15-19,
to be 59-62 mm.; also, in older students between
20-22 years, he found it was 61-63 mm. Cohn
therefore claims rightly that his color-blind had
rather a greater distance between the pupils than
the normal-eyed of the same age: hence the theory
of Niemetscheck is not true.
Professor Holmgren also reports in 1878 his
measurements of the distance between the pupils
of 100 color-blind. He employed an instrument
he had specially arraned for this purpose.       He
also finds that there is n6 measurement of this
kind characteristic of the color-blind.
Professor Wilson said in his book, -
" I have to notice a singular expression in the eye of certain of the color-blind, which may assist in their detection.
It is difficult to describe it, and it is wanting in well-marked
cases. But various of the color-blind, whose cases I have
described, have presented a peculiarity of look, which
others have recognized on their attention being drawn to it.
In some it amounted to a startled expression, as if they
were alarmed; in others, to an eager, aimless glance, as if
seeking to perceive something, but unable to find it; and, in
certain others, to an almost vacant stare, as if their eyes
were fixed upon objects beyond the limit of vision. The
expression referred to, which is not at all times equally pronounced, never altogether leaves the eyes which it seems to
characterize."
In the appendix he also says, -
" I have had the opportunity Qf observing it somewhat




ITS DANGERS AND ITS DETECTION.


67


particularly in four gentlemen not relatives, in two of whom
it was readily recognized by others. All the parties referred
to have healthy eyes, and excellent vision for every thing
but color. One has an absent, anxious glance, with something of the expression which amaurosis gives, only the
pupil is small. One has a startled, restless look. The
other two have an eager, prying, aimless air. The character common to them all, and to the other cases I have seen,
is this aimlessness of look. Macbeth's reference to Banquo's ghost, -
'Thou hast no speculation in those eyes
Which thou dost glare with,' -
very happily expresses the peculiarity which I find so difficult to define. It has not, however, in most cases, any thing
repulsive about it. The majority of those I have seen presenting it would be described as having fine eyes. In one,
the wistful, somewhat melancholy, but pleasing expression
of his eye, had attracted my attention long before I knew
that he was color-blind."
I can recall something of what Dr. Wilson describes in reference to two or three of my colorblind acquaintances, but, on the contrary, not at
all in reference to others. I recognize his difficulty
of describing just what it is. I doubt if I should
have noticed it, or at least connected it with colorblindness, except for his remarks in reference to
it. Had he spoken of such a look or peculiar
expression on the part of the color-blind when
being examined, I could corroborate it from my
experience with both adults and young persons.
I have now and then made my diagnosis correctly,
from a peculiar dazed, half-anxious expression of
the face and eyes of a looker-on awaiting his turn,
as if they were called upon to do something unusual, and sought or expected further explanation
than that given the normal-eyed. I do not, of




68


COLOR-BLIN-DNESS:


course, mean the natural nervousness of those
conscious of some defect; but of those-color-blind
who had no idea any thing was wrong with their
chromatic sense, and who often proved difficult to
convince. I believe no other observer than Professor Wilson has remarked on or recorded any
thing of the kind.
As to nationality, I have but to say, that, in our
mixed population, nearly every European nation
is represented. An opinion was expressed long
ago, that the defect did not occur in the colored
race. My opportunity of testing them has been
but very small. Among 102 colored schoolboys
I found 2 color-blind; among 94 colored schoolgirls, none.
Whilst this volume is in press I have heard from
Dr. Swan M. Burnett of Washington, D.C., who
has had an opportunity I could not obtain. He
has tested, by Professor Holmgren's method, 1,359
colored schoolboys, and found 22 color-blind (or
1.6 per cent); also 1,691 colored schoolgirls, finding
only 2 color-blind (or 0.11 per cent). This smaller
percentage among the boys may be due to various
causes aside from the difference of race. Moreover, larger numbers may entirely change it.




ITS DANGERS AND ITS DETECTION.


69


CHAPTER IX.
FREQUENCY OF COLOR-BLINDNESS IN MAES.
As the magnitude of the danger depends, of
course, on the frequency of the defect, it becomes
important to know in what proportion of the community color-blindness is likely to occur. Very
variable statistics are given by different observers,
depending largely upon the methods of testing;
the more thorough and scientific these latter are,
the greater being the number of color-blind individuals found. Mistakes of excessive ratio reported are now better understood and avoided,
since we know color-blindness runs in families,
and is hereditary. An observer might thus find
10 out of 40 individuals examined color-blind.
Let us glance at the statistics, such as they are,
reported by the earlier observers. Dalton found
8 to 12 per cent; Professor Pierre Prevost, 3 to 5
per cent. Professor Kelland of the Edinburgh
University found, among 151 students, 3 "'thorough Daltonians," and several less well-marked
cases. Wilson again found 2 among 20 students,
1 among 47 other students; on the Edinburgh
police, five among 158. Dr. Rowe, at the Morning



70


COLOR-BLINDNESS:


side Asylum, found 5 among 42 male attendants.
These I quote from Wilson. Seebeck found 5
color-blind among 100 students. Professor Allen
Thomson met with the same result as Dr. Wilson,
as also D'Hombre-Firmas in France, and Professor
Dove in Berlin. Dr. Wilson also examined a
large number of soldiers, who, together with those
above spoken of as tested by him, amount altogether to 1,154 persons. Amongst these all, 65
were color-blind, an average of 5.6 per cent, or
1 in 17.7. The red-blind were most numerous
throughout all these. This proportion has been
now admitted by Professor Helmholtz. Wilson
said, in 1854,-," The statistics of color-blindness are as yet very imperfect, and do not' include females; but there is every reason
to believe that the number of males in this country (England) who are subject in some degree to this affection is not
less than 1 in 20, and that the number markedly colorblind-i.e., given to mistake red for brown, brown for green,
purple for blue, and occasionally red for black - is not less
than 1 in 50. We may thus, according to our present
knowledge, regard two in every hundred of the community
as seriously defective in their perception of color."
Dr. Goubert estimates 1 in 25 color-blind.
Dove, in his memoir of 1872, gives the following
figures: Among 860 men, there were 40 colorblind, 4.65 per cent, or 1 in 21.5; among 611
women, 5 color-blind, or 0.82 per cent, or 1 to 122.
Among 1,016 scholars at the Lyons Lyceum, he
found 16 color-blind for red and green on a visit
made in April, 1877.
The last report of Dr. Favre, of the Lyons
Mediterranean Railroad, gives the results of examinations of railroad employ4s since 1855. It




ITS DANGERS AN) ITS DETECTION.


71


shows also how more careful tests discover a
greater proportion of color-blind persons. Dr.
Favre, up to 1855, had examined about 5,000 candidates for railroad-work, and rejected more than
50 for being red-blind. He had not, unfortunately,
kept accurate records. From 1855 to 1864 he
noted 8 color-blind only, which number does not
correspond with the number of men examined.
From 1862 to 1872, among 1,196 persons, he refused 14 color-blind who could not tell red. From
May, 1873, to July, 1875, his examinations were
more particular and exact; and he found, among
1,050 persons seeking railroad employment, 98
who made decided blunders, or hesitated: 10 were
refused for being red-blind. His new series since
1875 comprises 600 examinations: the results of
these he has not yet sent me (January, 1879).
728 men already in employment were examined in
1872-73. More than one-third of these had been
previously tested for color, and the red-blind eliminated. Of these 728, 42 either made mistakes or
repeated hesitations. Among 224 conductors examined by Dr. Favre and M. Git, 14 were found
decidedly color-blind. In 1874 he found 4 colorblind among 75 office-clerks; the same year, 24
among 65 firemen at the Perrache gas-works. At
the Ouillins works, among 148 workmen whom
he examined in August, 1877, 82 told the five
elementary colors without error or hesitation; 56
either hesitated or made mistakes. May 7, 1877,
among 155 students at the veterinary school at
Lyons, Dr. Favre found 19 hesitate or make mistakes. Examining, with Capt. Bellecour, 268 subofficers and men of the Sixteenth line, he found




72


COLOR-BLINDNESS:


105 color-blind or color-deficient. Among 138
men of the Twenty-second, Twenty-third, and
Ninety-ninth line, M. Paul Guillot found 37 colorblind. Lieut. Gallet of the Twenty-sixth Artillery, in garrison at Mans, examined 116 young
soldiers, and found 32 who hesitated or made mistakes on a color-scale of 15 shades. Lieut. Lautheaume found 40 color-blind among 132 men of
the train of the Twenty-sixth Artillery. The
average among this series of 654 young soldiers
was 32.72 per cent. Dr. Mourand, among 200
men of the Lyons station, found 7 color-blind.
Dr. Favre says his colleague must have noted
only the most marked cases.
Dr. Feris, in his pamphlet, and more recently in
a communication to Dr. Favre, reports having examined 775 officers and sailors, amongst whom he
found 75 color-blind: 19 wholly confounded red
and green. The average of this series is 10 in 100.
Of all the adults Dr. Favre examined, the average
was 16.84 to 100. He says, —
" The results will vary greatly, being dependent on many
circumstances and peculiarities I shall hereafternotice; but
we may be assured, that in France the color-blind amount
to ten in one hundred of the adult males.... The study of
color-blindness interests at least a tenth of our population
(France). This very large proportion gives us the measure
of the chances of error the color-blind run in the various
industries where good color-perception is necessary or useful. It does not, of course, give us an exact idea of the
chances of accident at sea and on railroads, on account of
the accessory circumstances which aid the color-blind in his
embarrassment; but it shows us plainly how numerous the
chances are."
Dr. Favre also reports the results he received
from a friend in Algiers, who tested, with great




ITS DANGERS AND ITS DETECTION.


73


care, 693 persons, and found as follows: Among
203 Kabyles, 5 cases of color-blindness; in 95 Biskris, 4 cases; in 81 negroes, 1 case; in 23 Jews, 1
case; in 15 Spaniards, none; in 62 Italians, 1 case;
in 15 Mozabites, none; in 12 Maltese, 1 case; in 8
Tunisians, none; in 19 Europeans, 1 case, -in all,
19 cases among 693 persons examined, or 2.75 per
cent.
Dr. A. Lederer has lately found 63 color-blind
persons amongst 1,312 men of the Austrian navy,
or 4.8 per cent.
Dr. Fontenoy found 31 color-blind out of 1,084
railroad employds of Denmark, or 2.87 per cent.
Professor Donders of Utrecht, Holland, found,
among 2,300 railroad employds, 152 color-blind.
Dr. Stilling of Cassel, Germany, found, out of
400 railroad employds, 6 per cent color-blind.
Dr. Krohn, in Finland, found, among 1,200 railroad employds, 60, or 5 per cent color-blind. These
and other reports of railroads I shall return to
hereafter.
Professor Quaglino of Milan, Italy, writes me
(Aug. 11, 1877)," It has been generally believed that color-blindness is
more rare in Italy than in Germany, England, or France;
but I much doubt this, as there has been little research
among us, and I think that a large amount will be found
were it carefully looked for."
Dr. Daae of Kragero, Norway, found, amongst
205 schoolboys, 4.88 per cent color-blind.
Dr. Cohn found, among 2,429 schoolboys of
Breslau, 95 or 4 per cent color-blind.
Dr. Magnus found, among 8,273 Breslau schoolboys, 3.5 per cent color-blind.




74


COLOR-BLINDNESS:


Professor Holmgren, in Sweden, found, among
32,165 males, 1,019, or 3.25 per cent color-blind.
Dr. Minder of Berne, Switzerland, found, among
1,429 males, 95, or 6.58 per cent color-blind.
To recapitulate the larger numbers and more
recent examinations:
0 0, i
OBBRVERS.          Place.            Q              Position in Life.
Dr. Fontenoy. Copenhagen.1,084      31 2.87   Railroad employes.
Prof. Donders. Utrecht..   2,300  152  6.60     "        A
Dr. Krohn.. Finland..   1,200   60  5.00     "        "
Dr. Minder. Berne..   1,429   95  6.58  Schools and various.
Dr. Daae.       Norway..    205     -  4.88  Schoolboys.
Dr. Cohn.. Breslau.   2,429   95 4.00        "
Dr. Magnus..3,273       -  3.50       "
Dr. Stilling.Casel              400     -  6.00  Railroad employes.
Dr. von Reuss. Vienna..    800     -  3.50  Railroad employes.
Prof. Rl:mgren, Sweden            3,654  166 4.54   Scholars.
8,682                      300  3.45    "d
A 1,523                            47 3.08   Students.
i                         2,752   105 3.81   Orphan children.
c                          555    43  4.50  Young people.
7,953                            171 2.15   Railroad employes.
4,225                             94  2.22  Sailors.
1,851                      62 3.34   Soldiers.
"                       649   31 4.77   Mill-hands.
" "                         321    18 5.60   Prisoners and g'rds.
Dr. Jeffries. New England, 10,387     431 4.149 Teachers and sch'rs.
The following are the results in tabular form of
my own examinations:



E0
HQ
30
02


March,                    Completely.  PartialPOSITION OF PERSONS TESTED.                 A18pl    ber.-  Ages.    Red     reen   Color- Total CPe
1879.                   Blind. Blind.


Instructors and Students.
Several departments of Harvard University, Cambridge,
Mass.; Institute Technology, Boston, Mass.; Amherst College, Mass.; Brown University, Providence, R.I..
Teachers' and Students' State Art-School.....
Other adults...........


March,
June,
1878.


Boys of Public
Latin School.
English High School
Roxbury High School
Dorchester High School
Charlestown High School
West Roxbury High School.
Brighton High School
Phillips Grammar School
Eliot Grammar School
Quincy Grammar School
Brimmer Grammar School
Lawrence Grammar School
Rice Grammar School.
Dwight Grammar School
Sherwin Grammar School
Dudley Grammar School
Bigelow Grammar School
Andrew Grammar School
Lincoln Grammar School
Dearborn Grammar School
Comins Grammar School


Schoots or.Boston.
~..   *
~.*.  *
*   *.  *   *
*. *    ~
~*...
~*....
*   ~..
*.   *.....


1878.
1879.


1,021
32
31
415
433
80
38
47 207
22
20
682
774
575
606
877
595
633
434
472
807
366
629
464
334


10 to 17
G  I


18 years
and
upw'ds.


14 to 17
8to15yrs.
ds
~6
is
6c.S
4 4
I.I.S
di
Si
4 4
6.
it


22
8
10
4
24
20
19
19
21
12
13
16
13
19
5
26
19
16


12
3
7
3
1
-
18
2
9
2
7
2
5
1
1
1
2


12
1
2
5
3
1
3
1
4
6
7
4
9
2
4
1
2


22
10
}4
45
23
28
21
28
18
24
24
18
28
8
30
22
18


46   4.505
1     -
13    -


5.301
2.309
1.932
6.598
2.967
4.866
3.465
3.534
3.025
3.791
5.530
3.813
3.469
2.185
4.769
4.740
5.389


Total............      -     10,387      -       288      75      68         43.149




76


I6COLOR-BLINDNESS:


All these examinations were made by Holmgren's method with the colored worsteds, to be described later in this volume. The division into red
and green blindness of the first thirty-five hundred,
I am not as sure of as that of those afterwards,
for reasons I have stated in my last chapter. I
have followed Professor Holmgren, and my results
correspond very nearly with his and those of
observers who have also been governed by his
directions.
My work so far has been rather the collection of
statistics, and the dissemination of a knowledge
of color-blindness, than a study of the defect itself,
except in individual cases. I am, therefore, merely
presenting its frequency here, which can as well be
determined from school-children, since a person
born color-blind dies so.
My friend, Dr. Magnus of Breslau, from his
own and Professor Cohn's reports of their examinations of the school-children above quoted, concludes that color-blindness is more frequent as we
descend the social scale, and also more frequent
amongst the Jews. As to this last I was unable
to decide whether the schoolboys were Jews or
not. In regard to the former, - viz., the greater
frequency among the lower classes, -I was surprised to find this did not hold in our community
of mixed races, nor did it among the schools where
the race was more purely American. Parentage
I could not record; but, in a general way, I should
say the percentage would be as high or higher
among American-born children. My work has
satisfied me that we cannot draw safe deductions
from a few thousand examinations, but must pa



ITS DANGERS AND ITS DETECTION.


77


tiently wait till our lists contain enough to eliminate sources of error from inadequate data and, so
to speak, possible local causes.
I have made no column of violet-yellow-blindness, as, besides some very doubtful, I can but
report three cases; and these I have allowed to be
recorded under " partially color-blind."  These
three cases I carefully examined again, and found
that whilst the red-green perception was not, perhaps, perfect, - so that, on that account, they would
propably have been classed among the "t partially,"
-yet as to violet yellow they were wholly blind, as
shown by Holmgren's worsted test. In one case
there was reduced color-perception for all three
of the primary colors, - red, green, and violet. I
have no doubt, that, to many of my color-blind,
the spectrum would be more or less shortened at
the violet end. Many were too young to thus test,
and that, moreover, was not the purpose of my
work at the time of examination.
I should add here that I made no examination
or record of the exact visual power for form of the
color-blind I found, as it is wholly uncalled for by
this method of testing. They were teachers, students, or scholars at work with their eyes. Neither did I have to regard whether they were normal-eyed, old-sighted, near-sighted or over-sighted
(presbyopic, myopic, or hypermetropic), since we
need not correct errors of the refraction of the
eye when thus searching for color-blindness.
I have not given the percentage of the thirtyone "other adults," as some came to me suspecting
or knowing of their defect. There were, however,
only three of these. The others were accidental




78


COLOR-BLINDNESS:


examinations amongst acquaintances or patients
and employ6s. I omit also the special percentage
of the art-school.
The instructors and students of the colleges I
have added together, to better eliminate sources of
errors, as I did not examine all the students of any
one of these institutions.
In the statistical memoirs of the United States
Sanitary Commission, published in 1869, are the
only other examinations I know of made in this
country. The method of testing — viz., holding up
pieces of colored cloth, &c., and asking the names
of the color -was, of course, very crude and unreliable.  I, however, introduce the report here.
The compiler, Dr. B. A. Gould, says," Serious misunderstandings or calamities have been reported in the army, resulting from mistakes in the color of
green and red lights by officers of the signal corps, themselves not fully aware of their failing in this respect; and
cases have occurred when ludicrous and even disastrous results have followed the use of a badge of precisely the
wrong color."
Instructions were issued to test for color-blindness; and, in the reports received, "the descriptions of the irregularities manifested in distinguishing colors are, in general, neither complete nor
adequate, owing propably to insufficiency of the
instructions given." Among 8,831 white men,
161 were found color-blind, equal to 0.02. This
small ratio is, of course, due to the crude method
of examining, which would only detect the most
marked cases of color-blindness. Dr. Gould
adds, -
" Notwithstanding the incompleteness of the descriptions
returned, and the consequent inadequacy of the classifica



ITS DANGERS AND ITS DETECTION.


79


tion, the well-known fact is distinctly manifest, that the
most usual form of color-blindness is that which fails to distinguish between the green and red, and that the confusion
of colors sometimes embraces the other half of the spectrum, and sometimes its entire range."
The great variation in the ratio of color-blind
persons, reported by different observers, is readily
explained by differences in the accuracy of the
method of testing.
In testing color-perception by the sun's spectrum thrown on a white surface, the color-blind
observer will see the color he is deficient in over
a smaller surface.    Dr. Edward Rashlmnann, in
Halle, reports the test of 70 people with the sun's
spectrum. He found only 30 of them saw the
red normally: the others varied in their red-perceptive power. He tested only 20 as to the violet
end of the spectrum, and found remarkable shortening of the visible portion for this end also. He
noticed, besides, that, when the red end of the
spectrum was shortened, the violet was also reduced, limiting the spectral row of colors on both
ends.




80


COLOR-BLINDNESS:


CHAPTER X.
INFREQUENCY OF COLOR-BLINDNESS IN FEMALES.
IN an article written in December, 1877, on the
dangers of color-blindness, and published in the
Ninth Annual Report of the Massachusetts State
Board of Health, I stated,
"It has been frequently said that color-blindness was less
common among females than males. This is probably incorrect, and due to the fact that such a defect is of more importance with the female sex, and therefore more carefully
concealed. They have not been tested as males have; and
most likely future statistics, based on true methods of testing, will reverse the now quite general impression as to their
having better color-perception, and hence to be preferred,
where admissible, as railroad employes."
My doubt was also based upon the fact that we
then had no large number of reliable statistics to
prove the contrary, but more especially because
methods of testing for color-blindness in females
had been employed, calling upon the observed to
name colors shown, which females, from habit,
could unquestionably do with greater facility than
men; and hence fewer appear deficient in colorperception. Professor Wilson, in his " Researches
on Color-Blindness," says (p. 75), -




ITS DANGERS AND ITS DETECTION.


81


"I have no results to offer respecting the prevalence of
color-blindness among females. I have already stated my
conviction that it is rarer among them than among males;
but only an extended inquiry can show the amount of difference in this respect between the sexes."
In a note in his Appendix (p. 164), he adds, -
" Since the text was written, I have been informed of a
few more cases of color-blindness among educated women
in England. The general tendency, however, of my later
inquiries, as of my earlier ones, is to show that color-blindness is very much rarer among women than men."
Dr. A. Favre, in an article in the "Gazette
Hebdomadaire," Oct. 12, 1877, says, -
" We have tested very few adult females, from the difficulty of such examinations, but more especially because the
majority of women readily acquire an exact notion of colors,
and they do not belong to the professions where color-blindness is dangerous: hence they do not interest us more in an
industrial than a medical point of view. Among 236 girls
of four schools (three in Lyons, one in Paris), we found 8
children only who made serious mistakes; namely, 3.39 per
cent. In the ' salles d'asiles' and the infant-schools the errors
were as frequent among the little girls as boys."
It must be remembered that Dr. Favre reported
an enormous number of children of both sexes as
color-blind; but he tested them by asking the
names of the colors of objects held up before
them. He found, as may be readily imagined,
many of the youngest children of both sexes unable to answer correctly; whilst, among the older
children, the girls had naturally learned the names
of colors better than the boys. This, I think, is
all that his test proves, as I shall hereafter show.
In 1860 Dr. Henri Dor of Berne tested in Berlin
611 women, using a method similar to that of Professor Holmgren; namely, the sorting of colored




COLOR-BLINDNESS:


worsteds, with the result of finding only 5-or
0.82 per cent, or 1 in 122 - color-blind.      This
method does not call upon the -examined to name
a color; and the eye alone, not memory, guides
the hand. Its value is shown by the results it
gave. Perhaps these investigations of Dor should
have prevented my doubting the less frequent
occurrence of color-blindness in women than men.
They seemed, however, to stand somewhat alone,
and not sufficiently extended.
Professor Holmgren, in his recent work on colorblindness, touches on this point; and, as his experience renders what he says of special value, I
quote his remarks: -
" In drawing conclusions from the statistics of the examination of women hitherto made, we must first of all ascertain if the method of testing was such that the previous
occupation of the examined had not affected the results
obtained. For if the method was based on the principle of
asking the names of the colors of objects exhibited, and the
chromatic sense of the person examined judged by the reply,
then it is very evident that the proportion of color-blind will
appear less with women than men. Admitting that colorblindness is less common in women than men, we are by no
means justified in attributing this to their greater familiarity
or exercise with colors. If exercise can have any such influence, it cannot, as we have seen, cure the individual, but
rather affect the offspring, as employment insensibly affects
future generations. The laws of heredity are too little
known to allow us to indicate, or even conjecture, how this
takes place; but we do know with certainty that good qualities as well as defects are transmitted, and amongst the
latter we may include color-blindness. We believe, moreover, that the exercise of a sense may favorably affect
heredity, although it is difficult for us to prove this."
At the present moment observers in Europe are
testing this question of the relative color-blindness




ITS DANGERS AND ITS DETECTION.


83


of the two sexes. Their results, where Professor
Holmgren's method has been employed, are of
great value. A number of reports of this character
have come to my hand. Dr. E. Hansen of Copenhagen found none color-blind among 50 female
railroad emyloyds. Dr. A. Daae of Krager6, Norway, also used Holmgren's method with the worsteds in examining 413 school-children of both
sexes, from nine to fifteen years of age. Amongst
208 girls he found none color-blind, and only 5 with
imperfect color-perception. He says, -
"The better color-perception of the girls than the boys
was very marked. Is this because the girls have personally
more exercise with colors than the boys? If this is the
case, then we must assume that even very considerable degrees of color-blindness may be relieved by many years'
exercise. This is, however, not probable. It is more probable that the better color-perception which the female sex
has acquired and developed by many generations of handling
colored objects is essentially sexual, or only inherited by
the female descendants."
Since February, 1878, when I published an article on the incurability of congenital color-blindness, my experience with intelligent and educated
persons thus afflicted has fully substantiated what I
then said; namely, that ift has not been and cannot
be cured by exercise with colors. The color-blind
reported to me their futile attempts to do this, as
others, for instance, reported to Professor Wilson
years ago, and to Professor Holmgren more recently. Greater familiarity with, and more constant use of, colors on the part of females, seems
at first sight to explain their somewhat extraordinary exemption from color-blindness as compared
with males.   This does not, however, affect the




84


COLOR-BLINDNESS:


individual. Whether the individual is influenced
through generations of female ancestors exercised
with colors, I must for the present leave with Mr.
Darwin, Mr. Wallace, and Mr. Grant Allen to
discuss. The transmission of the defect in the
male line alone is very frequent. But there are
cases of even the reverse on record. Dr. Pliny
Earle reported, out of 61 relatives,- 32 males and
29 females, —20 cases of color-blindness, two of
these being females. Again I would recall Cunier's
case of a lady who was color-blind. Her mother
and two sisters were the same. Her brother was
free from the defect. The lady had six children,
-one son not color-blind, and five daughters
affected like herself. The oldest daughter had
four children, - two of them girls, color-blind.
The second daughter had a boy and girl, the latter
color-blind. The fourth daughter, unmarried. The
fifth left a boy myopic, but not color-blind. We
thus have the remarkable instance of color-blindness appearing only in the females of a family for
four generations. Heredity has here apparently
acted without reference to, or directly against, the
accumulated effects of generations of exercise with
colors. It is certainly a very curious fact, that, if
generations of exercise with colors is gradually
eliminating color-blindness from females, this
should not have checked its transmission through
females exclusively for four generations.
But to return again to the reports I have
received from European gentlemen: Dr. Cohn
found among 1,061 Breslau schoolgirls none colorblind. Dr. Magnus, in Breslau, found but 1 colorblind girl among 2,216.




ITS DANGERS AND ITS DETECTION.


85


Professor Holmgren reports from Sweden having
found, among 7,119 females of all ages, 19, or 0.26
per cent, color-blind.
Dr. Minder, in Berne, reports, among 846 girls
and women, having found 11 color-blind, or the
very large per cent of 1.3.
To recapitulate from a number of observers,OBSEBVB.     Country.  |   | E    V|Position of Persons
|          |3I Coun|try| Q |  Tested.
Dr. Dor.. Berlin..  611  5.82 Working-women.
Dr. Fontenoy  Copenhagen  50  0   -   ailroad employes.
Dr. Magnus   Breslau.   2,216  1.04 Schoolgirls.
Dr. Cohn.. 1,061  0  -.
Dr. Minder   Berne..  846 11 1.30    "
Prof. Holmgren, Sweden.. 3,244  9.27 School-children.
' ".. 1,374  3.21   Ad..   97  3 3.09 Confirmed.
-..  1,826  3.16  Factory-girls.
524  1.19 Railroad attendants.
51  0   - Old women.
Dr. Jefries.  Boston     7,942  4.052 Students and scholars.
My want of success in finding more color-blind
females would have at first rendered me doubtful
of my testing; but that was not the case when I
commenced with females. I have often thought
that I had found a case; but was quickly convinced, as were the bystanders, that it would not
stand the test, and was but the result of nervousness, carelessness, or stupidity. Females work so
rapidly in sorting the worsteds, that the examiner
will notice immediately the slightest hesitation or
mistake, as do also those who are waiting their
turn. The excessive ratio reported by Dr. Minder
of Berne, I cannot but think, may be due to a lack
of practical familiarity with the use of Professor
Holmgren's test with females. He admits that, in




86


COLOR-BLINDNESS:


cases he thought most perfect, the girl was subsequently proved to have been picking out only the
"most brilliant colors."  This I have seen often
enough among school girls as well as boys. As I
have elsewhere said, it is most curious how carelessness and stupidity will at first simulate colorblindness; and if we do not push on with the
test long enough, and be on our guard, we may
quite readily mark, as at least partially color-blind,
females who are really not deficient in chromatic
sense. Besides those in my records, I know of two
or three color-blind females, and of two families
who have color-blind female members. A natural
delicacy and sensitiveness render research often
difficult or impossible. In time this peculiarity
of vision will be found too common to be regarded
as a defect, much as near-sightedness now is; and
then investigations of heredity will be more easily
carried out. At present it is hardly understood
and appreciated even amongst physicians, much
less amongst the laity, though interested personally.




ITS DANGERS AND ITS DETECTION.    87
The following table gives my own results with
adults and schoolgirls:

6.o          Completely.     -
POSITION OF     0S     |           -                  |,0.              -.       a
PERSONS TESTED.. $     4
0


Female students of
Wellesley College,             Young
Mass.                -     302     n     1    -     -    1
Students of State Art.           women
School..        -      84 Adults.   -    -     -    -
Girls of the Public
Schools of Boston.
Normal...  -   123   20     -     -     -
Latin....    -     63 13 to 18  -     -     -
High....    -     796 18 to 19  -    -     -   -
Roxbury High..    -     43 14 to 18  -     -     -
Dorchester High.    -     39    "      -     -     -
Charlestown High.    -     89           -     -     -
West Roxbury High,     -     42    "      -     -     1   1
Brighton High..    -     35           -     -     -
Grammar Schools.
Bowditch Grammar.     -    341 8 to 15   -
Bowdoin Grammar.      -    398           -     -     -
Hancock Grammar.      -    486    "      -     -     -
Wells Grammar.    -    451    "      -     -     -
Exeter-st. Grammar,    -     90           -     -     -   -
Sherwin Grammar.      -    500           -     -    -
Andrew Grammar.       -    215           -     -    -
Winthrop Grammar.      -    963    "      -     -
Dearborn Grammar.     -    407    "      -     1    -    1
Comins Grammar.    -    348           -     -    -
Dillaway...    -    332           -     -    -
Shurtleff..        -    653    "      -          -
Gaston...    -    411    "      -     -     1   1
Norcross...    -     731          -     -    -


Total...  -  7,942  -   1  1  2.062
T...    - l;~i111~~




88


COLOR-BLINDNESS:


CHAPTER XI.
CONCEALMENT OF COLOR-BLINDNESS IN PRACTICAL LIFE.
SUCH statistics as I have given as to the frequency of color-blindness may, perhaps, fairly challenge criticism, and it be asked, If this is the
truth, how is it that such a chromatic defect is
generally unknown or concealed? Sir J. F. W.
'Herschel, in,1859, when commenting on Mr. Pole's
description of his own color-blindness, remarked,"I may be, perhaps, allowed to add a few words as to the
statistics of this subject. Dr. Wilson gives it as the result
of his inquiries, that one person in every eighteen is colorblind in some marked degree, and that one in fifty-five confounds red with green. Were the average any thing like
this, it seems inconceivable that the phenomenon of colorblindness should not be one of vulgar notoriety, or that it
should strike almost all uneducated persons, when told of
it, as something approaching to absurdity. Nor can I think
that in military operations (as, for instance, in the placing of
men as sentinels at outposts) the existence, on an average,
of one soldier in every fifty-five unable to distinguish a
scarlet coat from green grass, would not issue in grave inconvenience, and ere this have forced itself into prominence
by producing mischief. Among the circle of my own personal acquaintance, I have only known two, though, of




ITS DANGERS AND ITS DETECTION.


89


course, I have heard of, and been placed in correspondence
with, several; and a neighbor of mine, who takes great
delight in horticulture, and has a superb collection of exotic
flowers, informs me, that, among the multitude of persons
who have seen and admired it, he does not recollect having
met with one who appeared incapable of appreciating the
variety and richness of the tints, or insensible to the brilliancy of the numerous shades of red and scarlet. It may
be, however, that the percentage is on the increase. Certainly we hear of more cases than formerly; but this probably arises from the fact of this, like many other subjects,
being made more generally matter of conversation."
I introduce these remarks, as they very well
illustrate the general position of scientific men -
aside, of course, from physiologists -in reference
to color-blindness. This has continued pretty
much the same till within the last three years;
when methods of testing have been used, so simple,
so rapid, and so convincing, as to enable us to
gather reliable statistics on a very large scale, and
detect and expose the color-blind against their own
belief as well as that of others.
It must, however, be shown how the color-blind
have heretofore, and do now, escape detection in
the every-day walks of life. This will, at the
same time, give us a clearer idea of the peculiarities of this chromatic defect, and clear up some of
its seeming mysteries. In the first place, I must
call especial attention to the very great ignorance
of the common names of colors among the normaleyed below the well-educated class in the community, and the very general misuse of the names of
colors known or remembered.     This I have seen
to such an extent in the thousands of school-children I have tested, as to excite the wonder and
even incredulity of the teachers watching my




90


COLOR-BLINDNESS:


work. Repeatedly an instructor has wanted to
mark a boy color-blind because he so utterly
failed in designating colors, or even using their
names, when my test proved conclusively that he
had normal chromatic perception. It convinced
those interested of the great necessity of teaching
colors and their names in the primary schools, as
part of educational work. Now, the color-blind
simulate just this sort of ignorance in every-day
life, and hence are concealed, or escape detection,
through the want of education of the normal-eyed.
There is no greater subject of dispute than the
question of color. Hardly any two people will
agree as to names of certain given colors. This is
often a source of amazement and amusement to
the color-blind, who naturally think, that, if there
is such doubt as to colors and names, their own
doubts and mistakes arise from the same cause.
Many persons have been indignant with me for
marking them as deficient in color-perception, so
assured were they that they lacked only names, and
this even when a most amusing and convincing
proof of their defect was before the bystanders.
Dalton long ago spoke of this. He says, when
speaking of three of his pupils, whom he found
like himself, "They, like all the rest of us colorblind, were not aware of their actually seeing
colors different from other people, but imagined
there was great perplexity in the names ascribed
to particular colors."
Mr. Prior, in "Nature," Dec. 12, 1878, says, as
to the general inaccuracy of the names of colors,
and the unfixed character of language, "I took
to a flower-show at Taunton a dahlia of a rather




ITS DANGERS AND ITS DETECTION.


91


common variety, and such as most gardeners
would call purple, — a dark pink, with a shade
of blue over it, - and requested forty-four different people to write me down what they would call
its color. In their replies I got fourteen different
names for it. I sent a flower of the same kind to
a lady, who returned me twelve replies from members of her family and friends, and in the twelve
were eight different names." I would here refer
to the very interesting chapter on the growth of
the color vocabulary in Mr. Grant Allen's book,
"The Color-Sense."
I cannot do better than give also the statements
of another highly-educated color-blind, from whom
I have before quoted (Mr. William Pole), who
says," The color-blind must be very liable to associate, almost
indissolubly, the true normal name of a color with the
sensation it conveys to their minds, whatever that sensation
may be; and they may, therefore, easily be led to speak of
that color as if they saw it like other people, although the
sensation they refer to may be really of quite a different
nature to that which the name implies. A color-blind per-.
son will be especially loth to believe that certain colors,
which he hears about and talks about every hour of the day,
can be invisible to him. Objects of these hues will probably
present to his mind some ideas of color (though not the true
ones), and he may naturally imagine, therefore, that he does
see them, and may give his description accordingly. And
this sort of error is very much enhanced by the fact that it
is not an easy matter to refer different tones of any one color
to the same color-sensation; so that a modification of tone,
if considerable, may be easily supposed to be a different
color. I believe this difficulty is also felt by the normaleyed; and the popular nomenclature of colors furnishes
illustrations of the fact, different tones of the same color
having often different names, and being treated as separate




92


COLOR-BLINDNESS:


colors. Pink and crimson, lilac and violet, are well-acknowledged examples of this; and a dark shade of orange is called
brown, which generally passes for a separate color. Hence
we may easily see what a great probability there is that the
color-blind may acquire the habit of attaching the names of
different colors to what are, in reality, only varieties of the
same sensation; and as this habit dates from their infancy,
and is encouraged by their every-day communication with
the world, it is much more difficult to get rid of than might
be supposed. The sufferer may find himself continually
blundering; but he must go through a very rigid selfexamination before he can trace this to the fact that some
of the principal ideas he has all his life held upon color
are mere delusions. Taking red as an example, it is in the
highest degree natural that persons who are continually
seeing this color under the appearance of dark yellow
should imagine that the latter sensation (which is certainly very distinct from that of full yellow) is what corresponds to the term red; and the notion that they cannot
really see red at all is one they have the greatest difficulty
in comprehending. Hence the very general assertion by the
color-blind that they do see red,-an assertion which I
think has been far more readily accepted than it ought
to be. Red is a more common color than dark yellow; and
hence the preference, by the color-blind, of the former name
for the common sensation. A great variety of bodies are
known to be red by habit and association, and are for this
reason often named correctly. My own experience is very
decided on this point. It is only after long and careful
investigation I have come to the conclusion that my sensations of color are limited to blue and yellow. But, before I
found this out, -that is, for nearly thirty years of my life,
-I firmly believed that what I now know to be only differences in tone of one or the other of these were different
colors; and hence I was in the habit of talking of red, crimson, scarlet, green, brown, purple, pink, orange, &c.,- not, of
course, with the confidence of the normal-eyed, but still
with a full belief that I saw them. If, therefore, at that
time, any scientific man had examined me, I should have
given him a description of my case, which I now, after more
careful study, know would have been entirely wrong. I




ITS DANGERS AND ITS DETECTION.


93


should have told him, among other incorrect statements,
that I saw red objects of a full tone, such as vermilion,
soldiers' coats, &c., perfectly well; and I could, if necessary,
have supported my assertion by naming correctly a great
variety of bodies having this color, which, indeed, I am in
the habit of doing every day. It would have been inferred,
with great appearance of truth, that I was really impressible
with the red sensation; but I now see what an erroneous
inference this would have been.
"Another source of confusion in interpreting the descriptions of the color-blind is the want of due appreciation of
the different sensations that may be produced on their minds
by modified hues of the same general color. The normaleyed person considers green, for example, as always green,
whether it be yellow green, neutral green, or blue green.
Whatever the particular ' shade of green,' as it is called, it
still has, iu his eye, the distinguishing character of greenness, which cannot be hidden or disguised by any predominance of blue or yellow it may contain. But with the colorblind this identifying characteristic of greenness is wanting;
and hence several patients, speaking of green, may, by each
having reference in his own mind to some different hue of
the color, describe it in the most contradictory terms. One
may say, with perfect sincerity, that green appears to him
like red; another, that it looks yellow; a third, blue; afourth,
black; a fifth, orange; a sixth, violet, - from which the normal-eyed examiner, impressed with the unity of greenness,
may naturally infer that each person is suffering under a different species of the disorder; while, by proper interpretation, these anomalous descriptions would only convey the
expression of one consistent truth, and one perfectly uniform defect of vision."
This very clear and admirable description of a
color-blind's perception not only shows us how and
what they see, but it also explains some of the
very many ways in which they escape detection.
If so intelligent a person as Mr. Pole could have
been so long ignorant of his own perception, we
need not wonder that the uneducated color-blind




94               COLOR-BLINDNESS:
should not be aware of their defect even in adult
life, and still less that their defect remains concealed.
Let us turn now to Professor Holmgren's valuable remarks on this point. He says, -
" We must remember that color-blindness is not a disease,
in the sense of being attended with suffering, obliging the
individual to have recourse to a physician. Color-blindness,
quite as well as normal sight, is a sense of color, though of
another and a more simple nature. He whom we call colorblind is not, correctly speaking, at all blind to colors. He
perceives, in the main, the same kind of light as the normal
observer, but sees a part of it in another manner. In the
system according to which he arranges his colors, he has
fewer kinds than the normal observer; and this is why he is
obliged to classify under the same denomination a portion of
the colors classed by the normal observer under different
heads. It results from this that he finds resemblances between colors, or confuses others, that the normal observer
finds different; for instance, red and green. These confusions naturally surprise and amuse the normal observer,
who readily imagines that it arises from very great ignorance
of colors, or from defective training. He ordinarily supposes that there is no limit to the mistakes the color-blind
might make in this respect. But such is not the case: he
obeys laws quite as exact as does the normal observer. A
color-blind person can no more accustom himself to seeing
colors as the normal observer does, than the red-blind can
see colors in the same way that the green-blind does, or
conversely.
" This theory, which is based upon experience, explains
to us how the color-blind see colors; but, if we only base
our ideas on the names given to colors by the color-blind, we
can be easily deceived. To judge correctly of color-blindness, and the various practical questions connected with it, it
is of the highest importance to distinctly observe the difference between the manner in which the color-blind person sees,
and the manner in which he names, colors. The sensation is
based upon the nature of the sense of color in the organization of the optic nerve from birth. The name, on the con



ITS DANGERS AND ITS DETECTION.           95
trary, is learned. It is conventional: it depends upon
exercise and habit. The names of colors are naturally the
objective expression of subjective sensations; but, on the
other hand, they are regulated by the system of normal
sight, and cannot, consequently, agree with that of the colorblind. They can, nevertheless, be learned by the latter, and
even applied correctly in many cases. There is connected
with this fact a peculiarity of the utmost importance practically to the question in point, and one that has given rise
to the most serious embarrassments and misunderstandings.
This has been and is still one of the chief causes of our
erroneous ideas on the subject of color-blindness existing in
the masses, because it is the veil under which this defect
usually conceals itself from our observation in every-day
life, and under which, even to the last moment, it will succeed in escaping discovery in cases where, as frequently
happens, the methods of exploration employed are indecisive,
or are based upon erroneous principles.
"If we reflect on the condition of the color-blind, it is
difficult to understand how he can avoid being detected in
his daily intercourse with men endowed with normal sight.
And yet experience has sufficiently controverted this idea.
That which we have acquired in examining en masse the
personnel of a railway, for example, where it is required
night and day to give attention to colored signals, is singularly worthy of notice. We learn by it that a number of
color-blind were discovered, although their defective,sense
of color had never been suspected by themselves or any one
else, and the majority had correctly performed their duties."
Very few of us who have good color-perception
are aware how wholly the name of a color becomes
the name of an attribute of any special object, and
hence how this name may be misplaced. It seems
hardly possible that, notwithstanding a good colorperception, the names of color are so much a matter
of learning and memory. As Professor Holmgren
says, -
"This especially applies to the color-blind, who seek in
every way, and without themselves being aware of it, to




96              COLOR-BLINDNESS:
supplement the chromatic sense nature has refused them.
As color is an immutable quality of a number of objects,
some of which are of one, some of another color, it is not
very difficult to learn by heart the names of their colors.
The immediate impression is not necessary for this. We
may hear a blind person, even one born so, give the exact
names of the colors of ordinary and well-known objects of
which he has heard. For a color-blind person this is easier,
because he obtains some help from his incomplete chromatic
sense."
To practically test this, I thought of examining
some young blind people before whom the subject
had not been discussed, and who would answer to
the best of their knowledge and ability. The following table contains the results obtained in seven
such cases. The last, the eighth, a boy of fifteen,
was not wholly blind to color; and it will be seen
how different his answers were. He was practically as blind as the other seven as to form, &c.




What Color is-         Boy-14.            Boy-16.             Boy-15.               Boy-10.*


1
2
3
4
5
6
7
8
9
10
11
12


Sky?.
Grass?..
Water?
Apple?.
Cherry?
Strawberry?
Banana?
Autumn leaves?.
Spring leaves?.
Orange?
This house, Perkins
Institution?
Bricks?.


Blue.
Green.
No color; blue.
Green.
Different colors; red.
Red.
Don't know; no idea.
Green; kind of brown;
dark.
Green.
Think red.
Don't know.
Black.


Blue.
Green.
No color.
Yellow.
Red.
Don't know.
Yellow.
Different colors,-red,
blue, green.
Dark.
Yellow.
Sort of white.
Sort of light; no special.


Blue when clear.
Green.
Ocean blue near shore;
different colors.
Don't know.
Black and red.
Don't know.
Don't know.
Don't know.
Green, I believe.
Don't know; sort of
yellow.
Don't know; think
white.
Don't know.


Red.
Green.
White; no other color.
Red.
Red.
Red.
Don't know; never had one.
Green, white, blue; green at
Thanksgiving.
Answer not recorded.
Very red.


H
zH
0.1
H~
04


Think it is white, ain't it?


Black.


I                                                                                                                                                                                                                                                                            I


* Color of his hair. He laughed, and said red.




Boy- 15.
What Color is-          Boy- 13.*             Girl - 19.t          Girl - 12.              t      B-5.
Not wholly blind.


1
2
3
4
5
6
7
8
9
10
11
12


Sky?..
Grass?..
Water?
Apple?.
Cherry?
Strawberry?
Banana?
Autumn leaves?.
Spring leaves?.
Orange?
This house, Perkins
Institution?
Bricks?


Don't know.
Guess green.
Don't know.
Guess red.
Some are green.
Don't know.
Don't know.
Green, I guess.
Don't know.
Don't know.
Guess kind of red.
Don't remember.


Blue.
Green.
No color; colorless.
Red and white.
Red or black.
Red.
Green;, uncertain.
Different colors; heard
they were brown,
red, yellow.
Green.
Yellow; red.
Don't know.
Red.


Different colors.
Green.
No color; ocean is blue.
Don't know.
Some are red.
Red.
Don't know.
Don't know; don't remember.
Green.
Some are red, anyway.
Don't know.
Think they would be
sort of black.


Blue.
Green.
No color.
Different colors and shades.
Don't know; different shades.
Red.
Never noticed.
Green in summer; different
tints to brownish.
Green.
Not exactly red; orange color.


0
0
t74
0
z~


White.
Red.


~~


* He felt his coat, and said it " felt green." Pants " black," quickly answered. t Apron pink, dress green and white, as they were.
t Don't remember dress orapron; bed-spread white; boots black. ~ He can see colors but poorly; says " they are hard to get hold of."




ITS DANGERS AND ITS DETECTION.


99


These seven young people were pupils of the
Perkins Institution for the Blind at South Boston,
who were blind from birth, not only as to form,
but also as to color. The importance of this point
will perhaps only be appreciated by the specialist,
who is aware that those wholly blind as to form
may enjoy quite good color-sense. The superintendent had informed me that "there were only
eleven who were blind from birth, and about thirteen pupils who were supposed to have lost their
sight before the age of four months." I found,
however, I had to reject all but the seven from my
list. The others were, of course, practically blind;
but their knowledge of colors was to a greater or
less extent learned through the eye, and not merely
a name for a quality. Their answers to my questions were very different, as will be seen by those
of one of them, which I append to my list. He
had to look for some time at a bright-red book to
determine its color, and voluntarily said it was
"hard for him to get hold of colors." Before I
tried him with the red book, I noticed his answers
were peculiar; and he spoke of " shades of color."
I was confident that the others were totally blind,
both to color and light, from examination of their
eyes, and by testing with colored objects, and questioning as to the position of the large windows in
the room, &c. These pupils were not aware of
what was to be asked of them, and those examined
not allowed to communicate with the others waiting. They will naturally be useless for further
tests of this character, as the colors of objects will
be now pretty thoroughly talked about in the institution, and much learned from intercommunica



100


COLOR-BLINDNESS:


tion as to the " color-name " of objects, if I may
use this term. I doubt if any but a specialist, and
one wholly on his guard, could have obtained just
this interesting series of answers. Difference in
intelligence and memory was marked, and largely
decided the answers given, as also the way they
were given. The examination was extremely interesting, and the pupils seemed to be rather
pleased at being put to the test of their knowledge
and memory. The two girls answered quickly as
to water, having lately heard a lecture about it.
As to the sky and water, teaching had, of course, a
direct bearing; the very way some replies were
given proving they were learned by the ear, and
not by the eye. Could the look of the face or
gesture or tone be added to these answers here
simply written down in short, much more force
would be given my argument. Through the ear
alone these answers were learned, and retained by
memory. The attachment of the name of a color
to an object is an attribute not learned by the eye
alone. A wholly uneducated person who handles
bricks, if he hears them called black, will so call
them when questioned as to their color.
Dr. Stilling says, as a word of warning to those
who are testing for color-blindness,
' It is a well-known fact that color-blind persons, by
exercising their faculty of judgment, can aid their want of
sensibility, and are able to conceal their defect to a certain
extent. They have learned the names of colors quite as
well as normal-sighted people; and by the help of every
outward sign they have acquired a certain knowledge of
those pigments to the characteristic tints of which they are
blind. Very often that knowledge is developed in a surprising degree. Therefore, in testing one who is color-blind, we




ITS DANGERS AND ITS DETECTION.            101
must take away the possibility of employing any of those
outward characteristics which he is wont to make use of
according to long experience. This is so much the more
important, as most persons of this description have not the
least suspicion of their imperfect power of sight. Only very
intelligent people understand their defect."
Professor Holmgren very shrewdly observes, -," If we watch the development, or rather the education of
the child's color-perception, it will be seen that they first
learn the names of colors, and afterwards their correct use,
in defining characteristic peculiarities of known objects. It
is much later that they notice the quality of the light in
correctly designating colored objects they have not previously seen. The child with defective color-perception
differs from the normal-eyed only in not being able to reach
this degree. He learns, like the others, that the sky is
blue, the grass green, bricks are red. He learns that the
corn is green in spring and yellow in autumn; that the poppies have a green bud, but red flowers, &c.: these and many
other things are retained in his memory. If he thinks over
the meaning of these names, he soon meets with difficulties
which may lead to very various results. Upon the colorblind eye the brick, the tile, the barley in spring and in the
fall, and the poppy-flower produce the same color-sensation,
and he can with difficulty comprehend why different names
are given to these colors. Most persons do not reflect so far,
and, regarding the problem as one they cannot solve, lose
therefore all interest in the study of colors; concerning themselves with them only when forced to. This readily explains
why the color-blind grow up without others detecting their
defective chromatic sense.  This is generally the case with
the lower classes, and especially in the country. The majority get into no difficulty from their intercourse with colors;
and, if they make gross mistakes, this is attributed to lack
of practice, or carelessness. Hence nothing more is thought
of it.
" Other persons, however, reflect further. In seekingwhy
there are two separate names for similar colors, as the grass
and bricks, they look for some more delicate mark of difference, and finally find it; but this is only the varying degree




102


COLOR-BLINDNESS:


of the intensity of the light. One color is, perhaps, paler
than the other. From the time this is noticed, they become
very timid in discriminating colors. They accustom themselves to find a difference of color in the difference of the
intensity of light, the luminosity, and lead others as well as
themselves into the error of supposing that they see the external world like other people, and that their uncertainty is
wholly due to want of practice. We find, in fact, in the
color-blind a very practised and sharp eye for variations of
intensity of light. They often have acute vision, and can
see well at a distance. The first color-blind known to science, Harris, observed this of himself; and it has been supported by nearly all observers since. There are, moreover,
very few color-blind so interested as Dalton to study their
own case, and detect their fault."
As we have seen, Mr. Pole is the only one since
Dalton's time who has studied and reported his
own chromatic defect.
I have now shown how the color-blind deceive
themselves and others, and, growing up in ignorance of their defect, escape detection. To this
must be added the very important fact, that, till
very recently, methods of testing for color-blindness have been used which were wholly inadequate to expose particularly the lighter forms of
the trouble. It must be remembered that red or
green or violet blindness may exist in any degree
from the most complete to almost normal vision.
Formerly, if a color-blind gave the right colornames to objects, he was regarded as normal-eyed;
and this has been continued notwithstanding the
repeated warnings of Seebeck, Helmholtz, Holmgren, and others. Thus many have escaped detection; whilst, on the other hand, the normal-eyed's
ignorance of names has been set down to colorblindness, giving us, as in France, most extraordinary percentage.




ITS DANGERS AND ITS DETECTION.      103
But we now know that about one male in five
and twenty is color-blind. It is impossible for all
to have grown up ignorant of their defect. How,
therefore, has this class, who are aware of their
color-blindness, escaped detection in every-day life?
The color-blind, who are quick-witted enough to
discover early that something is wrong with their
vision by the smiles of their listeners when they
mention this or that object by color, are equally
quick-witted in avoiding so doing. They have
found that there are names of certain attributes
they cannot comprehend, and hence must let alone.
They learn, also, what we forget, that so many
objects of every-day life always have the same
color, as red tiles or bricks, and the color-names of
these they use with freedom; whilst they often,
even unconsciously, are cautious not to name the
color of a new object till they have heard it applied, after which it is a mere matter of memory
stimulated by a consciousness of defect. I have
often recalled to the color-blind their own acts and
words, and surprised them by an exposure of the
mental jugglery they employed to escape detection, of which they were almost unaware, so much
had it become a matter of habit. Another important point is, that, as violet-blindness is very rare,
the vast majority of defective are red or green
blind. These persons see violet and yellow as the
normal-eyed, and they naturally apply these colornames correctly. When, therefore, they fail in red
or green, a casual observer attributes it to simple
carelessness, - hence a very ready avoidance of
detection. It does not seem possible that any one
who sees so much correctly, and whose ideas of




104


COLOR-BLINDNESS:


color so correspond with our own, cannot be
equally correct throughout, if they will but take
the pains to notice and learn. Color-blindness is
also a constant source of petty mortification, which
teaches its possessor to be on constant guard over
himself in avoiding exposure and its accompanying irritation. The intelligent color-blind finds
many ways of drawing a decision of color from
those he is in contact with, and always lets shopkeepers pick out the colors lie calls for, just as the
color-blind shopkeeper lets his customer do the
same if he can; and when he fails in this, and
makes mistakes enough to lose his place, he can
take refuge in the mourning stores, where his
defect is an advantage.
This brings us again to their extraordinary appreciation of light and shade. They can sort and
place in correct order a series of shades of red or
green much better and more quickly than the
normal-eyed, because to them the color is but so
much light and dark. Now, an educated colorblind is asked by a lady friend to buy a skein of
red worsted to match the pattern. He asks the
attendant in the store for red worsteds, and selects the one which corresponds in luminosity with
his pattern. Such good "shopping" forbids the
idea of any chromatic defect. But the worsted
attendant is away, and another, who is color-blind,
quietly hands over the greens to the purchaser:
the latter will then complacently select the one
which matches in luminosity his red pattern. If
he is green-blind, he will select a lighter green
if red-blind, a darker -than his pattern. In either
case his defect is exposed; and, in fact, it thus
often happens.




ITS DANGERS AND ITS DETECTION.           105
This sensitiveness to light and shade has enabled
color-blind painters to follow their profession with
success, and even avoid discovery, until accident or
design has interchanged, for instance, their reds
and greens. A color-blind engraver has an advantage over his fellow-workmen. It seems hardly
possible that a color-blind person should have the
ideas and thoughts, and power of expressing these,
which are derived wholly from the perception of,
and acquaintance with, colors. Hence I quote the
following as a peculiar instance of concealment of
color-blindness, where it would seem that it must
show itself.  Of a member of a well-known colorblind family, the reporter says, —
" Another of the gentlemen whose case of defective perception of colors is herein noticed, is generally acknowledged
as one of the first and greatest of American poets now living. He also is unable to distinguish one tune from another;
yet his poetry is not deficient in the requisites of perfect cadence, harmony, and rhythm. In regard to color, his defect
is such as is described in the ' worst degree' of the arrangement of Dr. Hays. He says, that, previous to the time at
which he ascertained this peculiarity of vision, he always
wondered that people should talk of 'glorious sunsets' and
'beautiful sunsets,' inasmuch as he could detect neither
' glory' nor ' beauty' in them. The kaleidoscope of nature
and the harmonicon of art are the Utopias of his mind.
The magic hues developed by the prism, the iridescence of
shells and minerals, the inimitable colors of the beasts and
birds of tropical climates, the verdure of the fields of spring,
the splendor of the autumnal foliage of the forests, the
myriad hues of flowers, and the realm of beauty which
springs, as sprang Minerva from the brain of Jupiter, from
the genius of the artist, - all these, it would appear, are,
comparatively, 'as a sealed book' to him. Yetfrom his writings no evidence of this can be detected. The poet throws his
gossamer veil of ideality before the vision of the man, converting a sombre world into a paradise like that of the Per



106


COLOR-BLINDNESS:


sian. Seated on the borders of Helicon, he looks abroad
upon a universe transformed by imagination and glowing
with all the colors of a phantasmagoria. The iris of heaven
lifts its expansive arch in hues as varied and as vivid as
when first placed there 'to establish a covenant' between
God and man; the sun descends, now invested with the
mellow tints of the skies of Italy, and now surrounded by
clouds emblazoned like those which attend its setting in
America alone; fields are clad with a carpet of emerald,
and flowers blossom with all the diversity of coloring that
ever decked them in the gardens of the East; birds spread
to the wind pinions as gorgeous as those that wave over the
Amazon or the Ganges; and the mineral world glitters with
the concentrated beauty of amethyst, topaz, beryl, and all
the precious stones adorning the foundations of the wall
of the New Jerusalem which was revealed unto the apostle
at Patmos."
As the color of most of our common berries and
fruits, when ripe, is the complementary of that of
the green foliage, the inability to see and collect
them is a very frequent source of the exposure of
the color-blind both to themselves and their surroundings in early life. It is therefore a wonder
how a person can grow up, and not be found out,
much less not find themselves out.
Professor Wilson, in his book, says of a chemist
aged twenty-eight, green-blind, -
" He worked five months in my laboratory; and some
time elapsed before I discovered his color-blindness, which
he was not ready to acknowledge, and could to a great extent conceal by his sagacity in observing those properties
of bodies which are not affected by color. He unconsciously
betrayed an effort to supplement his defective vision of
colors by all secondary aids. If colored papers were shown
him, he fixed upon any difference in shape, smoothness, or
configuration which they presented, and, when they were
shown him again, recognized them by differences which
would have escaped most other eyes. He would frequently,




ITS DANGERS AND ITS DETECTION.          107
accordingly, have appeared to a stranger to recognize colors,
when in reality he was only recalling form, or condition of
surface, of the colored body."
I was lately called upon to test some employds
in a large printing-house, and found two, among
the seventeen presented to me, color-blind. The
astonishment of their fellow-workmen was very
great; and they would not believe one of the men
could be defective, since his employment was cutting up colored cardboard and paper. They carried him to his post, and asked him to pick out
the colors, which he did, as they were always kept
in certain positions on the shelves. The members
of the firm, however, were convinced by the examination, and quickly realized the risk of loss of
material and time from the man's defect, hitherto
unsuspected.
An interesting instance of what constant practice will do in helping a color-blind to avoid mistake and detection is given by Dr. Minder, who
says, -
"1 On this point (of possible alleviation or cure) a description of three cases of color-blindness in a Jewish family of
Berne will be of value. They are brothers, the youngest
already over fifty years of age. They are all feebly redblind, and happen to be in business which requires daily
intercourse with colors. They all make the same mistakes
when tested with the worked-worsted tables. I could unfortunately only persuade one to be more thoroughly tested.
To my surprise I only detected him by Holmgren's test
after repeated trials, and that by his matching bright-blue
and rose color. I-le is a very intelligent gentleman, whose
business has required him for more than thirty years to be
daily busied with colors, with which, according to his own
and his wife's report, he formerly made constant mistakes.
These have, in the course of years, occurred less and less




108


COLOR-BLINDNESS:


frequently. He was even very highly valued for his fine
appreciation of colors, and taste in their selection, by a Paris
ribbon-factory with which he was connected. He attends
alone to all the buying for, his large business, and is only
liable to mistake with dark green and black, rose and light
blue. According to his statement, he could not, in early
years, be certain of violet and green. I was perfectly
astonished at his power of distinguishing the various colors,
and the number of names he had at disposal for the finest
shades. I was equally surprised at his so accurate comparison of the several colors with each other. To this he
attributed his so greatly cultivated color-perception. He
laughed, therefore, at Holmgren's method of comparison,
by which he was, he thought, not to be caught; and, in fact,
this could only be done with difficulty. The results of
other methods were negative, except with the polariscope,
where he always stopped at rose and bright blue, which, he
declared, were alike, and sometimes called them both rose,
and sometimes bright blue."
This case led Dr. Minder - as it would also
likely lead others- to suppose that there was a
basis for Dr. Favre's belief in the curability of
color-blindness by exercise and practice with colors; but no one can have tested and talked with
many color-blind without being convinced that we
can hardly set any limit to their capacity for learning other attributes of colored objects, and recognizing and remembering their color-names through
this alone. Thus, as we now well know, they
may even deceive themselves, as well as others,
into the belief that they have gained by practice
a color-perception they were not born with. This
we shall see in Professor Delbceuf's supposed correction of color-blindness by looking through certain transparent media.
A brother-practitioner, who is color-blind, and
whom I was testing by Holmgren's method, after




ITS DANGERS AND ITS DETECTION.         109
sitting some time with the one hundred and fifty
little skeins of worsted before him, finally said, " I
have tried so hard to supplement my defect by
every possible means, and catch other attributes
than color to recall the names of them, that, if you
will give me two or three days to study over these
worsteds, and tell me what their colors are, I will
afterwards pick them all out correctly; but I shall
see them no differently."
My friend, Dr. Henry Power, writes me from
London, June 1, 1878,"Color-blindness is a subject of great public concern.
As showing also its private relation, I may mention an
interesting case that came under my care lately, in which
the man was a draper, who had long, by great ingenuity,
conducted a business on his own account; always getting
an assistant to bring down the particular bundle of color
demanded by the customer, and then selecting the particular tint by its shade. He was now going into a much larger
business, and wanted to know if his disease could be cured,
or whether his future partners should be told of his defect.
A " no " and a "1 yes " settled these points, and I have heard
no more of him; but it was curious, that, in the course of
twenty-five years, he had never been found out."
I was recently told of the following: Some five
and twenty years ago, before color-blindness was
so well known or talked of, a student of the Royal
Academy in London -who was selected, not only
by the authorities, but also by his fellow-students,
as having about the best perception for form, and
power of light and shade - turned to the use of
colors. In this it was naturally supposed he would
exhibit extraordinary talent, and become a great
painter. He was allowed to take a portrait by
Titian from the National Gallery, and have it in a
small room to himself. There he copied it to his




110           COLOR-BLINDNESS:
best ability, as he stated to the principal and his
brother-students. No one had seen him at work.
His result was the most perfect copy as far as
light and shade went, but in pea-green. He finally
became an engraver.




ITS DANGERS AND ITS DETECTION.


ill


CHAPTER XII.
INCURABILITY OF CONGENITAL COLOR-BLINDNESS.
Tim question of the curability of congenital
color-blindness is one of considerable importance;
for certainly the color-blind railroad employ6 or
pilot should not be dismissed from service if he
can be cured of his defect.
It has been till lately universally admitted by
ophthalmic surgeons and physiologists that congenital color-blindness was incurable by any known
means. In August, 1874, Dr. A. Favre of Lyons,
France, reported to the French Congress for the
Advancement of Science, at Lille, some observations, which seemed to him to prove that congenital
color-blindness was curable both in children and
adults by exercising the chromatic sense. Dr.
Favre has for the last twenty years or more, as
consulting surgeon of the Paris, Lyons, and Mediterranean Railroad Company, pressed the necessity
of examining all railroad employds for color-blindness, led so to do principally by the results of
Wilson and Potton. He has succeeded in inducing other roads to adopt similar precautions, and
deserves great credit for his exertions.  It is




112


COLOR-BLINDNESS:


therefore due him to look carefully at his statements, as, if correct, they are of the utmost importance.
He reports the results in eleven different schools
of the examination of 1,002 boys between the
ages of four and fifteen. These their teachers
tested by asking them to name the color of objects
exhibited of five principal colors. The teachers
reported to Dr. Favre that they found at least
218 defective in chromatic sense, and that almost
all were perfectly cured by being repeatedly shown
objects, and told the names of their colors till they
were learned. Amongst 138 girls, from seven to
fourteen years of age, Dr. Favre himself found
only 2 whom he regarded as color-blind. These
girls, he remarks, were under excellent teachers,
and a large number had passed through the salles
d'asile, where colors were taught. Dr. Favre then
says, -
"The examination of these several reports shows that
many children of both sexes come into the salles d'asile and
schools without a notion of the elementary colors. The
number of children lacking in this sensation in the majority
of boys' schools I have visited is from twenty to thirty per
cent. This ratio diminishes in proportion as the attention
of the scholars is directed by their teachers to colored objects. Certain exercises, the painting of plans, geographical
cards, lessons in natural history, &c., have an evident influence on the scholars' progress in this sense. Amongst the
girls, sewing-work, embroidery, the care of the clothing,
the handling of flowers, much reduces at eight years of age the
number of those who have difficulty in distinguishing one or
more of the elementary colors. At this age the number of
boys who make marked mistakes in naming colors is still
quite large; and we have found, that, if the majority easily
acquire a knowledge of colors, many of these need watchful
and continued care, requiring to be examined periodically,




ITS DANGERS AND ITS DETECTION.          113
so to speak, till we are assured of their cure. What is the
best method to use in the schools? Experience may teach
us further; but, from our observations during the last five
years, we feel authorized to draw the following conclusions:
Male and female teachers should be required - (1) To question separately the scholars of their class as to the five elementary colors, and also as to white and black. (2) To
carefully record, at the time of examination, the scholar's
replies against his name.  (3) The scholars who have
made mistakes should be individually called twice a week,
and the colors named before them; they should be questioned and taught till it is shown that they have acquired an
exact notion of the elementary colors. (4) There should
be periodic examinations.  (5) Whenever occasion presents, the precise names of colored objects exhibited should
be spoken before the whole class. (6) An advanced course
on colors should be given scholars destined for special professions, by the aid of Chevreul's color-chart and the most
commonly manufactured articles.
" The treatment of color-blindness in the adult also has
given us very conclusive results, which we have embraced
in an unpublished article presented to the Academy of Science. "
Dr. Favre says again elsewhere,
" I call for the introduction of exercises with colors in all
the schools, in the army, in the marine, and on the railroads.
I am persuaded, that, by the precautions I have indicated, a
great number of accidents may be avoided; and I hope to
be so fortunate as to cause congenital Daltonism to be
stricken from the nosological list."
Dr. Favre has here undoubtedly simply mistaken
the lack of knowledge of the name of a color for
a lack of perception of the color. In this mistake
he has been confirmed by the rather extraordinary reports from his several friends who were
teachers. These latter, I must at once insist, were
wholly incompetent to decide whether their scholars were color-blind. We must of course first




114


COLOR-BLINDNESS:


positively prove the existence of the defect before
we can talk about having cured it. It is next to
impossible for even an expert to decide whether a
child is color-blind by simply asking him to name
the color of pieces of paper or other objects. It
is, on the other hand, very possible to teach him
a name which he shall attach to the object, as it
would also be to teach a congenital blind person.
These children, supposed color-blind, are reported
as cured by more or less exercise with colors,
according to their individual quickness and memory in catching and retaining their names. Those
that were dull, inattentive, and forgetful, required
repeated exercises before they retained the names
of colors which were seemingly readily forgotten.
This is perfectly shown by the teachers' reports.
The reported percentage of defective color-perception found would of itself throw much doubt
on the method of testing. For instance, as many
as thirty out of fifty, and fifteen out of thirty-five,
children are reported having " no notion of color."
But ten per cent is a very large ratio, even when
we include all cases of only slight color-blindness.
Now, these children were from four to fifteen years
of age. How many schoolboys at this time of life
know the names of five colors, or, having heard
them, will apply them correctly when questioned,
without being specially taught?
We have found it very different with girls, as
did Dr. Favre. They use the names of colors
much more frequently, and have more to do with
colored objects in dress, trimmings, &c.
Those of us who possess normal color-perception
know how difficult it is to tell the difference




ITS DANGERS AND ITS DETECTION.         115
between light greens and blues. This formed a
large class among these supposed defective children, and they were reported cured in four or five
exercises.  A  further convincing proof of the
inadequacy of the test employed, and of the disqualification of the teachers as examiners, is shown
by their reporting children as confounding those
colors which the color-blind never do; for example, red and violet. I would not, of course, deny
that amongst these thousand children there were
any color-blind. Proof to the contrary exists in
the statement of one teacher, who says, "I sometimes despaired of curing one child, six and a half
years old, who, after sixty-five exercises, could not
tell me a single color without hesitation. Eleven
exercises more, however, cured this unexampled
Daltonian, who began by first distinguishing green,
and finished by not always calling red yellow
when shown him." This child, no doubt, was colorblind, and took this length of time to learn the
name of a color to be repeated whenever the same
object was shown him. If alive, I am certain this
boy is as color-blind now as then; and any test
not calling for the use of names would undoubtedly prove it. Professor Helmholtz, in his " Physiological Optics " (p. 299, 1867), said, -
" As to the examination of the color-blind, simply asking
them to name this or that color, will naturally elicit but very
little, since they are then forced to apply the system of
names adapted to normal perception to their own perception, for which it is not adapted. It is not only not adapted,
because it contains too many names, but, in the series of
spectral colors, we designate differences of tone as such, which
to the color-blind are only variations of saturation or luminosity. It is more than doubtful whether what they call
yellow and blue correspond to our yellow and blue."




116


COLOR-BLINDNESS:


At first sight it seems only natural that we
should be able to improve our color-perception by
use, as we may sharpen our other senses by exercise; but in the color-blind there is a congenital
defect or deficiency. With the ear we may learn
to distinguish sounds whose vibrations come within
the range of our scale; but no amount of instruction can make us hear a note above or below the
vibratory scale of our ear. A little practice will
enable the normal eye to discriminate between the
lighter shades of green and blue, which at first it
had confounded; but no amount of exercise with
colors can cause the color-blind eye to perceive
those colors as we do, to whose ethereal wave
lengths or numbers it is not adapted. However
much practice may cultivate the power of an
organ, it can never give that organ a different or
additional power. I admit that constant exercise
may enable a person only partially color-blind to
improve his capacity for discriminating colors; but
even then I do not believe he has altered his colorperception, but only supplemented it by additional
means, as we so often see other senses, when deficient, supplemented. Whether we shall ever be
able to cure color-blindness is another question I
am not in position to decide. I desire here only
to state my belief, shared in at present by all
physiologists and ophthalmic surgeons, that it has
not been and cannot be cured by exercise with
colors. From Dr. Favre's valuable researches, and
his well-known and recognized connection with
the present great advance in the testing for colorblindness amongst railroad employ4s and elsewhere, his belief in the curability of this defect




ITS DANGERS AND ITS DETECTION.           117
might have undue weight. It must be remembered that he stands almost alone in this. I have
therefore endeavored to show how and why he
was mistaken, as others also might well be. To
this opinion I must still hold, notwithstanding Dr.
Favre's more recent article before the Lyons Medical Society, and the supposed cases of congenital
color-blindness he there describes.
I should, perhaps, not dwell on this point further,
were it not that Dr. Favre's mistake might lead to
dangerous consequences by quieting the fears of
those whose attention had been roused to the ne
cessity of testing for color-blindness. I therefore
quote from one or two authorities in support of my
opinion, to show that not only is it incurable,
so far as we yet know, but that it does not change
with time. A congenital color-blind person dies
so. Professor Wilson says, -
"Congenital color-blindness is certainly incurable, and,
when induced by injury or disease, it may become as irremediable as if it had been an inherited peculiarity; but certain
forms of this affection from disease or injury are transitory,
and admit of cure. So far as I can ascertain, from the examination of the cases of congenital color-blindness within
my reach, the amount of modification in the perception of
colors, induced by age, is inappreciable, even though no
allowance be made for that alteration in all the powers of
vision which time produces on every eye. Thus Dalton
was certainly as color-blind at the Oxford meeting of the
British Association in 1832, when he compared the color
of his D.C.L. gown to that of the leaves of trees, as in
1792, when he first discovered his color-blindness; nor did
any change, so far as his associates were aware, occur in his
perceptions of color up to his death in 1844. Mr. Milne, of
Edinburgh, is still (October, 1854) as color-blind as he
was when Mr. Combe described his case thirty years ago,
and as he had been for years before his case was described.




118             'COLOR-BLINDNESS:
Professor N. was examined as to his perception of color,
some thirty years since, by Sir David Brewster, who has
recorded his case.  He writes me recently, 'I am under
the impression that some change in appreciating colors took
place in my eye between childhood and youth. As a child,
red gooseberries seemed to me altogether blue, so far as I
remember. Latterly I have observed what I fancy red in
this variety of fruit.' And again: 'I suppose sometimes
that I can distinguish red in some objects; but probably this
is from knowing that they are usually of this color.' But
he adds, ' At any rate, I am quite sure I should make a
dangerous railway-signal man, as I most certainly would
not know a red flag from a green one.' This gentleman
further states, in answer to some queries, that pink still
appears to him by daylight blue, and by gaslight green, and
that he continues to confound carmine red by daylight with
blue. There plainly has been nothing deserving the name
of improvement in his case. Lastly, the Countess of D.
has not (in 1853) appreciably altered in her color-blindness
since her peculiarities were described by Wollaston many
years ago.
" Dr. K., a medical man, says, ' When a boy at school,
my attention was directed to my want of knowledge of color
by finding I could not see what my father called the brightred berries of the holly. When other children easily found
out the trees which were loaded with ripe cherries, I never
could, till I came so near the tree as to detect the form of
the fruit. The discovery of this defect in vision distressed
my father exceedingly; and he endeavored to cultivate in me
a knowledge of color by giving me lessons in painting,
making colored charts for me of the prismatic and other
colors, wishing to believe that the defect resulted from want
of education in color, not from a visual defect. I destroyed
many a painting of flowers, &c., by putting on wrong colors,
- as blues for purples, green for some kinds of red, and
yellow for others. I still remember the surprise he exhibited
when he found I could not detect a red cloak spread over a
hedge across a narrow field. Hedge and cloak appeared to
me the same exact hue, and they do so to this day.'
'" Dr. T., aged twenty-seven, early became aware of his
inability to distinguish colors, and has cultivated paint



ITS DANGERS AND ITS DETECTION.           119
ing in the hope of curing or diminishing his defect, but
without any success. He has himself favored me with an
account of his case; but, as he very strongly realizes the
want of a common language between himself and those who
have not his defect in distinguishing colors, he regards this
account as hopelessly imperfect.
" It is quite certain that dyers, painters, weavers, clothiers,
and the members of other callings much conversant with
color, are not unfrequently color-blind. I myself have very
recently been offered any ' reasonable fee' if I would cure a
worthy working tailor of almost total inability to distinguish
colors.
" These cases may suffice to illustrate the permanency of
this affection of vision; but they are not singular. Among
my color-blind acquaintances there are probably none who
would not sacrifice a great deal to see perfectly, and nearly
all have endeavored to cure themselves of their visual
idiosyncrasy; but not one reports a cure, and the best educated and most observant among them are the most decided
in declaring that they have given up all hopes of amendment.
" It is difficult to convince many that this conclusion is a
just one. Those whose own sense of color is delicate, and
who are led by taste or profession to live much among colored
objects, are slow to believe that any eye can be so peculiar
in its endowments as to make the blunders which the colorblind do, even in reference to what they call a 'staring' red
or green. Such colorists insist that carelessness, indifference,
or improper education lies at the bottom of the mistakes
which the supposed' color-blind make, and profess themselves willing to undertake their cure, of which, however,
they record no case.
"When we find an engraver, who for the greater part of
his life has been gazing all day at paintings, purchasing a
red window-curtain for a green one; a tailor, whose eye has
been for hours daily fixed on cloths of very varied colors,
matching green tape with scarlet linen, at the risk of losing
his situation; an experienced field-geologist compelled, when
surveying a red-sandstone district, to take a companion with
him to point out where grass ends and sandstone begins;
and a teacher of chemistry evading as much as possible




120


COLOR-BLINDNESS:


the questions of his pupils concerning the colors of bodies,
- we cannot doubt, that, after education has done all that
it can towards developing the sense of color in the colorblind, they remain as helplessly prone to make their characteristic blunders as before. A crowning example of this has
recently presented itself to me. In the establishment of a
painter and glass-stainer, who is an obstinate disbeliever in
the existence of color-blindness, my attention was recently
directed by his fellow-workmen to a youth who bad been
set to repaint the devices on the shafts of a sheaf of arrows.
These devices, consisting of alternate circles of red and green,
had not been effaced, but only dulled; yet the painter executed his task by painting all the red rings green, and all
the green rings red. The case was remarkable for the direct
reversal of the colors in question, and this by one who held
them before him to compare, both on his palette and on the
arrows. Yet the party who committed the mistake was an
excellent draughtsman, much esteemed by his master, and
surrounded at his daily work with splendid specimens of
stained glass. This mistake which he made soon ceased to
be a solitary one: for his fellow-workmen, having, since its
occurrence, put him-to the test, found him uncertain in his
judgment of many colors; and, on examining him, I found
him commit the characteristic errors of the color-blind.
Here, then, was the possessor of an educated color-blind eye
making such mistakes as no normal-eyed person, however
uneducated his power of vision might be, could or would
make. Education, then, can do nothing towards curing
congenital color-blindness; nor, in truth, can any thing else."
Dr. Goubert, in 1867, says, as to treatment of
color-blindness,
" I have here no more consoling words or fruitful resources
to present. Whatever the symptoms characterizing this
peculiar imperfection, it belongs to that large number which
the divine art of ZEsculapius is powerless to cure, perhaps
even to mitigate. All ophthalmic surgeons are unanimous
on this point."
Professor Holmgren has very thoroughly discussed Dr. Favre's publications; and he is in




ITS DANGERS AND ITS DETECTION.          121
position, both theoretically and practically, to test
attempts to cure color-blindness by exercise with
colors, &c. After citing from    his pamphlets, he
says,
"We, on our part, have not yet seen the result of a systematic exercise in learning colors pursued months or years;
but the observations we have made on the exercise of the
color-blind and their general effects may not be without
interest, and throw some light on the importance of such
exercise. We have said that the color-blind railroad employes learn to distinguish the flag-signals in common use,
and rarely make a mistake when examined, especially on this
point. Does this result depend on the training, and in what
way? The color-blind who are not railroad employds can
answer this. If we show them the ordinary flags (green and
red), one after the other, they will nearly always name one
or the other wrongly, and often both, and even sometimes
frankly admit they do not know the true names of the colors.
But if we show them the two flags at the same time, and ask
which is green and which red, they at once see a difference;
and, having fixed the name in their memory, they no longer
make mistakes, but will tell the true name of the colors, even
when shown one flag after the other. From this we see how
the color-blind railroad employe has learned to distinguish
the flags.
" But, after all, what have they learned? and what, strictly
speaking, have they gained by such recognitions? If we ask
a color-blind person who is intelligent and honest, and who
has no interest in concealing' his fault, he will openly
admit that he has no idea of the color itself, but that he
notices a sensible difference in that the green flag is darker
to his eye than the red. At the next trial he will make the
same mistake if the first flag is shown him alone, and will
be as surely correct if the two are shown together. A railroad employe who daily sees the two flags will not in general
make this mistake when the test is repeated: we readily
understand why. The color-blind has learned to apply the
names, guiding himself by the difference in the intensity of
the light; but he still continues destitute of any idea of color.
He is always color-blind, and has simply learned an artifice."




122              COLOR-BLINDNESS:
"Dr. Favre's plan of gradual exercising depends, of
course, on the same idea; only that he uses several shades
of the same color. Hence the intensity of the light is not
necessarily the distinguishing mark. The fact that in his
proposed exercises the objects are looked at close to, assists
in no small degree their being distinguished; for, close to,
there are other attributes besides color and intensity of light
observable, whilst the flags are always at a much greater
distance. The coloring material of the different wools may
present peculiarities, which we do not generally notice,
because the color itself is enough for us, but which are of
great assistance to the color-blind. What these differences
are is not readily determined. The wools, for instance, may
be smooth, rough, soft, or shining,- all qualities appealing
to the eye.
" The history of science tells us of cases of persons completely blind who could easily and correctly distinguish wool
of different colors by means of other senses, - smell, taste,
or touch. The power of touch in this case deserves especial
attention, as it is of importance in distinguishing the peculiarities of the wools above mentioned. The close connection between touch and sight in determining whether an
object is smooth, rough, &c., is well known. The assistance
which these two senses render each other in a general appreciation of every material surface is not less well known.
These are the very qualities, beyond any doubt, that the
color-blind call to their aid to supply the place of their defective color-sense. Therefore many color-blind place the
samples of wool in different lights, bring them quite close to
the eye and in different angles to the visual axis. But
many color-blind, who knew the difference between red and
green, or purple and green, frankly acknowledged that they
only recognized them because one wool was coarser, harsher,
or rougher than the other. Consequently it was not the
color, - that is, the quality of the reflected light, - but the
coloring matter and its peculiar effects upon the wool, which
were to them the distinguishing features. The color-blind
may, however, be assisted by still other more accidental
peculiarities; for instance, they may notice whether one
bunch of worsted is larger or thicker than the other. The
results of such exercise will be as useless as a lesson simply




ITS DANGERS AND ITS DETECTION.       123
learned by heart. The scholar may repeat a whole page of
his book word for word, and yet have no idea of the meaning of the contents."
As to the necessity and value of teaching the
names of colors in the schools, I entirely agree
with Dr. Favre. No better proof of it can be
given than the reports of his teacher-friends, who
found twenty to thirty per cent of their pupils
who did not know the names of colors, or could
not apply them. Such recreations as color-teaching would be interesting and valuable, since most
probably all marked cases of color-blindness would
be detected, and a scholar thus be warned in time
not to attempt work in after-life for which his
defect unfits him, of which he cannot be cured by
any now known means.
Something in the way of teaching the names of
colors has been already commenced in our Boston
schools. I have shown those interested how necessary some instruction is in colors, as also how
useless it would be to attempt to correct colorblindness by teaching names, which would only be
associated with objects, and not placed as the expression of an attribute recognized by the eye.
But the teachers must first be taught what colorblindness is, and how frequent it is, in order not to
set down as stupid, or punish, an unfortunate boy,
who seemingly will not learn colors he cannot see.
As to the possible mitigation or cure of colorblindness, my own experience with educated colorblind adults has been very interesting. All had
attempted, in one way or another, to overcome
their defect by practice, but in vain. Those who
best understood their trouble most realized this,




124


COLOR-BLINDNESS:


and eagerly asked for relief, which can be but partially obtained.
I think the necessity of discussing, as far as I
have, what at first sight seemed perhaps only a
medical opinion, has now been made apparent.
The very mistake Dr. Favre has been led into
has also deceived railroad officials, who here and
there have tested an employs, suspected of colorblindness, with the flags or lanterns used on their
individual roads. It requires considerable argument and positive proof to convince a railroad
superintendent that one of his men, whom he has
had cause to suspect, and has seemingly thoroughly
tested, is, after all, color-blind. It is very difficult
for him not to believe his employ6 has learned, or
can be made to learn, to see colors as they appear
to a normal eye. He, however, will be convinced against his reason, when the color-blind
man is in his presence subjected to a proper scientific test, applied by a competent specialist.




ITS DANGERS AND ITS DETECTION.


125


CHAPTER XIII.
PALTIATION OF CONGENITAL COLOR-BLNDNESS.
As congenital color-blindness cannot be cured
by any at present known means, the question of
its possible palliation becomes somewhat important. Many methods have naturally been suggested and tried, and of these I will now speak.
Wilson says, -
"A means of guarding against mistakes, relative to
colors, which is unquestionably of some service to the colorblind, is the reference of doubtful hues to a chromatic
scale, accurately tinted and named. But this means of correcting error soon finds its limit, as the mismatchings of red
with green, olive with brown, and purple with blue, characteristically made by the color-blind (although both colors
are presented to the eye together), are sufficient to show.
Moreover, we must remember, that-, to the color-blind, his
defective color perfectly corresponds with gray, or white
and black, as readily shown by experiment with Chevreul's
'gammes chromatiques,' or with the worsted test. Hence, by
comparison alone, he might decide that his scarlet or green
cloth is a neutral tint or gray."
Szokalski and Seebeck, as Wilson also remarks,
recommended, as a means of ameliorating the condition of the color-blind, their steady gazing, first
on a colored surface, and then on a white or black




126


COLOR-BLINDNESS:


one; but, for reasons already given, this proposal
seems of no value, nor is any proof offered that it
has been of service.
There nevertheless exists, says Wartman, a
very easy means of rectifying, to a certain extent,
the error of the appellation of color. This means
consists in examining colored objects through a
transparent medium - as a glass or a liquid - of
a certain known tint. Suppose this tint red: the
impression of a green body and of a red body, the
same at first to the naked eye, will become manifestly distinguished by the use of the transparent
screen. This method appears to have been practised for the first time by Professor Seebeck (the
father) towards the year 1817. Their employment,
however, only remedies mistakes in the specific
nature of colors, and leaves in general those which
apply to one and the same tint. Wilson says that
Dr. Steebach carried out this proposal the length
of recommending the use of colored spectacles.
Trinchinetti advises that the glasses should be of
the color which is the complement of that liable
to be seen falsely. To this Wartman justly
objects, because "the color-blind do not judge
correctly of complementary colors;" but his own
proposal to employ transparent media of other
colors is liable to as great objections. Wilson
adds, -
"I am far from wishing to affirm that a color-blind person may not be aided in correcting his chromatic errors by
such a use of colored glasses as Seebeck and Wartman
recommend; but, after many trials with my color-blind
acquaintances, I have found none who could turn the suggestion to practical account. My trials have been chiefly
made upon those who confused red with green, to whom




ITS DANGERS AND ITS DETECTION.           127
Wartman, in illustrating the use of colored transparent
media, specially refers; but I have met with no success."
In 1855 Mr. J. Clerk Maxwell suggested and
tried the employment of red and green glass simultaneously, which frees it from Wilson's objections. He says, as to the effect of colored glasses
on the color-blind, -
" Although they cannot distinguish reds and greens from
varieties of gray, the transparency of red and green glasses
for those kinds of light is very different. Hence, after finding a case in which red and green appear identical, on looking through a red glass they see the red clearly and the
green obscurely, while through a green glass the red appears
dark, and the green light. By furnishing Mr. X. with a red
and a green glass, which he could distinguish only by their
shape, I enabled him to make judgments in previously
doubtful cases of color with perfect certainty. I have since
had a pair of spectacles constructed, with one glass red and
the other green. These Mr. X. intends to use for a length
of time, and he hopes to acquire the habit of discriminating
red from green tints by their different effects on his two
eyes. Though he can never acquire our sensation of red, he
may then discern for himself what things are red; and the
mental process may become so familiar to him as to act unconsciously like a new sense."
It is very generally remarked of and by the
color-blind, that they can distinguish reds and
greens better by artificial light than in daylight.
Many a one has avoided detection by carrying objects, especially goods, to the gas to enable them
to determine. The simple reason of this is that
they can see, as the normal-eyed, blue, and its complement yellow. The artificial light adds the yellow, and increases the yellow in the object itself,
thereby assisting their vision. In lesser degrees
of color-blindness this result is very marked.




128


COLOR-BLINDNESS:


Wilson found that the whiter and more intensely
luminous artificial lights, such as the lime-ball and
the electric charcoal-light, induce the same confusion in the perception of colors as sunlight does.
He says, -
" The contrast in appearance under the opposite illuminations is so great, that, among the cases of color-blindness
which I have recorded, there are as many as six persons who
have discovered that they could mitigate their peculiarity
of vision by the employment of artificial light. Thus Mr.
N., Professor Y., and Dr. E. have resorted to candle-light
as a means of increasing their enjoyment of flowers, which,
if crimson, appeared, when seen by it, much richer in color
than by daylight. Dr. E. and I had admired flowers together for years without my discovering his color-blindness.
Mr. N. states that ' it is quite an~enjoyment' to him to look
at crimson flowers by candle-light. Professor Y. has always delighted in going into a conservatory by candle-light,
because then all the purple and red flowers stood out in such
brilliant contrast to the green leaves.  A gentleman who
deals in colored goods has long been in the habit of appealing to a gas-flame in a dark room to decide between scarlet
and green, and crimson and blue."
Hence Wilson proposed for the color-blind such
colored glasses as rendered sunlight nearest to
artificial light. These are pale yellow or orange,
stained with oxide of silver. Such glasses were
supplied to the above-mentioned gentlemen. There
were four shades or depths of the yellow color.
One reported, " The glasses deepen, or rather
brighten, the reds, but do not affect the greens so
much. I can distinguish the reds by the aid of the
glasses much better than I can the greens. On a
bright day they gave a decided and very marked
difference between red and green. Scarlets it made
very bright and light; while crimsons were made




ITS DANGERS AND ITS DETECTION.          129
decidedly red and fiery." Another found he could,
through the yellow glass, see the same difference
between green and scarlet, and crimson and blue,
as by artificial light. The color-blind, therefore,
can assist themselves and avoid mistakes by selecting and looking through such yellow glass as renders daylight nearest to artificial light.
An interesting notice of a red-blind having discovered his ability to see better by lamp-light is
given by Dr. Minder.    The person was a member
of the Bernese family, whose color-blindness, from
documentary evidence, has been known to exist
two hundred years. In a letter dated Paris, 1799,
to his color-blind brother, he says, -
" You will find enclosed a pretty Swiss cockade. I have
separated it, but you can readily put it together. In the
centre is the yellow, then red, then green. Formerly, if I
had been torn on the rack to get this arrangement from me,
it would have been useless. About a year ago, however, I
made the brilliant discovery, that by lamp-light I could distinguish the colors. Rose-red, which by daylight is blue to
me, then appears a bright carmine; green, which by day is
red, appears blue: so that, give me twenty-four hours, I
should seldom be deceived. Write me if you have ever
made this discovery."
In March, 1878, Professors J. Delbceuf and W.
Spring of Lille published a very interesting and
important article on the amelioration of colorblindness by looking through certain colored solutions. Professor Delbceuf is color-blind; and hence
his observations, guided by Professor Spring who is
normal-eyed, are of such value, that I will give here
quotations from  the original article.   Delbceuf's
theory as to color-perception, deduced from his
results, is not of course in place here. I would




130


COLOR-BLINDNESS:


only mention that he endeavors to disprove the
Young-Helmholtz theory.
After various trials with one and another colored
fluid, he hit upon "fuchsine " five parts in weight
to fifty thousand d'eau alcoolis&e.  This he placed
in a wedge-shaped glass receptacle, with sides
meeting at one end, and separated at the other a
centimetre.   Thus he could look through any
thickness up to a centimetre. He employed other
strengths, but the above gave the best results.
Of these results he says," The effect obtained was marvellous: not only did the
colors which I usually confound - blue, carmine, and violet
on the one hand, and scarlet, red, and brown on the otherappear very different, but the scarlet red especially assumed
a brightness wholly unknown to me heretofore. It had appeared to me dull, but suddenly it became flaming and
brilliant. This was to me an extraordinary and unlookedfor result. The same effect was produced on two of my
pupils who were color-blind, and on those whom Professor
Spring and I have examined."
Professor Delboeuf found, in brief, that the
fuchsine corrected the usual mistakes as to red
fruits and flowers, the foliage, &c. With Professor Spring he also tested himself with large
numbers of pieces of colored silk.
" Two of the ribbons were of special service, -a marked
brown, which I had confounded with a bright scarlet red;
the other, a violet, which produced on me precisely the same
effect as a pure blue. The fuchsine showed me the difference between the colors and their shades with more or less
distinctness, and we found the same with the two colorblind we tested.
"I had here, then, a positive fact, and reason to suppose
that the fuchsine rendered my vision like the normal-eyed.
But this was a presumption I had to verify by producing
color-blindness in the normal-eyed by some solution before




ITS DANGERS AND ITS DETECTION.           131
their eyes. The hazard which brought us the fuchsine did
the same for chloride of nickel one part, and twenty-five of
water.  Through a centimetre of this solution Professor
Spring found the violet ribbon looked blue, red identical
with brown, and nature assumed a certain uniform tint
without brilliancy.  Glass stained with copper has also
largely this effect of rendering the normal-eyed color-blind.
Holmgren called attention to this, and says, ' We may get
a good idea of the difficulty the color-blind have in sorting
colored objects if one tries to do the same through greenishblue spectacles. We shall see and sort the colors pretty
much as a red-blind does, and have the same difficulty as he,
or all who attempt to do that which they have not the
power to.' I have said that the fuchsine gave me a very
marked difference between blue and violet, brown and
scarlet, and that the violet and scarlet became always more
brilliant, whilst brown and blue retained their ordinary
aspect. Chloride of nickel does not affect the normal-eyed,
except as to red or violet; green, blue, yellow, remain, so to
speak, unaltered. The reverse holds true with us; namely,
considerable thickness of the green solution but slightly
interferes with the harmony of colors as I see them: and,
through weak solutions of fuchsine, the normal-eyed do not
see objects very differently from generally. Stronger solutions only render the violet brighter, and especially the scarlet, which becomes whiter.
"t We need now only see if the fuchsine re-establishes the
vision of a normal-eyed rendered color-blind by chloride of
nickel. This is the case. When a normal-eyed looks at
our silks through a solution of chloride of nickel sufficiently
strong to render the red and brown ribbons, the violet and
blue, appear either brown or blue, and then adds a proper
thickness of fuchsine, the colors regain their distinctive
characters.  So, also, a color-blind corrected by fuchsine
becomes again color-blind by chloride of nickel."
Professor Delbceuf remarks, in closing his paper,
"These researches have an epilogue.  Having determined the cause [as explained by his theory] of colorblindness, we should not have thought of broaching the




132             COLOR-BLINDNESS:
question of its treatment, had not a singular circumstance
caused us to believe in the possibility of its cure. I have a
painting of flowers, - a bouquet of poppies. What alone
always pleased me in it was the correctness of design, the
freshness of the flowers, and their true and natural appearance. Returning in October, after an absence of six or
seven weeks, I found a new charm in this painting. I first
thought this was, as is so often the case with works of art,
but a momentary caprice. Yet finding it each day more
and more attractive, I thought whether, by looking through
the fuchsine, and thus giving myself the sensation of red, I
could not now see distinctions which in reality were hitherto
powerless to act on my visual faculty. This conjecture is
the more plausible as, at the commencement of our experiments, I had looked at this picture with our apparatus.
This was my thought when, in the beginning of November,
I made some tests of the railroad-signals, to see if our
liquids were sufficient to render distinguishable the red and
green lights. The results were not conclusive. I had a
vague sensation that my naked eye could recognize distinctions formerly impossible for me. But towards the middle
of last December, whilst walking in the city, I noticed, or
thought I did, red lights a few hundred steps off. I approached them, and found they were dim lanterns to mark
an excavation in the street. It was the first time that any
such light seemed to have a distinctive color. Formerly I
saw no difference between the yellow and red lights, except
that the former were brighter, and the fuchsine had but
made them look alike. Much interested, I went over to the
American tramway, where the cars are lighted by red lanterns. I used to notice but little distinction between them
and the gas-jets; but to my surprise I recognized them quite
well, even at a distance. I thought I had perhaps corrected
my color-blindness. Some days after, when the weather
was dull, I took out the box of ribbons in my laboratory.
Formerly, on such a day, I should have unquestionably found
them identical in pairs; but it was no longer so. The brown
ribbon remained the same; but the scarlet struck me vividly
by its brightness. In no possible position could I confound
them, and the difference remains still quite marked. I
asked Professor Spring to attempt to deceiveme by showing




ITS DANGERS AND ITS DETECTION.          133
them to me singly; but he could not. This I could not say
of the blue and violet. I thought I noticed a certain variance, but did not feel assured of not being deceived. I have
therefore to improve in this direction; but, no doubt, my inexperience with the blue and violet is due to my sensation
of red not being yet very strong. In fact, the fuchsine
gives the red of my ribbon a color much stronger than I
have as yet recognized. It is probably a matter of time
and exercise. Some time after, I thought to ascertain if the
solar spectrum looked different from what it formerly did.
Going to my laboratory, and taking up the ribbons, I found
the red brighter than the brown; yet it seemed as if the
contrast had somewhat decreased lately. I looked, therefore, very carefully at the spectrum. I thought, at first, the
gradations more marked in the yellow, and hence, on the
whole, that there was no change. Accidentally, however,
turning my eyes to the ribbons, I still saw one was more
brilliant, and, on going to it, found it was the brown I It
was only after a time, and repeatedly gazing through the
fuchsine, that the red again assumed in part its relative
brilliancy."
The following very misleading notice, based
upon the above, I quote from "The Scientific
American," Dec. 28, 1878 (p. 408): —
" REMEDY FOR COLOR-BLINDNESS. -' La France Medicale' states that M. Delboeuf has found, that, if a person
affiioted with Daltonism looks through a layer of fuchsine
in solution, his infirmity disappears. A practical application of this discovery has been made by M. Javal, by interposing between two glasses a thin layer of gelatine previously
tinted with fuchsine. By regarding objects through such a
medium, all the difficulties of color-blindness are said to be
corrected."
More important still is a report from a committee of the Belgian Royal Academy to the minister
of public works in answer to certain questions.
Professor Delboeuf was secretary of this committee; and, owing to his supposed discovery of the
effect of a fuchsine solution, they report, -




134


COLOR-BLINDNESS:


" In all cases there can be attached to the engine an ap.
paratus which prevents even the most color-blind from possibly confounding red or green with any color, and which
would add to the contrast of the signals. The apparatus
would consist of a red and a green glass having the properties spoken of. When the engineer had the slightest doubt,
he need but look through these glasses. Looking through
the red, the signal of that color would become brighter, and
contrast more with the general visual field. On the other
hand, it would be weakened by looking through the green.
The reverse holds true of the green signal. This apparatus,
infallible for the day-signals, would be efficacious to a certain degree for the night-signals also, but perhaps less practical here."
On this point Dr. Magnus says,"Whether the method, lately proposed by Professor Delbceuf, of palliating or improving color-blindness by fuchsinecolored glasses, will prove of service, time must decide. Professor Delboeuf, himself color-blind, believes the method of
practical value, as tested in his own case. But, as we have
already pointed out, deception here is very possible; and one
may readily mistake for a cure of color-blindness the practice
which a color-blind has gained by any increased sensitiveness to shades of light in distinguishing colors. Moreover,
there has as yet been no practical experience with Delbceuf's
method. "
In order to fairly test Professor Delbeuf's supposed remedy or cure of color-blindness, I have
had the apparatus made as he directs in his original article. With the fuchsine solution I have
pretty carefully tested six color-blind, both red
and green blind, and of various degrees. Two of
these were physicians, who had not only paid a
good deal of attention to the subject, but also to
their own cases. The result was quite unsatisfactory. A red-blind, after carefully working with the
fuchsine solution, reported that he could obtain




ITS DANGERS AND ITS DETECTION.       135
but little more benefit than he did by gaslight, or
a pale, lemon-colored glass, which simulated gaslight. Hie, as they all, reported that the green
worsteds in Holmgren's test, or other objects of
this color, were darkened, and thereby the relation
of light and shade altered. This assisted him in
selecting them. The same darkening takes place,
of course, with the normal eye. We can see what
a change in light and shade is produced by even a
small amount of fuchsine, and thus understand
how much the color-blind may hereby gain; that
is, how much is added to their already highly developed sense of light and shade perception. A
color-blind person who had not studied his defect,
or the subject generally, might very readily mistake the help of the fuchsine solution for a change
of his color-sense, and suppose, also, that the comparative new world to him was something permanent, - this also more especially as the fuchsine
solution intensifies the reds, and allows a red-blind
to get a much better idea of the sensation red to
the normal eye. This is probably, therefore, the
explanation of Professor Delbceuf's enthusiasm
over his discovery. But those who have studied
the vision of the color-blind - particularly the
educated - can readily understand the fictitious
assistance of a change of light and shade, which,
as I have said, one of my color-blind soon found
out.
Professor Holmgren, some years before Delbceuf's investigations, discussed the effect of colored glass and colored solutions in rendering the
vision of the normal-eyed like that of the colorblind.




186


COLOR-BLINDNESS:


In a review of articles on color-blindness, published in the " Revue des Sciences MWdicales," October, 1878, Dr. Javal says of Delboeuf's method,-," I obtained sheets of gelatine stained with fuchsine, which
produced the same effect as Professor Delbceuf's solution,
and which were much more manageable. But, notwithstanding this better arrangement, I much doubt if this means of
correction of color-blindness has a great future; for the
majority of those affected are too habituated to live with
their infirmity to be willing to suffer the slightest inconvenience in correcting it. This correction will therefore be
only applicable to those persons, relatively few, whose occupation is such that their infirmity is a positive hinderance.
And from these should be excluded railroad employds,
pilots, &c., who are color-blind, as such must be absolutely
removed from posts where their deficient chromatic sense
may cause accidents."
In reference to Delbceuf and Spring's statements as to chloride of nickel in solution, - one
part in weight to twenty-five of water, - I must
say I have carefully followed their experiment, as
also with a stronger solution arranged as they
describe; but I obtained no such effect as they
report, - of thereby rendering the normal eye
color-blind. All normal-eyed with whom I have
tried it tell me the same. It did not interfere with
my sorting the worsteds with Holmgren's test perfectly. Looking through such a solution dulls the
red a little, but nothing more so far as I can yet
see; with which, as I said, others agree. Moreover, the effect of the fuchsine solution was not
negatived by it to the color-blind. I confess myself at a loss to understand Delbceuf's statements.




ITS DANGERS AND ITS DETECTION.


137


CHAPTER XIV.
DANGERS ARISING FROM COLOR-BLINDNESS.
THE mortification, inconvenience, and loss of
position or employment, from the lack of power to
choose proper or appropriate colors in dress and
costume, to distinguish and match colored goods,
to mix or use colored pigments, I have already
sufficiently described. The dangers to which the
community are subjected from color-blind railroad
employes and pilots will be explained in this chapter, and how and why these should be avoided by
the action of the community in protecting itself.
For instance, an engineer has run on one road for
some five or ten years without accident of importance. The superintendent requires him to pass
examination by an expert, who finds he is markedly
red-blind, and shows it most convincingly to the
officials of the road. It becomes known; and they
then do not, of course, dare to keep him in his
place. He is dismissed, to protect the community
from danger.
We need no better proof of the recognition of
the danger than the measures so rapidly taken
for the last two years on so many of the Euro



138


COLOR-BLINDNESS:


pean roads, and which are being initiated by the
others.
Our very practical American people have recognized the danger from numerous colored lights or
signal-flags in having gradually discarded them.
Many roads already use only red by night or day.
Green and red are, however, most generally used
to signify safety and danger. From  experiment
and experience I agree that they are right. We
cannot give up color for form by night. It is,
however, possible by day. Is the danger any less
great here in the United States? I believe the
danger from ignorance of its existence is not small.
The chief of the Brotherhood of Locomotive Engineers told me he had not heard of color-blindness,
although he had run an engine twenty years; and
asked me, with some feeling, whether I "thought a
man was fit to run an engine who could not tell
green from red."
— The Massachusetts Board of Railroad Commissioners reported to me (Feb. 17, 1877), that "the
subject of color-blindness is one which has never
come to the attention of the board;" and they
" have not known of the subject being investigated
in this country."
There is danger from color-blindness, also, from
the general and the scientific press never having
taken it up in discussion in this country. I am at
present unacquainted with any thing on this special
topic, except one or two brief articles in "The
Chicago Railway Review," " The Scientific American," and an occasional paragraph in some medical journal. So far as I know, the whole question
of color-blindness and its natural danger was first




ITS DANGERS AND ITS DETECTION.     139
publicly discussed by myself March 7, 1877, before the Boston Society of Natural History, and
previously at a scientific club, where the necessity
of a color-test examination was urged. I speak of
this only as showing, that, notwithstanding the
number of very competent ophthalmic surgeons in
the larger cities of the Union, the subject has
failed as yet to arise for discussion through their
efforts. We naturally should have looked to them
for warning from the danger, especially as their
daily practice renders them so familiar with colorblindness from injury or disease. The subject, I
confess, forced itself on my attention.
Thanks to the efforts of such men as Drs. Wilson, Favre, Donders, and Holmgren, railway and
marine collisions or accidents will now be investigated in relation to color-blindness; and when one
is proved amongst us, as they have been elsewhere,
to have occurred on this account, then the community will be suddenly awakened to a realization
of the danger they have always incurred, and corporations forced to make some effort to avoid similar accidents in future. Then will be brought forward the facts presented in this volume. And it
will be shown, that, through the efforts of some
railway surgeons and scientific men, the world has
been taught that color-blindness exists to a greater
or less degree certainly in one in twenty-five of the
whole male population; that this must hold good,
therefore, among railroad employ6s and mariners,
where it is a source of very great danger. Hence
a court or jury will not be slow to accept and
apply the verdict of the general community, that
the accident was preventable, and the corporation
liable.




140


COLOR-BLINDNESS:


The teaching the community cannot be done by
the single or united efforts of scientific men. By
examinations in the schools, a knowledge of colorblindness and its dangers can be disseminated, as
well as the individual warned of his defect. If the
medical, popular, and daily press would take the
subject up, as they did in Sweden, the railroads
would soon feel forced to act immediately in the
matter. It also would not be long before an international commission would be appointed, and
laws for the control of color-blindness in the marine personnel agreed upon.      Professor Wilson
closes his book with the following:
" The professions for which color-blindness most seriously
disqualifies are those of the sailor and railway servant, who
have daily to peril human life and property on the indication which a colored flag or lamp seems to give. Fortunately a ship is seldom under the guidance of a single person;
and in her majesty's vessels the color-signal men are selected
from a large number, and are ascertained to have a quick
eye for color. In merchant-ships the choice must necessarily
be made from a much smaller number; and the appalling
yearly list of lost vessels which appears in our wreck returns awakens the suspicion that more than one of these
fatal disasters may have resulted from the mistaken color
of a lighthouse, beacon, or harbor-lamp, which on a strange
coast, hnd with perhaps the accompaniments of a snow-storm
or a thick fog, has been wrongly deciphered by a color-blind
pilot.
" On railways the danger attending mistakes of signals is
much greater than at sea; especially in this country (England), where trains travel at a very high rate of speed, and
succeed each other at very short intervals.... I am happy
to say that the publication of my papers has induced the
Great Northern Railway Company to require that in future
all their porters shall be tested as to their freedom from
color-blindness before they are admitted."




ITS DANGERS AND ITS DETECTION.           141
The attention of railroad managers, and also
that of the community at large, has in Europe
been repeatedly called to the great danger likely
to arise from color-blindness. I would, for instance, refer to Noel, in the "Courier des Sciences;" and I would particularly call attention
to the efforts of Dr. A. Favre of Lyons, France.
I cannot do better than quote from the r6umm6 of
his memoirs. He says, -
" I have proved, by facts personally observed from 1855
to 1873-77, the necessity of testing for color-blindness all
candidates for railroad service, and the exclusion of those
who are red-blind; also the necessity of specially examining
employds who have been injured about the head, those recovered from severe illness, smokers, and drinkers. I call
also for the periodic examination of all in active railroad
service. The majority of these precautions, adopted on the
Lyons road since 1857, have been gradually enforced on
other lines, and quite recently, also, on the Belgian roads.... Feb. 8, 1875, I called the attention of the ' Conseil de
Santd des Armees' to the use of the colored signals employed in war, and the necessity of testing those giving or
receiving orders by colored signals.... In February, 1875,
I called the attention of the Medical Society of Lyons to
color-blindness caused by injuries.... On Nov. 4, 1875, I
addressed the Medical Society of Marseilles in reference to
color-blindness in navigation. My conclusions were adopted,
and communicated to the marine authorities of the port and
the minister of marine. At the same time the Academy
of Sciences and Letters of Lyons voted to call to my publication the attention of the ministers of public instruction,
public works, war, and marine."
Wilson says, -
"The majority of even color-blind persons are able to
distinguish bright red from bright green when they are
near the eye and well illuminated: but this power of distinguishing between these colors diminishes with great rapidity when they are removed to a distance from the eye;




142


COLOR-BLINDNESS:


so that a separation of a few feet or a few yards, according
to the severity of the case, abolishes all sense of distinction
between red and green. As the colored day-signals on railways - especially the flags, which alone are available in
some of the most pressing emergencies -soon tarnish and
darken, the effect of time is to change light reds and greens
into much darker shades, and thereby continually to diminish
the distance (small at the best) at which the two dangersignals can be distinguished from each other by a color-blind
observer."
The danger, therefore, depends on the number
of color-blind employed on the railroads. They
have been found as frequent there as elsewhere.
My friend, Dr. Edmund Hansen, a distinguished
ophthalmic surgeon of Copenhagen, Denmark,
writes me, June 24, 1877, -
" The railways of Denmark are in the possession of two
parties: one is a private company, which owns the railways
of the larger island called Seeland, and of the adjacent
smaller islands, Laaland and Falster; whereas the railways
on the island Funen and on the peninsula Jutland belong to
the government. The investigation for color-blindness has
just been completed by the private companies: on the government railways it will be done in the course of the summer.
(I will give you the results of the private company, and
shall send you the other when the results have been made
known.) The examination on the Seeland, Laaland, and
Falster roads has been made according to the method of Professor Holmgren. 1,084 persons were examined, of whom
50 were women. Of this number, 31 men (or 2.87 per
cent) were color-blind, -all congenital cases. None of the
women were color-blind. Of the 31, 10 were perfectly colorblind, 21 imperfectly. Of the perfectly color-blind, 6 had
red-blindness, 4 green-blindness. Their occupations were:
2 station-masters perfectly green-blind; 1 engineer perfectly
red-blind; 1 train-conductor, 1 fireman, perfectly greenblind; 4 porters, 3 blacksmiths, 7 railway guards, of whom
2 were perfectly red-blind; 2 assistants, 1 pupil, perfectly
red-blind; 1 concierge, 2 foremen, of whom 1 was perfectly




ITS DANGERS AND ITS DETECTION.     143
green-blind; 4 workmen on station, 1 perfectly red-blind; 2
extra conductors, 1 perfectly red-blind."
These examinations, I understand, were made
by Dr. Fontenay.
Professor A. Quaglino, of Milan, Italy, writes me,
Aug. 11, 1877, "I do not know whether there
are any statistics of color-blindness published in
Italy, though I am sure that all the railroad employes are subjected to a rigorous examination in
reference to their color-perception."
Dr. J. Stilling, of Cassel, also writes me, Dec. 6,
1877, "I have but once had opportunity of examining railroad employ6s, about four hundred in
number. Of these, six per cent were color-blind."
Dr. Magnus reports the result of one of his colleagues on a Breslau road as four per cent of colorblindness among the employes.
Professor F. C. Donders of Utrecht, Holland,
with the assistance of twelve physicians and
ophthalmic surgeons, whom he had specially instructed in a method of his own, examined 2,203
employds on the Holland roads. He found 152 of
these more or less color-blind. These he subsequently — with his assistant, Dr. Bouvin - still
more carefully tested, thereby confirming his previous results.
Dr. A. von Reuss writes me March, 1879, having
found 3.50 per cent color-blind among 800 of the
employes of one of the Vienna roads.
I have perhaps quoted enough to show by statistics, and by the precautions railroad corporations
in Europe are taking, the extent to which colorblindness prevails amongst employ6s, and its consequent danger. But I should quite fail in giving




144


COLOR-BLINDNESS:


the subject due prominence as to the prevalence
of color-blindness, the value of scientific investigation in detecting it, its danger for the community, and the success of true methods of testing
in convincing railroad people of all this, &c., were
I not to quote from Professor Holmgren's work.
He says, -
" In a case called the Lagerlunda, arising from a railroad
accident at Lagerlunda, in Ostrogothia, Nov. 15, 1875, and
which excited great public attention, there was evidence
leading me to suppose that color-blindness was one of the
principal causes of the disaster. This led me to think that
control should be exercised among railroad employds as to
color-perception.
" In June, 1876, I had an opportunity for testing this matter. By the courtesy of Major-Gen. von Knorring and
Major Rudbeck, I was permitted to examine 2,200 men of
the infantry and dragoons of the guard in camp in Upland.
From this examination we learned, in reference to the existence of color-blindness among the population of the
province, that, out of the 2,200 men, 11 were red-blind, 17
could not perceive green, and 1 violet (?); 31 besides were
incompletely color-blind in accordance with my classification.
There were, then, 60 defective, or 2.7 per cent. The cases
of ' feeble sensation of colors ' are not here included.
"July 14 of the same year I had opportunity, at the
Scandinavian Medical Congress assembled at Gothenburg,
to describe my method, report the results of its employment,
and also to express my views as to the necessity of taking
measures on a large scale in reference to the detection of
color-blindness, especially among railroad employds. In
consequence the congress voted unanimously on the necessity
of instituting examinations to detect color-blindness, first,
among railroad employes; second, among pilots, lighthousekeepers, and sailors in general; and, third, in the schools.
During the congress I had time to show the physicians the
practical application of the method, by examining in their
presence, by permission of Col. Carlsohn, 100 men of the
artillery regiment in Gotha, amongst whom we found 4




ITS DANGERS AND ITS DETECTION.            145
color-defective,- 1 for red, 1 for green, and 2 incompletely
blind to color. At the same time I found one green-blind
among the physicians, members of the congress, and one
ted-blind among the assistants.
"cI was then prepared to apply directly to the railroad
administration. Thanks to the press, which followed attentively the discussions in the congress of Gothenburg, the
question came to the knowledge of the public. It naturally
attracted the attention of the railroad officials, who for the
most part looked upon it with a certain distrust, as rather
the result of learned imagination or over-solicitude than as
a practical matter for the railroad service. We have heard
a railroad official use almost literally these words: ' If
color-blindness really exists, it cannot be amongst the employes, or it would have been noticed. This must at least
be the case with the engineers and conductors, all of whom
obtain their places after passing through inferior grades,
and consequently after having sufficiently proved their faculty of distinguishing colors.' It was, therefore, very important to obtain some certain data on this point. This soon
arose. Mr. Jacobsson, chef d'exploitation of the Upsala-Gefle
line, asked me to accompany him on a tour of inspection,
and examine all the employes under his orders. The tour
was undertaken in the fall. We left Upsala Sept. 7, and, to
carry out our examinations, halted at all the stations, at all
the guard-houses, and at every gate; in short, we stopped at
every point where an emnploye was to be found. The examination was finished at Gefle Sept. 8. All the force - 266
men and women -were tested. Amongst them we found
13 defective; viz., 4.8 per cent. Six were completely greenblind, and 7 incompletely color-blind. Their positions were,
1 chief of station, 1 engineer, 2 conductors, 1 chief of equipments, 2 men of the equipment department (one a supernumerary), 2 overseers, 2 road-guards, 1 clerk, and 1 stoker.
Immediately after the examination, the chef d'exploitation
dismissed all those who were blind for green.
"This first expedition was interesting in many respects.
It showed that the method of examination was adapted to,
and could be used on, the railroads. It showed, moreover,
that there were really color-blind, in nearly every degree,
employed on the Swedish roads, of which no one had had
the slightest suspicion."




146


COLOR-BLINDNESS:


Professor Holmgren reports later in September,
1878, having to date tested 7,953 railroad employ6s,
and found 171 color-blind, or 2.15 per cent; viz,,
45 red-blind, 48 green-blind, and 70 incompletely
blind.
" In Finland Dr. L. Krohn, who was by correspondence
instructed in the method and principles applied in Sweden,
has already examined the personnel attached to the railroads of his country. A locomotive and car were placed
at his disposition to enable him to test the employes on the
whole length of the line. It was completed in twelve days.
He found, among 1,200 persons tested, 60 color-blind; namely,
5 per cent. They were as follows: 4 red-blind, 25 greenblind, and 31 incompletely blind."
Professor Holmgren brought this matter before
the various railroad directions in Sweden. Moreover, experiments were made in the Physiological
Institute at Upsala; so that, by Nov. 9, 1876,
throughout Sweden, it was ordered that all the
railroad employes should be tested for color-blindness by the methods there used.   What Professor
Holmgren has accomplished leaves no excuse for
our American railroads in hesitating or refusing to
thoroughly and properly test all their employds for
defects of color-perception, and dismissing those
who are color-blind, and providing also for the
future by testing all applicants for employment.
If long before this my readers have been astonished at the facts here collected, they, no doubt,
have also been equally disposed to question them,
or at least their practical bearing. They will naturally say, " We do not hear of railroad accidents
from color-blindness, and rarely of marine collisions attributable to this cause." Of this I shall
again speak; but I must first here explain how it is




ITS DANGERS AND ITS DETECTION.            147
that the color-blind employ6s get on so well, conceal their defect, and perhaps avoid accident. I
shall confine my remarks to the railroad personnel
and mariners. How the color-blind escape detection in every-day life, I have already fully described. Professor Holmgren explains this so readily from his experience, that I do best to first quote
from him. He says, -
"We should imagine a color-blind railroad employ6 would
be immediately detected, or would have at least discovered
his own defect. This very natural idea has greatly tended
to retard the reform we have called for. It is, however, incorrect, and does not stand the test. On the contrary, examinations showed that a large number of color-blind were employed in nearly all the positions on a railroad, without they
or others being aware of their faulty color-perception. And
further: a number of these, far from being convinced of
their defect, even after the examination, insisted on repeating the test (even six or seven times), giving all sorts of
excuses in explanation of their constant mistakes. They
all agreed in saying that they had excellent sight, never had
experienced the slightest difficulty in distinguishing the signals, and though a long time in service, and in most important posts, as locomotive-engineers for instance, never had
made the slightest mistake.
" Certainly we may well be astonished at this condition
of things, and very naturally ask how it is possible for any
one to perform the duty of engine-driver, for instance, any
length of time without exposing a deficiency of vision so
important for the performance of this duty. There are, so
far as we know, only two explanations: one is in the peculiar visual sense of the color-blind, and the exercise of this
sense in distinguishing the signals; while the other depends
on the conditions under which an engine-driver ordinarily
does duty.
" As to the first explanation, we must remember that every
color coming from an illuminated colored surface may be
more or less bright or dark, and every lantern-light, even
colored, may be stronger or weaker. Hence, in a colored




148              COLOR-BLINDNESS:
object or colored light, the eye does not alone take note of
the color or quality of the light, but also of its quantity or
intensity. When two objects or two lights appear of the
same color to the eyes of a color-blind person, they may
differ as respects intensity. This being the sole difference
between these lights, it is particularly noted; and thus,
often as a result of special exercise, such color-blind person
may strengthen his perception so as to in a certain degree
make up for his color-deficiency. He resembles somewhat
the persons who, deprived of one sense, replace it to a degree by the greater exercise of one or more of their other
senses. We have already noticed this point, so very important in practice, but could not refrain from again reverting
to it here. Any one who has experience from conversation
with intelligent color-blind, or experimenting with Maxwell's rotating disk, will have noticed their peculiar sensitiveness to varying intensity of liqht whilst comparing two
colors, and hence can have no doubt as to how a color-blind
person can so often distinguish between railroad-signals, and
give the colors their true names.
" Did we not know this, we should be greatly astonished
to find with what facility a color-blind railroad employe can
distinguish between the red and green flag, and generally
call the red, green, and yellow lanterns by their right color:
but it is the intensity of the light, and not the color, which
governs his decision; and this is the whole secret. The flags
and lanterns have, in fact, usually a constant difference as
to intensity. The green flag is to the color-blind, as also to
the normal eye, undoubtedly of the deepest or darkest color,
and the red the most brilliant. As to the lanterns, the redblind always recognize the red light by its being darker than
the green, and the yellow by its being clearer or more brilliant than the other two. The green-blind finds also, in his
turn, the red more brilliant than the green, and distinguishes it by this.
" The other explanation lies in the conditions under which
an engineer has to observe the signals. First of all, we
must remember the great regularity with which all the
details of railroad service take place. An engineer starting
from a station at one end of the line knows very well in
advance what stations to stop at, and which to pass. Under




ITS DANGERS AND ITS DETECTION.           149
ordinary circumstances he knows which light ought to be
exhibited on the signal-posts above the several stations.
The hand-lanterns are not as important, since their color is
not so essential, being supplemented by movements. Hence
it is only under exceptional conditions that accidents can
happen at stations from mistakes as to the color of fixed
lights. There may, of course, be a number of other cases
exceptional to the ordinary regularity: but we must here
notice one circumstance, which probably has been and still
is of very great importance; namely, that the engineer is
not the only one who has to watch for the signals. There
is always with him the stoker, and near him a conductor, an
oiler, &c., to aid him at critical moments. It must be extremely rare that all the personnel of a train are affected
with color-blindness.
" Considering only practically the fact mentioned, and the
explanation we have given, one might perhaps imagine that
color-blindness had some scientific, but hardly any practical,
interest, and hence that all the talk that has been made
about its existence among railroad employes in our country
was unnecessary; because, as may be said, the color-blind
have often been employed a long time in railroad service
without its being noticed, and without accident or the slightest inconvenience arising; and finally, that, since they can
really distinguish the signals (although this is otherwise than
by color), their kind of blindness need not call for any preventive measures. It is thus that a great many persons still
reason.
" We do not stop here to give the testimony of experience
on this point in our country. One fact is certain; namely,
that color-blindness in other countries has caused numerous
and very fatal accidents. Even if this had not been definitely proved, it is none the less evident that we have no
right to await another such experience before passing to
words and acts, and in every way showing, that, notwithstanding the numerous circumstances which assist the colorblind in responding to the signals, danger is not wholly
avoided, and the uncertainty remains. This is readily
shown. Neither the fact that the color-blind have been
employed many years on the railroads without causing accident, or even without their defect being discovered, nor




150


COLOR-BLINDNESS:


the circumstances we have cited in explanation of this fact,
furnishes the least assurance of security.
" A typical color-blind person cannot distinguish between
red and green. This is an incontestable fact, readily explained by theory, and sufficiently proved by experience.
All his judgment as to the difference of colors rests, in consequence, on conjecture. If, perhaps, exercise enables him,
up to a certain point, to distinguish between the red and
green railroad lights, this is dependent on the intensity of
the light telling him the color. But there is, of course,
great uncertainty in this means of reading the signals; and
the man who may be right in a certain number of special
cases will surely go wrong in some other. It is a principle
not dependent on theory, but confirmed by our experience in
examining more than two hundred color-blind; and we may
extend it beyond the limits we have here kept, - in other
words, to the majority of cases also of incomplete or partial
color-blindness.
" That the situation of the color-blind in respect to signals may be thoroughly understood, we must here add a few
important words on the point. What is the intensity of
light? Strictly speaking, it is nothing but the force of the
impression of the light which our eye receives. This, however, is dependent on two factors, -one, the quantity of light
radiating from the object observed or reflected by it; the
other, the strength or amount to which the eye re-acts to
this, or, in other words, the sensibility of the subjected visual sense. We may readily understand that both of these
factors are extremely variable under the circumstances of
the engineer's service. The amount of light which comes
to his eye depends naturally on the amount reflected from
the colored object, or which, for example, radiates from a
railroad-lantern. It is very evident that this quantity may
vary from many causes, such as the nature of the illuminating material and the wick, the coloring matter of the glass,
its thickness, the peculiar property of the glass, &c. If a
little moisture or smoke, vapor, ice, snow, &c., adheres to
the glass, the lantern is less luminous. A lantern illuminates differently in clear from what it does in foggy weather.
All this may give rise to mistakes. But, on the other hand,
the sensibility of the eye differs greatly under different cir



ITS DANGERS AND ITS DETECTION.           151
cumstances. The nervous apparatus of the eye may, like all
other parts of the system, vary in its sensitiveness. The
same light is brighter to a healthy eye in repose than to an
eye fatigued and weakened. Every modification of the intensity of the light is, however, for the color-blind a change
in color. From this we may judge how little dependence
can be placed upon a recognition of the signals which the
color-blind gain from exercise.
" Hence, if we admit among a large number of color-blind
an extraordinary faculty gained by the exercise of the eye
with different degrees of intensity of light, we must equally
deny that this is sufficient for the security of the roads, as
we cannot be assured of all the lantern-flames being of the
same strength; all the glass of the same kind, of the same
thickness, purity of color, allowing the radiation of the same
quantity of light; and, finally, of the eyes of the employds
being always at rest to the same degree, this being practically impossible. No person in his senses would deliberately trust his life in the hands of an engineer who could
only distinguish the signals by the difference in the intensity of the light. Ask any superior official of a road if he
would be willing to take charge of and run a locomotive,
assuming the responsibility, when -uncolored signals alone
were permitted, and a feeble light meant ' danger,' a medium
one ' attention or caution,' and a strong one ' road clear.' If
he says no, tell him that these are just the conditions under
which every color-blind engineer has performed his duties.
The absurdity is evident at once.
" The aid an engineer can expect from those within his
reach is as little to be depended on as the intensity of the
light, especially as he himself is directed to observe the
signals, and is responsible for what happens. Without noticing all the possible cases when he may at the moment'of
danger find himself without help, it will suffice to mention
but a single one; namely, when his neighbors are also colorblind like himself.
"To sum up: we may grant that a number of circumstances concur in rendering railroad accidents from colorblindness of the personnel relatively rare, even when no measures have been taken to avoid them, and experience has
fortunately confirmed this opinion; but, on the other hand,




152              COLOR-BLINDNESS:
it is self evident that such accidents may happen sometimes.
Here also experience testifies; and there are probably many
more accidents due to this cause than those proved to have
so occurred. Under these circumstances it is the absolute
duty of railroad managements and maritime authorities to
look to it that no measure which can aid in avoiding the
possibility of these accidents shall be neglected, and to do
all in their power to guard the lines of communication in
the land and on the sea against all the dangers which
menace them."
Direct testimony on these points is of so much
value, that I quote from Dr. Magnus, who says, -," I knew an engineer who was red-blind. Red and green
were absolutely undistinguishable to him; yet he could tell
the red from the green signal, from having cultivated his
perception of the difference in the intensity of the light.
However valuable this capacity may be for the individual
color-blind, there is danger in it. It may happen - and, no
doubt, often does - that the color-blind, by the cultivation
of their power of appreciating varying intensities of light,
conceal their defect, and induce their surroundings to suppose that they are normal-eyed. But this cultivated power
of distinguishing the lights by difference of intensity must
always be a very unsafe artifice, which succeeds a hundred
times to fail the hundred and first. It is, therefore, a very
critical thing for a color-blind railroad employe- for instance, an engineer - to be able to conceal his defect for any
length of time. So long as he does, so long are the trains
in danger under his control; for how readily may his artifice
fail him by which alone he distinguishes the red and green
signal-lanterns from each otherl Only the most careful examination of all railroad employes can protect the public,
which, thanks to our railroad authorities, is now conducted
on all the German lines."
Dr. Minder, in Berne, reports among his cases
that of "a very intelligent young man who was
red-blind, but was not aware of it. He held the
position first of fireman, and then of engineer,
on one of the Swiss roads. He was hardly at




ITS DANGERS AND ITS DETECTION.    153
work before his defect troubled him. Thinking it
was due to the spirit he drank, he stopped this for
a while; but, the trouble continuing, he became
convinced that 'something was wrong with him
about the colors,' and left the distinguishing
the signals to his normal-eyed assistant. When
another man took this assistant's place, - who also
seems to have been color-blind, - the work began
to be 'uncomfortable.' As our red-blind engineer now had no control by his side, and very
frequently was mistaken in his decision, there
occurred a series of mistakes, fortunately only
whilst manoeuvring in the stations, which brought
him occasional fines and other disagreeable consequences.
"The red signal-lantern gave him the most
trouble, because, as he said, he could only distinguish it when so near with his engine as not to be
able to stop, and hence run by it. He did better
with the green signal; and, when asked why, replied, ' Because it was brighter.' To the question
how, then, could he tell the green signal from
white, he, in a roundabout way, compared green
to weak white; and stated, that, with a lantern of
white glass, he could, by screwing up and down
the wick, and thereby changing the amount of
the light, himself imitate the usual railroad-signals. Very bright light was white; very weak
light, red; medium intensity, green, -quite corresponding to Holmgren's statements based on
theory. The seeming impossibility of his power
of distinguishing being dependent on the amount
or intensity of the light, induced me to search
farther, and ascertain what a complete color-blind




154


COLOR-BLINDNESS:


understood by pure white. I found for this, also,
much greater color-sense than the normal-eyed
possess. A whole series of color-blind were expressly asked to select only the purest white.
Of worsteds and papers they picked out, besides
the white, several shades of bright green, gray,
pure gray and dirty gray, light rose, and very light
violet.
" The possibility that a color-blind may, through
his life, under favorable circumstances, remain
undiscovered, and as engineer or switchman perform his duty, cannot be denied. That the filling
such posts by the color-blind, however, is a constant source of danger, can be readily understood. For instance: a white lantern exposed to
the weather by snow or rain, by the absorption of
light from the dimmed glass, may appear green
to a color-blind who depends upon the intensity
of the light alone. So also a green light may give
the impression of a red one. By the accidental
use of thicker or darker green glass, or thinner
and brighter red glass, the difference in the intensity of the light may also be destroyed; and hence
arise all the conditions for the occurrence of
dangerous mistakes."
There is a point in reference to steam worth
mentioning here, - viz., its varying color; and
hence its possibility of causing mistakes. Professor Forbes, in 1839, noticed the sun, through a
column of steam from the safety-valve of an engine
on the Greenwich Railway, of a deep orange-red
color. This he again noticed on the Newcastle and
Carlisle road, and it induced him to experiment
with white lantern-light seen through escaping




ITS DANGERS AND ITS DETECTION.        155
steam. It appeared red under certain pressure of
the steam, and also green or violet under other
pressure. Mr. R. Phillips, in 1852, followed this
up, and found that the transmitted light was red;
and the reflected, blue. As to this, Professor
Wilson well remarks, "Now it must often fall to
the lot of engine-drivers to watch lamps through
such an atmosphere, which will convert the (white)
safety-signal into a danger-signal, completely alter
the color of the (green) caution-signal, and so
darken the aspect of the (red) danger-signal as to
render it invisible."
To the even very slightly color-blind this will
be intensified, and to the completely color-blind
his only means of distinguishing the signals will
be gone; viz., the difference in the intensity of
the light.
One of the dangers from color-blindness on our
railroads arises from the supposed cure or palliation of it by exercise of the personnel with the
colored signals, &c. Upon this latter point I dwelt
when discussing the incurability of congenital
color-blindness. It becomes therefore necessary
to here criticise Dr. Favre's ideas and proposals in
reference to such exercise. The whole matter,
however, is put so practically by Professor Holmgren, and is of such importance, especially in this
country, that I shall quote from him. In his criticism of Dr. Favre's ideas, after speaking of the
various ways the color-blind supplement their defect, he says, -
" The. color-blind railway employ6 has always a certain
assistance at his disposal in distinguishing the flags by day:
for he sees not only the flags, but also the person who holds




156              COLOR-BLINDNESS:
them; a green grass-plot, a tree, a house, -in short, objects whose color-name he already knows. The importance
of this is the greater from what we know of the value of comparison in the use of our other senses, and hence, also, of our
color-perception.
" From this it might be judged that it was a matter of
indifference whether the color-blind could be cured by exercise with colors or not, so long as they can by other means
distinguish the signals. We admit they are thus by day
less liable to mistake them; but we cannot grant more. The
color-blind can, however, never be sure, since they can never
calculate beforehand all the circumstances leading to mistakes. Sunlight on a green flag, with the surroundings in
the shade, makes it appear red to them; or, what is worse,
the red flag on a bright day, when in the shade and the surroundings bright, will appear green.
"The condition is much worse with night service. No
comparison is then possible. Only the light itself is now
visible; and what adds to the difficulty of distinguishing
the color of a lantern as compared with distinguishing a
colored surface, is our accustomed way of using our senses.
In fact, we do not take cognizance of the action of our sense.
We do not ever think of the light radiating from or reflected
by the object: we rather refer all these to the object itself,
and regard them as inseparable attributes of it. We recognize the light of the lantern, without thinking of the
material on which it depends. We do not see the lantern
or the flame burning in it, but only the light which has
neither the form of the lantern or the flame, but is isolated
and immaterial in the air. Now the color-blind must distinguish whether this is strong (colorless), medium (green),
or weak (red). This is asking more of the human eye
than it can do with certainty."
"The color-blind are therefore more often mistaken in
distinguishing colored lights than colored surfaces. If we
show them one of the lanterns, they cannot distinguish it,
unless previously practised. Showing them the red and
green together, or in rapid succession, they generally distinguish these from each other; and, if we tell them the names,
they remember and call them correctly. The red-blind find
that the red of the signal-lantern, such as used on the




ITS DANGERS AND ITS DETECTION.            157
Swedish roads, is darker (that is, weaker in light) than the
green. The latter, however, seemed to them darker than
the common yellow light. The green-blind, on the other
hand, find that the green light is weaker (that is, darker)
than the red. With the next opportunity these color-blind
find the same.  Railroad employes are therefore rather
more sure; yet much is dependent on the special lanterns
used. One familiar with the nature of color-blindness will
do better to use lanterns with different glass from that commonly employed, when desirous of exhibiting the precise
character of this defect. Let him take one with a thin
pale-red glass, and another with thick dark-green glass.
The color-blind will then readily take the green light for
red, and red for green or colorless.  If the glass of the
green light is smoked, he will take it for red. Cover the
colorless light with steam or dew, and it appears to him
green. Or let one do as I, - namely, have lanterns, the
glasses of which are prepared for this purpose, and differ
from each other, some having colorless or so-called smoked
glass of varying absorptive power, - and they will quickly be
convinced that the color-blind is guided in his decision
solely by the intensity of the light.
"Another circumstance assists the color-blind in telling
the lantern's light at a distance, which is also dependent on
the intensity of the light, though this connection is not at
once seen. It is the varying way in which the light radiates outwards.  This radiation is most intense with the
ordinary lantern, since this is the brightest (strongest in
light); whilst, when the lantern-light is weak (red or
green), the radiation is very little or nothing. A color-blind
railroad employd told me he thus distinguished the signals.
It need be hardly said how unsafe this is."
"We see, therefore, that practice is of no avail for the
color-blind. Otherwise an employS, who has had daily exercise with the colored lanterns for a series of years, would
have been cured of his defect. A pretty wide experience
has, however, shown us that not one of the many color-blind
we have examined stood the test. We must confess that a
large number, from constant practice, had attained extraordinary facility, and frequently told the colors correctly."
"As a proof that comparison plays such a strong part, it




158             COLOR-BLINDNESS:
is often necessary to make special choice of the particular
lanterns for the test. If we use the ordinary lanterns, the
color-blind will only make mistakes at the commencement.
If they see all the three lantern-lights together, they are
deceived much more seldom. A colorless glass, with moisture on the surface, will at first be readily taken for green;
a smoked green glass, for red."
There is another peculiar danger on railroads.
A mixture of the two complementary colors, red
and green, necessarily employed, produce white
light. This, of course, does not affect the colorblind in the same way as the normal-eyed; yet it
adds to their confusion. The law of the mixture
was naturally well-known; but Mr. W. H. Tyndal,
in 1853, first, I think, called attention to its very
practical bearing. He says, -
" Now, we have this curious fact, that on the railways the
union of the two colors - the primary red to indicate danger,
and the secondary green to denote caution -together makes
white, the signal for entire safety. This, perhaps, does not
practically appear in experiment, when the mind is on the
alert to distinguish between the two colors. If the rays
from a green lamp, such as are used on railways, are thrown
upon a white board, and those from a red lamp are directed
to the same spot, - the distance of the two lamps from the
board being equal, -the red rays, though rendered paler,
predominate. There is, in fact, too much red. But the
red lamp may be removed so much farther from the board
than the green one as to allow the green rays to predominate;
and there must be a point of distance where neither color
would predominate, and at which the mixture of the rays
on the board would be white. I recently made an experiment on one of the metropolitan railways with a green and
a red signal-lamp. A man was stationed at the end of a
tunnel, about four hundred yards long, and directed to wave
the two lights together. The pointsman at the other end, not
knowing any thing of the nature of the experiment, was
asked what light was waved. He was satisfied it was white,
and could not be persuaded that two lights -a red and a




ITS DANGERS AND ITS DETECTION.          159
green - were really used, although the matter was afterwards
explained to him. Now, it may sometimes happen that, in
rapid travelling, the rays from a red lamp and a green one
shall flash together across the sight of an engine-driver; or
the unsteady motion of an engine may render the driver unable to see distinctly and separately two signals of different
colors, the rays from which may fall upon his eye in parallel
lines. In either case it is not improbable that the light
might be regarded by him as white. A light may be discerned without the color of it being distinctly seen. In
such case it would most likely be regarded as white, - that
being the most common. It is not improbable that some of
the accidents which have occurred in railway travelling have
arisen from the colors of the lights shown being indistinctly
seen; perhaps from a confusion of rays from two or more
lamps. In some cases most contradictory evidence has been
given as to the color of the signal shown. The subject is
perhaps worthy of the attention of railway engineers."
The following is an interesting proof of how a
shrewd observer may, from lack of knowledge of
the peculiar condition above explained of the
color-blind's perception, fail to explain cases presented to him: -
Mr. Thomas Nelson, an optician in Chicago, Eli.,
in an article in " The Chicago Railway Review " of
March 30, 1878, says, -
"I have kept records of various accidents that have occurred, both upon land and water during the past few years;
and I have gathered such information about some of them as
I could get outside of official sources. Often I was unable to
get any of any value; but I am convinced beyond a doubt
that a large proportion of them could have been traced to
color-blindness for a correct solution as to the primary causes
of the accident. The query has been made, that if these
defects in their various forms are as numerous and of such
a dangerous character as has been shown, how can we account for such a comparatively small number of accidents
occurring which might be charged to them? I have attributed it to the high average intelligence and acquired cau



160


COLOR-BLINDNESS:


tiousness of engineers and pilots as a class. They have become so accustomed to be on the lookout for danger, that
their suspicions are easily aroused, which creates a sort of
instinct that governs their actions, and they do not recognize
but that their perceptions are correct. My convictions in
this respect have been greatly strengthened within the past
few months, there having been related to me some experience with an engineer, who was continually making narrow
escapes; and, after watching his actions under different circumstances for a time, color-blindness was suspected, proved,
and afterward acknowledged by him. The correctness with
which he formed conclusions under the existing circumstances would indicate that he had some means by which he
was enabled to form a plan of action; but he declared that
he had nothing upon which to base his actions but the cautiousness acquired in that branch of service."
The means he had to assist him were of course
the to him varying intensity of the light, when red,
green, or white. This is an interesting proof of
how totally unaware a color-blind may be of the
way he supplements his chromatic defect, as also
how he may escape detection.




ITS DANGERS AND ITS DETECTION.


161


CHAPTER XV.
DANGERS FROM COLOR-BLINDNESS ON THE OCEAN.
IF we turn now from the land to the sea, we
shall find the dangers from color-blindness as
great, or even greater. The largest majority of
those color-blind are so for red and green. These,
however, are the colors necessarily chosen by all
nations to be by law carried on the two sides of
all vessels from sunset to sunrise, - the green
light on the starboard side, and the red light on
the port side. These are so arranged that they
can only both be seen when the vessel is directly
ahead, and far enough off to allow us to see both
sides. These lights show us, therefore, the position
and the direction of motion of a vessel. Mistaking
their color will of course be most disastrous.
Dr. Romberg has classified the reports of some
maritime accidents from 1859 to 1866. They
number 2,408.
Want of skill, or carelessness, of the ship personnel,
or the accidents which it was impossible to prevent
or avoid........ 1,562
Error of the pilot or captain.....   215
Want of observation or proper interpretation of the
rules of the way.......   537
Undetermined causes......    94




162


COLOR-BLINDNESS:


Under the last three heads, in the large number
of 846, there are probably some attributable to
color-blindness. They all are not accidents from
carelessness or want of skill; for those are included in another series.
M. L6once Raynaud and M. Degram have demonstrated the effect of fog on the color of lights.
Fog or mist makes white lights reddish. In thick
weather green lights appear white. A sailingmaster meets a green light rendered pale by a
thick night: in whatever amount he is color-blind,
in that degree will the light appear white to him,
causing most dangerous hesitation; or, even if
convinced he has not a green light ahead of him,
he manceuvres as if it were a red one. Colorblindness may therefore well be considered as one
of the causes of collision at sea. This imperfection may, however, occasion the loss of a vessel in
another way: I mean in the recognition of lights
on the coast, &c. Dr. Feris reports three cases of
such mistake from    the "Annales du Sauvetage
Maritime," vol. iii., 1873. He says,"If color-blindness is considered a grave danger on railroads, how much more on the sea! Colors are very important to the mariner: the flags, the side-lights, and even the
lighthouses and buoys and beacons, present various colors.
It is impossible for a helmsman or a signalman to interpret
or transmit signals if they have no appreciation of color.
Errors with flag-signals are not so likely on board of vessels,
as they are employed in daylight, and more often controlled
by officers in charge. But the men at telegraph-stations are
often alone, not under observation, and hence more likely to
make mistakes. National flags may be mistaken, but more
especially the white, red, and green Bengal lights used as
night-signals... If good color-perception is necessary for
a helmsman, how much more for the commander of a vessel I




ITS DANGERS AND ITS DETECTION.        163
The increase of collisions at sea is an indisputable fact.
How many remain unexplained, or referred to another
cause, which are no doubt due to the color-blindness of a
single man l "
The testing for color-blindness has already commenced in the navies of Prussia, Russia, Norway,
Sweden, Denmark, and Austria. My friend, Dr.
Ed. Hansen of Copenhagen, writes me, June,
1877," I have had the opportunity of examining a large number of the individuals who enter the royal navy: I hope
some day to be able to give you some statistical information
on this point, if you still take an interest in it."
Professor Holmgren reports as to the examination of 4,225 Swedish sailors, finding 94 (or 2.22
per cent) color-blind.
Dr. Lederer was appointed by the medical department of the Austrian navy to test sailors at
the naval station at Pola. He examined of the
sailors at the station and on the artillery schoolship "Adria" 1,312, finding 63 (or 4.8 per cent)
color-blind. There has been some misunderstanding as to his report due to his employment of Stilling's cards and pieces of colored glass and paper,
instead of Holmgren's infinitely more sure and
ready method with the worsteds.
Dr. Feris of the French navy found, among 501
officers and men, 47 "who presented in varying
degrees an alteration of the chromatic sense."
Their ages were between seventeen and fifty years.
Dr. Favre, in France, records the examination
of 1,050 men for the navy or lighthouse department, and finding 61 (or 5,8 per cent).more or less
color-blind. In discussing the question, he also




164


COLOR-BLINDNESS:


makes some remarks in reference to the loss of the
French steamer "Ville du Havre " by collision
with an English sailing-vessel. This fearful accident most painfully interested us Bostonians, since
so many were lost from our midst in that ill-fated
vessel. I have frequently expressed in private
my own suspicions that the accident may have
been caused by color-blindness; but I will here
simply quote Dr. Favre:"After the loss of the 'Ville du Havre,' the newspapers
which described the collision stated most positively that the
green light was not recognized in time. If the steamer's
officers and crew, who should have seen the signal-light,
were never tested for color-blindness, there is one chance in
twenty that the officer or sailor whose duty it was could
not distinguish green, and one in seventy-five that he would
confound this color with red. We know how the matter
ended. The English admiralty decided that the English
vessel was free from all blame, and the French admiralty
declared that the French vessel could not be in any way
criminated. No one thought of attributing the mistake to
the very probable one of color-blindness."
I lately had curious proof of the color-blindness
of a sea-captain, who, I understand, has now retired
from active service. He was in the habit of working worsteds to while away the monotony of a seavoyage. These worsteds, however, always had to
be picked out for him, and the colors marked, to
avoid his making mistakes.
Dr. Daae of KragerU, Norway, in a lecture on
color-blindness, given April 10, 1878, before the
Medical Society of Christiana, says, -
" We must admit that the possibility of confounding the
signal-lanterns in general is not so great on the railroads as
on the sea. On the roads the glass of the lanterns, at least
within the limits of each country, has a somewhat definite




ITS DANGERS AND ITS DETECTION.           165
red or green color, which even those quite color-blind learn
to distinguish by the difference in the intensity of the light.
The signals, moreover, come at stated times and places,
so that it is known where they are to be expected; and thus
they can be seen and distinguished at leisure, as it were.
Not so on the ocean. In the lanterns of the various vessels
the color of the green or red glass varies considerably. The
green glass varies also more in intensity than tone. Now
let us suppose no signal-light has been seen for some little
time, when suddenly a red or green one appears, and but
one. The question is then, Is this a red or green light?
The vessels are close, and instant decision is necessary. Or
several lights are seen, and the ship we are in is sailing before the wind, and hence bound to keep out of the way.
Most old sailors can remember cases where those on board
were not agreed as to the color of a lantern.
" But how can having rules for the marine of one country
only be of avail? On the ocean vessels from all parts of
the world pass each other. When two vessels meet, it will
help but little if the officers and crew of but one vessel have
normal color-perception.  If there are color-blind on the
other vessel, collision may occur.
" As to the railroads, it is not of such importance that
the requirements as to color-blindness should be the same in
all countries. If one country has one set of regulations, and
another a different one, whilst the third requires no examination, it concerns only the individual country itself. But, as
to the marine, it is necessary to have an international law."
The test for color-blindness now being so simple
as to be readily carried out by the surgeons attached to vessels, especially naval medical officers,
there can be no great difficulty in having an international commission meet, and frame the laws
which shall govern all the navies and merchantmarine of the great maritime nations at least. It
would then be as readily recognized that every
officer and man must be as able to perfectly distinguish the red and green lights as to know where
they belong, and what they mean.




166


COLORl-BLINDNESS:


CHAPTER XVI.
CAN THE RAILROAD AND MARINE SIGNALS BE
CHANGED?
I HAVE given the statistics of the frequency of
color-blindness in Europe from many observers,
and in this country from my own tests. Its frequency, also, among railroad employ&s and sailors
has been proved by European research; unfortunately not yet in the United States. I do not
think any one will now doubt that from two to five
per cent of the men absolutely daily employed on
the railroads in this country are probably colorblind. This granted, we are at once asked, Why
not, then, use some other colors besides red and
green? and, when this is answered, why not use
form instead of color, or the grouping of several
white lights, &c.?
I was long ago convinced theoretically of the
possibility of substituting form for color by day on
the switches, and equally of the impossibility of
substituting any other colors for red and green as
night-signals. Experiment and observation have
now convinced me practically that the railroads
can use form instead of color by day, and can not




ITS DANGERS AND ITS DETECTION.          167
substitute form for color by night. Red and green
are the colors which we must select as being most
in contrast, and also for many practical reasons
in reference to the glass, &c. This I have repeatedly shown at scientific societies.    Experiment
also has proved to me that red and green must be
used as night-signals on the sides of vessels. This
matter is, however, too important for me to simply
give my own unsupported opinion. A color-blind
has gravely discussed with me the necessity of
changing the signals to meet his difficulty, saying,
" It was not right to throw a man out of his employment for a congenital defect, incurable." We
have no better authority than Professor Holmgren,
who explains and discusses this question of other
colors or form, &c., so thoroughly and so practically, that I must quote his remarks verbatim. As
to the modification of the signal system, he says, -
" If congenital color-blindness is incurable, - or at least if
we know no actual remedy for it, -it is necessary to devise
some other method (while retaining the color-blind in the
employment of railways) of guaranteeing the communications against any mistakes they might commit with regard
to signals. It is seen by what precedes that these errors can
and must occur in the use of the signal-colors generally
adopted, -red, green (and yellow). The color-blind has only
two primitive colors; whilst the normal-eyed, according to
the Young-Helmholtz theory, has three. But the usual railroad signal-colors are just those primitive ones which neither
the red nor the green blind can perceive. This choice seems
therefore unfortunate. Wilson is of the same opinion. If
red and green color-blindness are the kinds of complete or
partial blindness which are most generally seen, it would
seem that the difficulty might be considerably diminished,
if, in place of using the actual colors, those should be selected best suited to these kinds of color-blindness, although
they might not suit the third kind of partial color-blindness,




168              COLOR-BLINDNESS:
or violet-blindness, which, according to the experience acquired up to the present time, relatively very seldom occurs.
" Undoubtedly the principle we have endeavored to establish would not be radically enforced; but the practical
result at least would be comparatively nearly accomplished.
As the color-blind has but two principal colors, or two classes
to which he can refer all the colors, it is evident, that, to
select two colors that he can recognize and distinguish without the least hesitation, it would be necessary to select one
from each class. In this way it is always possible to bear
in mind that each kind of color-blindness will always be
able to find two colors distinctly defined, but not more than
two. It is therefore necessary, first, to ask how far two colors
for signals could satisfy the demands of railways and the
navy. As regards railways, it is claimed, and it may be
conceded, that in case of necessity, and perhaps without too
great inconvenience, two colors might be made to answer.
It is certain that three colors are a great improvement upon
two.
" It is scarcely necessary to discuss this point, since it is
only with railroad-signals as with all other signs of communication, -the more numerous they are, the more serviceable
are they, and the more complete can be the communications
they give. The color-sense is the best proof of this; for
certainly the normal-eyed, with three principal colors, has a
more complete and acute impression from the manifold
colors of the external world than the color-blind who has
but two fundamental colors.
" Let us admit, however, that two colors would answer,
and that it were desired to sacrifice the advantage of three
colors for another advantage, -namely, that of retaining in
the service of railways the color-blind: there will still remain the necessity of making a good selection of these two
colors. This is more easily said than done. The choice
must be so made that one color may be selected from each
of the two groups in which all the colors are classed according to the system for the color-blind. Now, it is found,
as we have already seen in the instances of the principal
colors of the red and green blind, that, amongst the seven
colors of the rainbow perceptible to the normal observer, four
- namely, red, orange, yellow, and green - belong to one




ITS DANGERS AND ITS DETECTION.          169
class, and three - especially blue, indigo, and violet- to the
second. Consequently, one of the colors must be red, orange,
yellow, or green; and the other, blue, indigo, or violet. It
should very naturally be our object to give the preference in
the selection to the colors which most strongly affect the eye
at the time of the comparison.  Now, the most intense
colors of the spectrum -that is to say, the most vivid colors
which enter into the white light of the sun -are yellow and
blue, one of each of the two groups. We then select them,
the more willingly that the light of the lantern is, without
any preparation and to a very high degree, yellow, though
it is not homogeneous. But we are far from being so fortunate with regard to blue. We here encounter a difficulty,
ou the contrary, which induces us to doubt whether a change
of colors will accomplish the desired end.
" On all colored surfaces - flags, paintings, semaphores,
&c. -employed by railways to reflect during the day the
sunlight or daylight, the proposed colors answer perfectly
without any doubt, and, in all probability, no color-blind
individual of the kinds specified would nominally make mistakes of judgment. But the night-signals are quite another
matter, and are by far more important for many reasons.
This is, therefore, why we prefer to attach here so much importance to them, as during the day a multitude of different
circumstances might give warning of danger, while during
the night the colored light is the only signal which indicates it.
", The colored lights used for night-signals are made, as
all know, by placing colored glass before the flame of a lantern.  The use of Bengal lights as regular signals could
scarcely be introduced into practice. Now, a colored glass
produces a colored light, because, of all the kinds of light
radiated from the flame, but one kind (or at least mainly
one kind) is allowed to escape, while all the others, or a
greater part of the others, are absorbed by the glass. Thus
blue glass, according to its thickness or degree of coloring,
absorbs all the other kinds of light emitted by the flame of
the lantern, allowing only the blue rays to escape. But,
unfortunately, as is well known by direct experience, the
flame of the lantern emits comparatively but a small amount
of blue light when rape-seed oil and photogene, or generally




170              COLOR-BLINDNESS:
any of our ordinary sources of artificial light, are employed;
and this is why all appear yellow or red when compared with
the light of day. Under such circumstances blue glass can
naturally transmit only a small amount of blue light; and
the light of a blue lantern must, consequently, always be
very feebly luminous.
" Of course the intensity of the light will greatly depend
on the thickness of the glass. But what is gained in intensity by a thin glass is lost in color; for, whilst thin glass increases the intensity, through it will pass, besides the fewer
blue rays, also the red and green. Hence the blue rays become, in an inverse ratio to the thickness of the glass, more
like those from an ordinary lantern, and therefore, to a certain degree, white light. The light is in consequence very
weak, since only enough red and green light passes through
the glass to balance the blue rays.
"What we have just said of blue applies equally to indigo
and violet. The proposed changes of the colors of signals
furnishes, therefore, but two colors in place of three; and
then one is a very feeble light, so that it is difficult to see
it far off when sufficiently colored. This state of things
scarcely holds out much inducement to introduce a reform of this nature. And it seems the more dangerous
that this change of colors in the signals would cause those
with normal sight amongst the personnel to run the same
risk that the really color-blind do: I mean that they would
be forced to distinguish and judge the night-signals alone
by the intensity of the light. The safety of the service, as
we have shown, would gain nothing, and it would be difficult to find a conscientious man desirous of continuing his
work under these circumstances. Such a reform in behalf
of the color-blind would, de facto, shut out a much larger
number of normal-eyed.
" We have heard that blue lights are used on the American roads. This we are not able to deny, but must first be
assured that all the American employes can distinguish the
signals there used, and then learn all the details of the railroad accidents which have happened in that country.
" The result of all that we have just said is, it seems to us,
that the proposed change of the signal colors is not very
practical, and such would be the case with any other choice




ITS DANGERS AND ITS DETECTION.            171
of two colors. It must at least be conceded that the new
signal-colors would be to every normal observer worse than
those now in use with us, as with nearly all nations: in
brief, if they were adopted, it would diminish the public
safety. We must add, that, by adopting them, the principle
we have explained is not taken into consideration, according
to which it is necessary to use a system of signals adapted
to all kinds of color-blindness, since the violet-blind are not
able to distinguish between yellow and blue. The proposed
change should therefore be rejected, it seems to us, on every
practical consideration.
" (2d) Colorless Light and Darkness, Black and White. - It
has been seen that it is impossible to hope for colored signals
suiting every one, color-blind or not. It becomes necessary,
therefore, to try to devise a plan for establishing a system
of signals independent of colors, and based upon the introduction of a colorless light of different degrees of intensity.
We have already discussed the most important of the points
in reference to the intensity of light. While there is nothing more sensible to our sight than the relative intensity of
two lights placed side by side (when the absolute intensity
does not exceed certain limits), in the present case the only
comparison involved is made from memory, so to speak,
which is equivalent almost to an appreciation of the absolute intensity of light. We are so far from being able to
judge of this, that, in spite of a deeply felt need and constant efforts, science even has not succeeded in discovering
suitable measures to apply to it.
"It is, however, necessary to acknowledge here that a system of signals based only on two extremes of intensity of
light-namely, on light and darkness, white and blackought to suit the normal observer as well as the color-blind.
Moreover, such a system ought to satisfy all exigencies, provided it is practically applied, and that two signals only are
sufficient. A white and black flag, &c., would fully suffice
during the day: but such would unfortunately not be the
case at night; for a black light is a contradiction of terms,
and it would be necessary, consequently, according to this
system, for the night, when signals are of the greatest importance, to be limited not to three, but to one signal only, unless
the absence of all signals could be considered as one. Here




172              COLOR-BLINDNESS:
it might be well asked, whether the better system is not that
which is based on the alternations of darkness and light;
that is, movable signals or eclipsed signal-lights. But we
will not enter a field unfamiliar to us. We cannot, however,
but have a sensation of dread at recalling the various artificial means railroad management would have to depend
upon for the purpose of retaining or accepting the colorblind in service. As far as we know, no system has yet
been discovered, based upon the principles alluded to above,
which could advantageously take the place of the one actually in use.
" (3d) Form, Movement, Number. - If we do not succeed in
finding a suitable system of signals, based on the differences
of the quality and quantity of light, there remains but to
appeal to some arrangement in space, if absolutely limited
to the visual sense.
" Of our other senses in reference to recognizing signals, we
might, besides the eye, appeal to the ear. Both can receive
impressions from a great distance. But for our purpose the
ear is still less adapted than the eye; and the former can
only be regarded as secondary for certain definite purposes,
or at short distances. For example: in foggy weather the
whistle and bell are used, &c. Many different ways suggest
themselves of varying the signals by form and arrangement
in space: large brilliant surfaces arranged in different forms;
several small lights grouped in different positions with reference to each other; lights simply disposed, but differing in
value as signals according to their number, or else illuminated figures of simple colors, and produced by different
movements, and so on. A practical difficulty seems to be
connected with such a system: the signals require the illuminated surfaces to be large enough, or placed at distances
considerable enough between the luminous points, to appear
distinctly afar off. Now, the larger such a figure, having the
outlines marked with luminous points, the greater the risk
that a portion of it be hidden by other objects intervening
between it and the eye. These two inconveniences must be
apparent, particularly if these surfaces and illuminated figures have to be placed at every point where colored lanterns
are found; as, for example, on locomotives and cars. Moreover, it will be very difficult to place these signals at all




ITS DANGERS AND ITS DETECTION.            173
points of the road where accidents may happen. These
doubts are perhaps groundless, and possibly better not expressed, as being out of our range.
"It is rather our purpose to discuss this point generally,
and examine it scientifically. We would say, therefore, that
our eye can more readily detect difference in color than
difference in form. The reason of this is very plain. The
retina alone, of all the several parts of the eye, must be
reached by the light, to give us a definite form or definite
light. For the light to reach the retina, all parts of the
eye in front of it must be transparent. When this alone is
the case we can perceive the color of an object or a light;
but if its form is to be appreciated, not only must the light
reach the retina, but it must affect it strongly and definitely
to give us a clear picture of the object. The difference, as
we see, is great. The whole dioptric apparatus of the eye is
necessary for the form of an object to be perceived, whilst
such apparatus is superfluous for simply color-perception.
The greater the number of the active agencies necessary to
accomplish a certain work, the greater the sources of error
in the accomplishment of such work. All organic diseases
of the cornea, the crystalline lens, or the vitreous humor,
hinder the perception of the form of an object, but not of
its color. The advantage as respects color-perception from
this is all the more when we remember that the most finished dioptric apparatus of the eye is relatively imperfect;
and this imperfection is still further increased by many
anomalies. What would a sailor do who had to determine
the form of an illuminated object by the help of a poor spyglass, the glasses of which were dirty, broken, or badly
ground? Probably he could not do it; whereas he could
decide the color of the light in spite of his poor instrument, which would simply reduce the brightness.
"If the system of signals were based upon form, and all
persons discharged from the service of railways, who, in consequence of an imperfection of vision, could not clearly and
decidedly distinguish these signals at a distance, the proportion of such would be larger than that of the color-blind.
To form an idea of the different capacities of the normal eye
in the various senses just mentioned, we will recommend a
very simple experiment. Take something, - colored paper,




174               COLOR-BLINDNESS:
for example; make some plain figures, such as letters, one
of which must be attached vertically to a large black or
white surface. To prevent any distraction from subjective
influences, let some one else select and attach this letter,
while the observer stands at such a distance, that, even with
the eye directed toward it, but a single object can be seen.
If the letters are small, it is not necessary that the distance
should be very great. Then, if the symbol be slowly approached, with the eye fixed on the colored surface, the
following observations in the order in which the different impressions succeed each other will be made: When the letter
is first perceived, neither form nor color can be distinguished.
Nothing is seen but a point or patch darker than the background, if that be white; or lighter, if it be black. The first
attribute remarked, as the distance diminishes, is its color.
When the color is very distinct, it is necessary to approach
considerably nearer before the form is perceptible; that is
to say, before this letter can be read, and its name given.
This simple experiment clearly shows that the eye, as far as
it is possible to compare its capacities in different directions,
is first sensible to the relative intensity of light, then to
color, and finally to form. It would be necessary, of course,
to consider various circumstances relative to the choice of
color, form, &c., if the experiment should be made with exactness to serve as a basis for a scientific demonstration.
What we have said suffices, however, to point out what direction a reform in the signals should take, granting that
any such change is desirable. If a signal system could be
found and practically introduced which depended on light
and dark, then it would be preferable to the present in use.
If such fails, then we must consider the present as the most
practical, because based not only on the principle of the
difference in the quality of light,- that is to say, on color,
-but also because just those colors have been chosen which
practice has proved to be best suited for the purpose. Experience also seems to have decided in favor of this system;
since, in spite of the substitutes proposed with a view to retain the color-blind, it has up to the present time maintained
its ascendency, so to speak, throughout the entire world."
As I have already said, our very practical Ameri



ITS DANGERS AND ITS DETECTION.      175
can people have gradually discarded the use of all
but red and green lights on the railroads, with but
few exceptions. On the sea, of course, the use of
other than red and green signals is impossible.




176


COLOR-BLINDNESS:


CHAPTER XVII.
NECESSITY AND DIFFICULTY OF CONTROL.
ARE there no measures now taken in the United
States to avoid danger from color-blindness? will
here at once be asked of me. I would much like
to have been able to report on the some two hundred railroads of the United States in respect to
any examination of their employes as to colorblindness. It is, however, a delicate question.
From what I have learned, I conclude that here
and there railroad superintendents keep it in mind;
and when, from accident or otherwise, suspicion is
aroused in reference to an employS, the latter is
tested by the superintendent with the flags or lanterns used on the road. This suffices. No medical
man - and much less an expert- is called upon
to decide. If, anywhere in this country, there is
at this time any thing like a systematic test for
color-blindness of the personnel of the road, I shall
be agreeably surprised to learn it. There may be
— but I do not know of any —salaried railroad
surgeons in the United States, whose duty is wholly
with the road, and who could learn to test for
color-blindness. Even when a test of an employ6




ITS DANGERS AND ITS DETECTION.    177
has been reported to me as made, I have had no
proof that it was not simply lack of good eyesight,
and not lack of color-perception. I shall be only
too happy to be corrected by the management if I
am wrong in stating that the railroads of this
country are not more protected from the danger
of color-blindness than were the roads of Europe
before the very recent successful systematic efforts
on the part of those from whom I have quoted in
this volume. I believe practically nothing is at
present sure to protect the community in this
respect.
In the merchant-marine service I very much
doubt if it is any better. I have been told by
naval officers that care is taken in this respect so
far as to look out that the men make no mistakes
as to the port and starboard lights; but I have not
learned that any systematic scientific examination
of the naval personnel is carried out by the surgeons of the navy. I believe I am right in saying
this also of the army. But both army and navy
surgeons are eminently qualified to learn and use
the present methods of testing for color-blindness,
the danger from which they can equally appreciate.
The government can, and no doubt soon will,
carry out proper examinations for color-blindness
in the army and navy. General national laws can
also be enacted as to the merchant-marine; international will come in time as a matter of necessity.
The difficulties with the railroads are, however,
very great. Here the interests and safety of
the community have to contend with ignorance,
prejudice, pecuniary considerations, and incredulity
born of supposed immunity from danger. These




178


COLOR-BLINDNESS:


corporations have no surgeons attached to their
roads, who, in their interests, could carry out proper
examinations to both protect themselves and the
community. Even when interest is awakened
from acknowledged danger justly feared, railroad
managers are very likely to turn to any one calling
himself a medical man, and rely on his statement
as to his ability to examine and pass judgment on
their employds. Then, when they are satisfied
from his reports that they are safe, and accident
happens, color-blindness is proved in the employ6
before the court-and jury, and at once undeserved
miscredit is thrown upon the surety and usefulness of such examinations. It is therefore without hesitation that I would caution as to the choice
of those to be engaged in testing railroad employ6s
for color-blindness. The life-insurance companies
of the country recognize this most thoroughly,
so much so, that examination for life-insurance is
almost a specialty.
We can scarcely hope for such practical good
results as were shown in Sweden, where, by the
simple efforts of one scientific man, all the railroad
employds of the country were in a few months
tested, and laws to govern the future made and
enforced; yet exactly the same is possible in this
country as there. Either the state governments
or the state railroad commissioners can require
thorough examination of all employ6s for colorblindness, or the railroad managers can do it themselves. It is with some natural curiosity that the
solution of the problem will be watched. In one
of these ways this safeguard to travellers must
come, since they will learn the danger they incur




ITS DANGERS AND ITS DETECTION.          179
as quickly as the railroad corporations the danger
they subject them to, not to speak of possible
damages recoverable after an accident due to colorblindness. Not only must railroad employes and
mariners have good eyesight, but they must be
proved to have normal color-perception.
Professor Holmgren is at the head of the control
in Sweden; and his practical knowledge and experience render, of course, all he says of great
value to us about to commence this work here in
the United States. He states as follows:"No half-way measures are allowable. All employes
with defective chromatic vision must be removed from posts
of danger. They should be required to distinguish the signals by their color as the normal-eyed can. The violet-blind
may be allowed on the road. This defect is so rare as to be
scarcely ever met with. There are, of course, positions on
the road not requiring the reading the signals; but it is a
bad plan not to be able to call on any employe in an emergency. Any method of testing for the elimination of the
color-blind will be in place which is tuto cito et jucunde,
the carrying out of which gives the best results in the quickest time, and is open to the smallest amount of difficulties
and misunderstandings. It must not fail to detect a colorblind, or prove that an employ6 is normal-eyed. Whilst
there must be no question of thoroughness, it is to be remembered there are hundreds to be examined, and but little
time can be given to each individual. We cannot have
heavy or costly apparatus to be transported. These points
are to be considered in reference to any method."
" Testing should be only in the hands of those who understand it. On the roads and in the marine the surgeons have
the scientific knowledge necessary to carry out examinations.
On board ship the sailors could be at least roughly tested by
the captain. There are cases where a specialist would need
to be employed to decide whether color-blindness existed or
not, as an ordinary surgeon would shrink from answering
because not in position so to do. So, also, a specialist would
be called upon to decide whether the defect was simulated."




180             COLOR-BLINDNESS:
" There is a difference to be made between those in, and
those seeking, service. The latter we can have time for individually. The former, when a general examination is
undertaken, requires from the numbers great care and decision. A thorough examination would seem to insure safety;
but acquired color-blindness must be remembered. And if,
as is claimed, color-blindness may grow better, it also may
grow worse: hence the necessity of continued vigilance, and
watching for cases from disease or injury, in addition to the
thorough examination for all congenital cases. The possibility of an employe claiming to have been made color-blind
by accident, after having been received into service and
passed his color-test, is a matter also to be thought of.
Color-blindness from railroad injury has been found by Dr.
Favre for instance. The rights and claims of the road, or
rather the public and the individual, are often nicely balanced, and great circumspection is necessary. Severe diseases like typhus, as well as injuries, and also the abuse of
spirit and tobacco, cause color-blindness. Hence, after accidents, the personnel interested should be again tested, and
always any drinking men or heavy smokers quite often
looked after."
" After every railroad accident or collision at sea, dependent in whole or part on misunderstanding colored signals,
not only must the men directly at fault be tested, but also
all those used as witnesses. The necessity of this is selfevident. It would be absurd to punish any one because a
blind man says he saw him break a rule, or let a man go
free because a blind man says he saw him obey the rule.
The same as to color-signals: no witness should be admitted
who is not proved to be free from color-blindness. This is
so plain that discussion of it seems useless; but it is not
recognized by the guardians of the law. The whole question of color-blindness or not, when claimed or denied, must
fall within the province and decision of the specialist
alone."
" Granted now that tests are introduced, and thorough
examinations carried out on our roads, what is to become of
the color-blind? The defect, we know, exists in all degrees
of severity. Whilst there will be no doubt of the necessity
of dismissing the large majority, the decision as to the




ITS DANGERS AND ITS DETECTION.             181
others can be determined by the examiner consulting with
the management, and explaining the character and degree
of the trouble. The possible danger of the incompletely
color-blind being called upon to decide colors quickly, must
never be put out of sight, and this may occur whatever his position
on the road."
" We would again repeat that it is the interest of the management, as well as of the public, to remove absolutely all
difficulties and dangers arising from color-blindness. This
end cannot be considered as attained so long as a single
color-blind employe remains in service. When all colorblind are eliminated is the reform first commenced. It is
no less necessary to carefully test periodically those with
doubtful color-sense allowed to continue in service, to find
if they are better, or worse; and these periodical examinations are necessary as long as any with but imperfect colorsense are retained, and the question remains undecided
whether their defect on the one hand may improve or be
cured, or, on the other, become worse or develop later."
"To settle positively these questions, periodical examinations must be made, 1st, of all with defective color-sense,
once so proved; 2d, of those who have been injured; 3d,
of the whole personnel, in order to detect any who have
become color-blind without perceptible cause. How far
these periodic tests should be carried out depends, of course,
on how thoroughly the original examination has been, and
how strict our laws of rejection have been."
" From what has been said, we see the absolute necessity
of the government and railroad administration being thoroughly acquainted with the color-sense of their, employes,
and the thorough testing and elimination of all color-blind,
as also the preventing the admission of any such hereafter into service. Whatever stand-point is taken, there
rests the very serious importance of the strictest examination of the entire personnel. To carry such out with success,
it is of course, first of all, necessary to have a practical
method of testing that fulfils its purpose in every possible
direction. We lay all the more stress on this point, since
we believe that it has been principally the want of such a
method of testing which has hitherto prevented the reform
desired and urged by us."




182


COLOR-BLINDNESS:


CHAPTER XVIII.
METHODS OF TESTING FOR COLOR-BLINDNESS.
TRUSTING that by this time my readers are
convinced of the necessity of testing all railroad
employds and the marine personnel, we can now
turn to the question of the test itself. On this, of
course, depends our certainty in detecting and eliminating the color-blind. The whole recent widespread control of the chromatic defect on land and
sea in Europe has come undoubtedly from Professor
Holmgren having introduced a test for color-blindness, so simple, so perfect, and so applicable to the
desired purpose, as to render its use imperative,
and its success a matter of necessity. My readers,
I think, will understand the subject better from
hearing what he has to say, as they have already
seen from my numerous quotations from him. As
professor of physiology, and from an extended acquaintance with the color-blind and great experience in testing for the defect, just what he has to
say in his recent work as to methods is here most
valuable. And I introduce it all the more willingly, as my own personal experience as well as
that of many others entirely convinces me of his




ITS DANGERS AND ITS DETECTION.            183
correctness, shrewdness, and practical knowledge.
He says, -
" It has been shown that color-blindness, different as it is
from the normal color-sense, cannot so readily be detected as
might be supposed. We must, in fact, regard it as one of
the peculiarities of the defect, resulting from conditions
already discussed, that it so often escapes detection.
" As the true nature of color-blindness became known, and
the peculiarities of the persons so afflicted recognized, various methods were devised for its diagnosis. There are
already several which vary either in the principle on which
they are based, or in the application of that principle.
These are two important points, and any error affecting
either of them must necessarily lead to a false deduction.
Moreover, if a method fulfils both of these calls upon it,
yet it must also have still other qualities, such as we may
fairly require of any practical means of examination which
is to assist us to our desired end. It must, namely, be
reliable, and of quick and ready application.
"The great majority of people are inclined to believe
that the best method of testing the railroad personnel for
color-blindness would be the use of the signals employed, -
namely, the lanterns and flags, - as being the most direct,
easiest, and suitable. This, to every practical man who has
made no special study of color-blindness, is so obvious as to
be a recognized fact. Any control which we are here concerned with has only the aim of preventing the mistaking
the signals by the responsible personnel. What more simple,
is asked with seeming right, than to be assured that the
railroad employds can distinguish the signals? What other
method can quicker bring us to our desired end? and how
can we reach it more readily, since these signals are in use
on all railroads? At first sight it would seem as if there
was no answer to this, and that we must regard any control
as sufficient which proved that all the personnel could distinguish the colors of the signals. But there is another
condition necessary. The examination must not only prove
that the men are able to distinguish one, two, or any definite
number of lanterns and flags, so or so often, but that they
can distinguish all flags and all lanterns under every condi



184             COLOR-BLINDNESS:
tion; in a word, that their color-sense is as normal as we
have a right to demand. We do not deny that any one
thoroughly familiar with color-blindness and its practical detection may successfully use this method with the lanterns;
but it is tedious, inconvenient, and of itself gives no certain
result. Paradoxical as this may sound, we shall have to confess that such a method is inadmissible, from many wellgrounded reasons. It is therefore our duty to substantiate
this objection, especially as this method seemingly answers
its purpose, whilst in reality it quite defeats it.
"The railroad signal-colors ordered are red and green,
without special nuances of the colors being designated. This
latter, fortunately, is not insisted on, as the railroad managers
could not comply with it, since the colors vary in shade, or
nuance, from many causes. It will be conceded that the personnel must be able to distinguish, not only the most commonly used shades, but they also should be able to clearly
see red and green colors in general. This is not difficult for
the normal-eyed, but simply impossible for the color-blind.
It may be proved by testing the color-blind with selected
lanterns; but even then the method will be found very inconvenient. The color-blind, as has been shown, acquire
from practice a peculiar capacity for distinguishing colored
signals. How and what this is has been explained, and that
their seeing the colored signals is based only on conjecture. Testing, therefore, with lanterns becomes but a hazard
between the examiner and examined, where the latter may
readily often win, and where the former bears all the loss if
the examined afterwards fails but once. Of course the examiner is sure to win if the play is continued long enough;
for, if we know beforehand the examined is color-blind, we
can, sooner or later, cause him to make a mistake as to the
color of the lanterns. But if we do not know that he is
color-blind, and are testing him to decide this, then we shall
soon find how unadapted this method is, and how unpractical.
Naturally much depends upon just how it is employed. For
instance, let us suppose that the usual colored lights are
shown to the examined, one after the other, and he is asked
their color or meaning, whilst from his answer his color-sense
is to be decided on. Now, as we have already shown, the
color-blind may decide rightly; but we need hardly add that




ITS DANGERS AND ITS DETECTION.           185
the normal-eyed may fail from carelessness, inattention, or
even from lapsus lingue. Hence a color-blind is passed as
normal, and the reverse: so in this form the method is not
practical. To attain certainty the test must be continued,
and repeated till the examined's color-sense admits of no
doubt. But how often must we repeat in order to be sure?
How often must mistakes be made to prove color-blindness?
or how often may they be made, and the defect still be considered not present? It is of course impossible to decide
these questions.  Certainty naturally increases with the
number of trials: but the method is still untrustworthy; and
it is depending too much on the knowledge and experience
of the examiner in reference to color-blindness to expect a
decision from him based on such tests. This method of testing with railroad-lanterns takes, of course, even if supposed
sure, a great deal of time, and therefore is inconvenient and
unpractical in the examination of hundreds of persons at
once. The method is also inconvenient as, from the principle it involves, - namely, the detecting the color-sense of the
personnel by the objects their duty requires them to recognize, - the test must be made on the railroad itself. A practical method of testing, however, should be one capable of
being used in any place.
"We have therefore concluded that testing for colorblindness by railroad-lanterns is for many reasons impracticable, and to be discarded. It is worse with the flags:
attempting to use them would cause the examining surgeon
to overlook the majority of color-blind employes. After
what has been said, it is not necessary to discuss this further. We admit, of course, that the method will succeed
better in testing those about to enter the service, and as yet
unfamiliar with the signals: but, if such an examination resulted unfavorably, there would be no just ground to refuse
the applicant if it is believed that color-blindness is curable;
and we do not clearly recognize the distinction between correctly seeing the colors and correctly naming them. We can
give no better advice to those who are not convinced of the
truthfulness of this, than to try it themselves. They will
soon find, that, for testing a person for the first time, lanterns and flags are useless.
"1 We grant, on the other hand, that testing with colored




186              COLOR-BLINDNESS:
lights is quite practicable when we want to examine employes already found somewhat deficient, and desire to
decide whether they can remain in service or not. In this
case it is much better, instead of the usual colored lanterns, to have a large number of colored glasses which
can be placed before the light, or lanterns of varying shades
of color. Then any one who will work methodically will
convince himself and others that the views we have expressed and defended as to color-blindness are correct; and,
as to less faulty chromatic sense, its true effect in recognition of the signals will be duly appreciated. For instance,
persons with feeble color-sense, to distinguish small colored
surfaces, must come much nearer to them than the noimaleyed; whilst those who are completely color-blind cannot
tell the ordinary lights with certainty, even when close to
them. Many color-blind are even unable to say there is a
light, when very feeble, behind a dark-red glass. A very
definite result is obtained by letting two color-blind signal
each other with lanterns I have had specially constructed.
They then make the most marked mistakes. This is a very
good plan to convince a sceptical railroad official, as well as
the color-blind themselves. From the result of our investigations, we deduce the following as applicable to every test
of color-blindness: the examination is not to ascertain the
relation of color-sense to certain signals, whatever these
latter may be, but to decide plainly and surely whether a
given person is color-blind or not, or whether the color-sense
is deficient or normal.
" The test is to find out the character of the color-blindness, not by ascertaining all its peculiarities, but simply one
or more, which quite serves our purpose. This is all needed,
and only exceptional cases require further examination.
Now, there are a number of methods which combine more or
less the essential characters we need in a practical test.
Without discussing them all, we will here notice only a few
points which will enable us to apply some rules to govern
our decision as to which means of examination to employ.
There is hardly any which could not be used, and, if we
could carry it out with the necessary knowledge, would not
serve our purpose as a method of control, at least when
repeated trials could be made. On the other hand, there




ITS DANGERS AND ITS DETECTION.           187
are methods which, used alone, would never, or but seldom,
give us positive results, or which are so tedious and inconvenient as to be quite unpractical. To this class must be
referred all those which, like the test with the lanterns, let
the examined look at various colors or colored objects, and
then demand of them their names.
"This decision is based on what we have already expressed, and also upon our own experience in reference to
the way and manner in which the color-blind learn the
names of colors, and the success practice gives them. But
we do not want to learn the degree of skill a person can attain in naining colors, but how he sees them; in other words,
the character of his color-blindness. The great difference
between these two powers cannot be too well recognized, and
on this ground alone we must again recur to the subject.
Just how a color-blind sees a color it is not possible to
decide; for it is a subjective sensation. On the other hand,
we may form an opinion as to the character of his color-sense
by the confusion or the mistakes which he makes in putting
colors together, which, to the normal-eyed, are essentially
different. Hence any method, to answer all demands upon
it, must be based upon the comparison between different colors, and the confusion the color-blind make in this comparison. An example will render our idea more clear, and show
the importance of it. Suppose, for instance, we have a greenblind. Now, experience shows that such a one confuses
the shades of three colors, which are very different to the
normal eye; namely, purplish red, green, and gray: or he
regards them as exactly similar. Theory shows the reason
of this very clearly. The green-blind has not the receptive
or percipient organ of green. Purple, green, and gray pass
with the green-blind for really one and the same color,
which, however, from what he hears, receives under different
circumstances the separate names. The consequence is, that
he also calls this color sometimes by one and sometimes by
the other name, or always calls it by one and the same
name, -often by the name he first attached to it, or most
often hears. If we test such a person by letting him name
the colors, then, in accordance with the theory, the characteristic signs of green-blindness must in turn, and after many
trials, show themselves. Without guidance from the theory




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COLOR-BLINDNESS:


it is difficult to obtain any clear and correct conception of
the color-sense of a green-blind. If he uses all the three
names, he will often be right, and as often wrong. In the
first case he will readily be thought normal-eyed, and in the
second what Goethe said will certainly occur,-' one gets into
the greatest perplexity, and fairly dreads becoming crazy.'
If the green-blind carefully uses but one of the names, it
will be one of the three, ' purple' (falsely called ' red'),
'green,' or 'gray,; which he applies to all. Suppose now he
uses the name 'green:' then, according to a method depending on the naming of colors, we should conclude that he sees
purple and gray badly, but green distinctly. His color-sense
will of course be regarded as abnormal; but no one would
suppose he was green-blind, since he seems to see that color
perfectly. Yet this green-blind will be regarded as such if
he used the term 'red' (purple) or 'gray.' We trust this
example will remove all doubts as to which of the two points
of view is the correct one. Without further defending it, we
hold the fact proved, that any practical method of examination must be based on the principle of comparison."
From what Professor Holmgren has laid down,
we can readily understand why certain methods
are not practical as well as not scientific. These
methods we must therefore briefly criticise before
explaining his. Let us first remember what has
been said as to any method which calls upon the
examined to name colors shown them, - to those
unacquainted with color-blindness, apparently, the
simplest and most suggestive. To all such methods we may apply Professor Helmholtz's criticism:
" As to the examination of the color-blind, simply
asking them to name this or that color will naturally elicit but very little."
Several ways of employing " simultaneous contrast " have been proposed and carried out. Dr.
Stilling of Cassel used colored shadows. If we
hold before a lamp a piece of colored glass, and




ITS DANGERS AND ITS DETECTION.      189
allow the light thus colored to fall upon a white
screen, this will then appear colored. Now, holding a pencil, for instance, before the screen, we
shall have a shadow cast on the colored surface.
This shadow will, to the normal eye, appear of
the complementary color of the glass before the
lamp; whilst to the color-blind the shadow will
appear colorless or black or gray. On this principle is constructed Dr. Cohn's chromasciopticon,
as also the chromatoscope made by Waldstein.
Such tests are not as practical even as they sound,
though Stilling showed how we could get the
colored shadows by daylight. I would refer to
Dr. von Reuss's article in support of my statements.  Holmgren's more practical use of the
shadows I describe below.
Another method of using simultaneous contrast
is based on the experiment of Ragona Scina, and
carried out by Cohn and by Pfliiger. If we bend
a piece of white cardboard to a right angle, and
then fasten to the adjacent surfaces a little piece
of black cloth, we can hold a plate of colored glass,
with one edge resting in the angle of the paper,
about dividing the right angle made by the cardboard: now, looking down from above through
the glass, we see the horizontally placed piece of
black cloth of the color of the glass; but we shall
also see the reflection of the vertically placed piece
of cloth, and this will appear of the complementary color of the glass. These do not, of course,
so appear to the color-blind.
A test, based on H. Meyer's law of simultaneous
contrast, has been proposed by Weber and Pfliiger. This is well given in the English translation




190


COLOR-BLINDNESS:


of "Bezold's Theory of Color," by Mr. Kohler.
Black letters printed on colored paper, when covered with thin tissue paper, show through this of
the complementary color. A gray stripe on a
colored ground, when gazed at, takes the complementary color of the ground.
Any other methods of producing simultaneous
contrast may of course be employed; but they are
useless, as requiring of the examined color-names.
Successive contrast, or complementary afterimages, has been suggested by Schirmer and by
Cohn. If we look steadily a few seconds at a colored surface on a gray ground, and then quickly
remove the colored surface, the ground will appear
of the complementary color. We here again must
depend on what the examined say they see.
A method of testing for color-blindness will at
once suggest itself in the use of the spectroscope.
Hirschberg has recently arranged one in which we
have two spectra, one over the other, but in reversed order. Movable slits allow us to choose
two colors, which appear just alike. The mistakes
of the color-blind in doing this show their defect.
Stilling proposed the use of the spectra of certain
metals, - natrium, lithium, thallium, &c.; and interesting results have been thus obtained.
Rose's color-measurer should be here also mentioned, and Briicke's schistoscope, - only useful,
however, for scientific examinations.
A method of testing has been proposed by Forster's perimeter. This is used by ophthalmic
surgeons in determining loss of chromatic sense
over certain portions of the retina. Small spots
of color are brought up from the circumference




ITS DANGERS AND ITS DETECTION.     191
towards the centre of the field of vision, and we
can thus map out the chromatic visual field.
In 1871 Professor Holmgren directed attention
to what he called the quantitative disturbances of
the color-sense, or incomplete color-blindness.
Professor Donders of Utrecht, in 1875, carried out
this idea in a method of testing which gave us, not
only the fact that the examined was color-blind,
but also in what degree. This is described in a
subsequent chapter as used on the Holland railroads.
Drs. Dor and Favre have modified Donders's
method; and the former published lithographic
plates of the colored disks, of definite sizes, on a
black background. For this there is great difficulty in obtaining the proper printed colors, both
as to uniformity, purity, and saturation.
Suggestions of Professor Holmgren have been
carried out by Dr. Stilling in a method of testing
for color-blindness which has the advantage of not
calling upon the examined to name colors. In accordance with the now well-known laws of colorblindness, letters are printed in colors on a colored
ground: these the color-blind fail to see, as there is
no contrast to them between the letters and the
ground color. Dr. Stilling has, in his more recent
editions of this test, very ingeniously overcome, in
a great degree, certain difficulties; but there are
other practical ones which cannot be overcome.
There is no comparison between it and the scientific simplicity of Holmgren's. It may be used as
an additional method by those thoroughly acquainted with color-blindness theoretically, and practised
in testing for it. Experience has proved this to




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COLOR-BLINDNESS:


those who have attempted to use Stilling's cards
in testing large numbers, and uneducated people.
Mr. J. Clerk Maxwell, in 1855, proposed a method of judging of the chromatic sense by colored
disks revolving on a top. They were so arranged
that the various colors could be combined in any
proportion. We can thus let a person compare
colors, and prove their chromatic defect by their
variation from the normal-eyed. Landolt proposed
a modification for the quantitative determination of
color-blindness. In 1870 Dr. Woinow proposed the
use of a revolving disk, the inner circle of which
was one-half each of black and white, giving us
gray when revolving. Three rings outside of this
were composed of equal parts of two of the three
primary colors, - red, green, violet. To a person
blind to the color not represented in one of the
rings, this ring will appear gray for reasons I have
previously given. Later he modified his disk, as
he accepted four primary colors. The inner ring
is now to be red and violet.(or blue); the outer,
green and violet (or blue); the third is left out.
If the outer appears gray, like the centre, then we
have green-blindness; if the inner, then red-blindness; if both, then red-green-blindness.
More than forty years ago Professor Seebeck
of Germany described his testing a number of
color-blind by methods of comparison of colors.
He used some two hundred pieces of colored
paper, and allowed the examined to sort these,
putting together what looked to them alike. This
was the first time a true method was used; and
he obtained very valuable results, having shown
that there were different kinds of color-blindness,




ITS DANGERS AND ITS DETECTION.          193
and different degrees of each kind, -a most important fact, as I have previously described.
In 1855 Professor Wilson of Edinburgh published the first monograph in book-form on colorblindness. In testing various individuals he used
little bundles of colored worsteds, letting them
sort them out, and put together those seeming
alike. The principle was the same as Seebeck's,
and a true one of comparison, the examined not
being obliged to name any colors. He says, -
"Candidates for appointments where good eyesight is
required are not likely to exaggerate their defects of vision.
Whenever, therefore, any hesitation in distinguishing colors
is manifested, it should be further tried by giving the
party under examination parcels of differently colored cloth,
paper, glass, and the like, and requesting him to assort
them according to their colors. Reds, greens, browns, and
lilacs should form an essential part of these parcels, but not
to the exclusion of other tints and shades. No person
markedly color-blind will, I am persuaded, escape detection
if tried in this way; and the kind and number of mistakes
which he commits will measure the extent of his colorblindness. The mode of examination thus explained is
within the reach of railway superintendents and shipmasters,
and will serve every practical end. But where railway
servants, sailors, soldiers, or others, undergo preliminary
examination by a surgeon, a more minute examination
might be made, and in another way."
He refers to the colored disks, spun on a top, of
Maxwell. I quote from Professor Wilson to show,
first, that, though he used comparison tests, yet
he did not seemingly recognize that such alone
were of value, as proved by what he suggests.
Had the Young-Helmholtz theory of color-perception been then as thoroughly disseminated as now,
he would no doubt have appreciated its value in




194


COLOR-BLINDNESS:


explaining color-blindness. It was not so applied
till 1875 by Professor Holmgren, who at the time
was unaware of Wilson's results.
The Young-Helmholtz theory of color-perception suggested to Professor Holmgren the value
of sorting worsteds in a certain way, based upon
the application of this theory to the vision of the
color-blind. This method of his, and the manner
of using it, I shall give in extenso and in his own
words, and therefore will here only speak of some
other tests which have been copied from it.
Dr. Daae of Krageroi, Norway, has had little
squares of worsted worked on a card in rows.
Some rows are correct; namely, arranged from
the darker to lighter of the same color. Others
are arranged of the colors the color-blind especially
confound; and they will say, when asked, that
these rows are correct. The card is very convenient, not larger than an octavo volume, and
the colors arranged to detect red, green, or violet
blindness.
Dr. Cohn of Breslau proposed working worsted
letters on a ground such as the color of the letter
is usually confounded with by the color-blind.
These are very deceptive to the color-blind, and
they wonder at the normal-eyed's assertion that
there are letters on the worsted surface. But the
deception is only perfect, and the detection sure,
when the color of the letters and the ground-work
are just suited to the especial kind and degree of
color-blindness of the examined. The test as a
modification of Holmgren's has no advantage, and
is not very practical.
Dr. Magnus of Breslau has lately proposed a




ITS DANGERS AND ITS DETECTION.    195
modification of Holmgren's test by letting the examined pick out from bundles of colored worsteds
those which match the colors of the solar spectrum shown them at the same time. This can be
used as an additional method by examiners, but is
not, of course, as convenient and practical as
Holmgren's simple plan.
Professor Donders has recently also proposed
and used an arrangement of worsteds. On a little
disk of wood one of the colors is wound; and the
other, which the color-blind cannot distinguish
from the first, is so wound over it as to form
rays or a star. A large number of these pairs
are chosen, guided by the selection various colorblind make with Holmgren's test; that is, the
two worsteds on the disk are such as the colorblind say look to them quite alike. A color-blind
is therefore detected in not being able to select
those which to the normal-eye present contrasting
colors.
I have thus given Holmgren's discussion of the
principles of a correct, scientific, and sure test for
the detection of color-blindness, and briefly explained what tests have been proposed, because
the whole subject is new to us in the United
States, and the future control of color-blindness,
and assured safety from its dangers thereby acquired, so greatly depend upon the employment
of an absolutely certain method, thoroughly and
understandingly, by competent examiners.




196


COLOR-BLINDNESS:


CHAPTER XIX.
HOLMGREN'S METHOD OF TESTING.- EXAMINATION AND DIAGNOSIS.
JUSTICE to Professor Holmgren demands that I
should here explain what he has done in reference
to these various forms or methods of testing for
color-blindness, and the study of color-sense. He
has been over the whole subject before the recent
observers I have mentioned, who have attached
their names to this or that special modification.
His method of examination with the worstedsto be given in his own words in this chapter -is
therefore to be considered as a natural development of his special studies.
March 31, 1871, he published his views on
"Color-Blindness and the Young-Helmholtz Theory
of Color." 1 He there discussed this theory, and
the methods heretofore used in testing color-blindness. He also gave the explanation of the perimetric examinations afterwards carried out by him.
By experiments with Maxwell's rotating disk he
found the true difference between red and green
1 Om Faixgblindhet och den Young-Helmholtz'ska Fargtheorien, 1871.




ITS DANGERS AND ITS DETECTION.       197
blindness, explaining seven cases of complete colorblindness, —five red and two green. He seems
to have first shown that green-blindness, as a distinct form, in conformity with Young's hypothesis,
did exist, and proved it by exact experiments. In
this, time has shown him to be correct.
Nov. 3,1871, he published "On Forster's Perimeter and the Topography of the Color-Sense."  This
contains a description of the perimetric examinations and the results thereby obtained, especially
the three separate zones of the field of vision of
Woinow, in relation to color-perception.
He used the point of fixation as the centre - the
physiological centre —in contradistinction to the
blind spot, - the pathological centre as he terms it.
He here describes a series of perimetric examinations of the color-blind, beginning with the normal
color-sense, and following up to complete colorblindness. He also first gives here a description
of what he called incomplete or partial color-blindness. This is important to notice, as Stilling
attributes wholly to Donders our knowledge and
understanding of this form of chromatic defect;
whereas Holmgren had very clearly defined it as
a quantitative disturbance of the color-sense.
Incomplete or partial color-blindness, -especially incomplete red-blindness, —he shows, is
characterized by two principal points: First, in
indirect vision with the perimetric examination,
the field of vision differs from that of the complete
color-blind by having a normal central field; but
it is unlike the normal color-sense in having a
much smaller central field, thus in both ways
1 Om FOrsters Perimeter och Fiirgsinnets Topographi, 1871.




198


COLOR-BLINDNESS:


being only a quantitative difference. Second, in
direct vision at the point of fixation, partial colorblindness differs from complete; thus, with good
illumination, sufficiently large colored surfaces can,
at short distances and with careful fixation, be
correctly distinguished in the sense of the normaleyed. It is different from the normal, however,
in that the discernment of colors is uncertain, and
resembles the complete red-blind when the light is
poor, the distance considerable, or the object small,
or when indirect vision is called upon to assist.
Now, these points have been scientifically carried
out and formulated by Professor Donders since
then; but they were understood and described in
principle by Holmgren as early as 1871.
From his perimetric examinations he concluded
that the three color-perceptive elements have from
the centre outwards different extensions, so that
they all three occupy the central field; whilst in
the middle zone only green and violet perceptive
elements exist, and in the outer zone only one of
the latter two. This he thought to be the green,
as most peripheric; but subsequent examinations
proved it to be the violet.
He also in this article expressed the belief that
the property of a specific sensation for green in
any degree is inseparable from the property of the
sensation for red. This afterwards became the
basis of Hering's theory.
Oct. 31, 1873, he published "On Theories of
Color-Blindness." 1 This is a continuation of his
previous work giving his theoretical ideas. It
criticises Fick's theory, and endeavors to reconcile
1 Om Fargblindhetens Theori, Oct. 31, 1873.




ITS DANGERS AND ITS DETECTION.        199
the facts so far established with Young's theory
of color. The difference between Fick's views
and Holmgren's is, that the former refers the material process of color-perception to the peripheric
retinal elements, whilst the latter would equally
divide it between these elements and the central
apparatus in the brain. He also criticises R. Schirmer's article on congenital and acquired anomalies
of color-perception, in which Schirmer gives a
series of pigment colors which have eccentric fields
of vision of varying size. He holds, that, in examining the central as well as the eccentric field
of vision, the proper selection of the grades of
color has been neglected. He gives, therefore, an
idea of those which are equivalent; that is, pigments which, ceteris paribus, correspond to the
same visual fields, and are recognized at the same
distance from the point of fixation.
Holmgren also gives some cases of complete
green-blindness, the characteristics of which are
especially shown in this article. There are, besides, some improved methods of carrying out the
perimetric examinations described.
In 1874 Professor Holmgren published an article
"On the Theory and Diagnosis of Color-Blindness."   This contains the theoretical and practical groundwork for his method of detecting colorblindness, since published and given here in full.
He develops it theoretically from the YoungHelmholtz theory, and practically from Seebeck's
method. He published a plate with colored letters, in this article, on the same principle. He also
1 Om den Medfodda Fargblindhetens Diagnostik och Toori.
Nord. Med. Arldv., B. vi. No. 24-28.




200


COLOR-BLINDNESS:


then warned against the misuse of the table, and
took the same position which he now holds in
reference to all such arrangements of material,
and in defence against imitators. This plate of
colored letters clearly shows it was the basis on
which so much invention has been since made.
He also further discussed the true subjective
color-sense of the color-blind. He proposed means
for rendering the color-perception of the normaleyed like that of the color-blind, so that they
would see colors like the latter. This he accomplished with colored glasses and colored solutions,
as has since been done by Delboeuf, as described in
a previous chapter.
Returning to the two commonest forms, —
namely, red-blindness and green-blindness, - he
gives further proof of the existence of the latter
as a distinct and independent form, analyzing
three additional cases of complete green-blindness.
Finally, he treats the question of the colorvisual field of the color-blind, proving that they
have as many distinct visual fields as primary
colors. He gives in two plates colored perimetric
visual fields of the color-blind.
The method of testing as developed from his
investigations I will now present as originally
given by him. The description may seem unnecessarily extended, and, to the general reader,
quite uninteresting. It is, however, for the benefit
of those who are in the future to examine employ4s in this country. Experience with testing
for color-blindness will prove its value, and the
necessity for its seeming minuteness. Neglect of
its study and directions has given rise to much




ITS DANGERS AND ITS DETECTION.             201
confusion and waste of time on the European
roads, the proof of which will be hereafter given.
PROFESSOR HOLMGREN'S METHOD OF DETECTING COLORBLINDNESS AS DESCRIBED IN HIS ORIGINAL WORK.
"1. -A Short Sketch of the General Principles of the Method.
"Theoretically our method most resembles those of Seebeck and Maxwell, as it is based upon a comparison between
different colors. It therefore first seeks to discover the
chromatic perception of the subject, disregarding the names
he gives to the colors, as generally it is not necessary he
should designate the names. Our method resembles Seebeck's most in this, that it does not require a special apparatus for preparing the necessary tints for the examination:
it assumes there will be a supply of objects of different
colors provided in advance.  It agrees again with this
method in not allowing, as Maxwell's does, the person examined to remain passive, and simply give his opinon of the
resemblance or dissimilarity of the shades indicated, but requires him to discriminate and select the shades, and in
consequence reveal by an act the nature of his chromatic
sense.
" But practically our method differs essentially from Seebeck's. His certainly gives, in a certain sense, more complete results than ours, by requiring the subject to thoroughly classify, in accordance with their reciprocal resemblances and dissimilarites, the various differently colored
objects placed before him. A complete table of his whole
system of colors is the result of this. Our method, on the
contrary, requires the person examined to select, amongst a
large number of variously-colored objects, those alone which
resemble the sample shown him by the examiner. The
difference is evident. Seebeck's method is, without any
doubt, preferable when the nature of the color-blindness in
the aggregate is to be considered; that is, so long as this is
yet unknown. His method then gives a more complete idea
than ours of the nature of the color-blindness. But, for our
actual purpose, the main question is to discover a defect,
with the entire nature of which we are acquainted in ad



202              COLOR-BLINDNESS:
vance. Our practical mission, then, is evidently to discover,
if possible, some certain sign which will enable us to accomplish this end by the shortest possible route.
"If a single proof which would detect the color-blind as
certainly as if he revealed to us his entire system of colors
were discovered, this would undoubtedly be the method preferred to any other, as it would accomplish the object much
more quickly and easily. This is the case with our method.
We are far from denying, in general, the value of a thorough examination; but we will say that it may sometimes be
superfluous. Its practical advantage will not be very great
if at the cost of a great loss of time; and it may even be
prejudicial, if, under a multitude of details, it conceals what
is essential, - in a word, prevents our 'seeing the forest on
account of the trees.' All this may be applied to Seebeck's
method, when the object in view is the one of which we are
in pursuit. Our method again endeavors to seize as rapidly
as possible one or two essential characteristics while neglecting all the others. A single caudal feather of the peacock
reveals whence it came; a single flower or fruit, the plant
whence it was plucked; and the genus man is recognized if
we can but see a face. It is only when the face is mutilated, the flowers, fruits, and caudal feather are defective,
that in certain cases it is necessary to have recourse to other
characteristics.
" Our method rests upon these principles: it also offers
the same security as Seebeck's. But, as regards the time
necessary to accomplish the examination, it bears nearly the
same relation to that of the learned German that a minute
does to an hour. This may seem a very trifling matter at
the first glance, but is in reality of immense practical importance when a multitude of persons are to be successively
examined. A simple calculation shows us in fact that an
examination requiring one day by our method would require two months by Seebeck's.
" It is but just to acknowledge that it was only by weighing the results obtained by Seebeck's method, and following
the Young-Helmholtz theory, as well as the principles we
have indicated as indispensable to a practical method, that
we have succeeded in formulating our own method, such as
we shall explain it in what follows. We also will remark




ITS DANGERS AND ITS DETECTION.            203
that it is very simple, and easily mastered; but we think
this is likewise often the case with all that is useful and
practical, and that simplicity offers great advantages. We
prefer this method because it seems to us more than any
other to fulfil the conditions we have pointed out as necessary to a practical method; namely, certainty, rapidity, and
convenience. The only inconvenience of any moment, besides those it has in common with a greater part of the
others, is, that it requires daylight. It can undoubtedly be
used by artificial light (electrical and calcium lights, and
certain arrangements of lamp-lights with blue glass); but
this causes much loss of time.
" After this rapid sketch of the general principles of the
method, we will proceed to give its details, and shall not
fail to mention generally the reasons why, amongst several
possibilities, we have selected this or that process.
" 2. - The Material and its Arrangement.
"Our method demands neither costly apparatus nor a
special place for the examination. The only necessary
elements are a number of variously colored objects. It consists in taking one from a number of objects promiscuously
thrown together, and asking the person examined to select
from amongst them all the others corresponding with the
first in color. With regard to the colored objects, it of
course matters little in principle what their nature is, as, in
the main, the method never changes, no matter what the
kind selected. But, practically, the choice is by no means
a matter of indifference. Among the ordinary objects suggested, and also used for the purpose, are pieces of colored
paper, glass, or silk, or Berlin worsted, &c., the last of which
seems to us the best, for the following reasons: One of the
chief advantages of Berlin worsted is, that it can be procured in all possible colors corresponding to those of the
spectrum, and each in all its shades from the darkest to the
lightest. Such selections may be found in trade, and are
easily procured when and where desired. It can be used at
once, and without any preparation for the examination, just
as delivered from the factory. A skein of Berlin worsted
is equally colored, not only on one or two sides, but on all,




204              COLOR-BLINDNESS:
and is easily detected in a large pile, even though there be
but one thread of it. Berlin worsted is not too strongly
glaring, and is, moreover, soft and manageable, and can be
handled, packed, and transported as desired, without damage, and is conveniently ready for use whenever needed.
"These advantages are wanting in the other colored objects suggested for use. Colored paper or silk may be used
when light or dark, dull or bright colors are wanted. But
they both have these inconveniences: they must first be cut
into suitable pieces, and they are troublesome to handle.
Moreover, they are easily concealed from view; and it is
necessary to stretch them carefully on a large surface to
enable them to be seen without trouble. They are often
glaring. They reflect, besides their particular kinds of light,
a quantity of white light, which is a prominent defect, as it
misleads the color-blind, who, as we know, judge of colors
by the intensity of light, -that is, the quantity of light; and
he consequently estimates differently the color of a brilliant
surface, according to the position in which it is found with
regard to the eye, &c. The paper is often colored on only
one side, and this gives rise to much trouble, as it is necessary to turn the pieces from one side to the other to see
them in their true colors. Finally, from being so much
handled, the pieces of paper or silk soon become tumbled
and faded.
" Colored glass, which must be in pieces, is not suitable,
from the fact that it is difficult to procure it in sufficiently
great variety. It is, besides, troublesome to transport, easily
broken, and finally inconvenient for using, because necessary to be held against the light of day, or a luminous source,
in order that the color may be seen. The advantage of
being able to use them by any kind of light does not counterbalance their inconveniences.
" Although these are not all the objections, the preceding will suffice to prove the advantages of Berlin worsted.
All this applies equally well to wafers, powders, colored
solutions, spools of colored thread, pieces of wood, and porcelain, especially painted for the purpose, &c. They can all
be, and have been, employed; but none of these objects are,
in every respect, so well suited to our purpose as Berlin
worsted.




ITS DANGERS AND ITS DETECTION.           205
"A selection of Berlin worsted is then made, including
red, orange, yellow, yellow green, pure green, blue' green,
blue, violet, purple, pink, brown, gray, several shades of
each color, and at least five gradations of each tint, from the
deepest to the lightest. Green and gray, several kinds each
of pink, blue, and violet, and the pale-gray shades of brown,
yellow, red, and pink, must especially be well represented.
" The choice of the material does not belong specially to
our method. In fact, Seebeck suggested the use of Berlin
worsted, which was employed by his advice, and still is at
present. To us only belongs the credit of originating the
manner in which it is employed. According to our method,
the examiner selects from the collection of Berlin worsted
in a pile on a convenient table, and lays aside a skein of the
especial color desired for this examination; then he requires
the one examined to select the other skeins most closely
resembling the color of the sample, and to place them by its
side. The chromatic sense of the individual is decided by
the manner in which he performs this task.
" The result of comparison which the examined makesin other words, the little skein of worsted which he selects
and places by the test -shows us in reality what colors seem
alike to him, and thus tells us his relative color-perception.
The rapidity with which this examination is made does not
seem to directly correspond with the nature of the chromatic
sense, but to depend wholly upon the character of the person
examined. One of intelligence, with a quick, practical mind,
is examined in less than a minute. In this time, in fact, a
normal eye could easily find the four or five skeins of the
same color as the sample, and the color-blind make a sufficient number of characteristic mistakes to thoroughly establish the diagnosis.
" It might be supposed that this method could be further
simplified, and time thereby saved, by previously grouping
the colored objects, or, in other words, showing to the examined a number of colored objects arranged in certain system,
and asking of him which look alike, and their names. Here
the worsteds would have no special advantage over other
colored material, and could be replaced by objects with
bright surfaces not necessarily movable. On such a proposed table the various colors may be placed without any




206             COLOR-BLINDNESS:
order, or in a definite order in accordance with their similarity. Thus they may be grouped according to the colorperception of the normal-eyed or the color-blind, and, in the
latter case, in different groups corresponding to the different
forms of color-blindness.
" The grouping of colors which I proposed was on this principle, and it is printed in the 'Nordst Medicinskt Arkiv.,'
1874, and carried out in the plate published with this
book. The plan is a good one where we are dealing with
educated and intelligent people, and many color-blind may
be thereby detected. To be at all complete, and generally
practical, this method must have a much larger number of
shades. Experience shows that the color-blind is often uncertain as to the similarity between two colors, depending
less upon the color than on what to him is the most important distinguishing mark; namely, the intensity of the light,
or the degree of saturation. And, as to equal intensity of
two colors whose similarity he would find, he is so particular,
that the test may be just too much or too little. We must
add that all color-blind of the same class are not as particular
as to intensity of light or degree of saturation; and, moreover,
it is impossible, on plates which are multiplied, to get exactly the necessary colors, whilst the price increases with the
number of colors. The difficulties were therefore enough
for us to abandon this method. The worst is, however, that
the supposed gain in time is more than counterbalanced by
lack of conveniences and other difficulties. In short, the
loss is greater than the gain.
" These remarks hold good, not only in reference to this
form of test proposed by me in 1874, but also to all colored
tables which have so far been published. A proof is, the
worked worsteds of Dr. Daae, and the repeated attempts of
Dr. Stilling to construct colored plates. As is known,
neither have succeeded in solving the difficulties, although
careful and ingenious attempts have been made to conquer
some of those I have spoken of. These tables, from the
very nature of the subject, can only have a limited employment as an additional test, but are for the examination of
masses wholly unserviceable. Experience has perfectly
proved this to me, and will the same to every expert. The
new editions, unfortunately, are not changed in this respect.




ITS DANGERS AND TTS DETECTION.           207
"By such a colored plate, or any similar arrangement
of immovable colored objects, the very work is done which
should have been by the examined; namely, the grouping
of colors seemingly alike. If, however, this is not done,
and the colors are mixed up, then we cannot let them be
grouped in accordance with their similarity. The value of
this method is, that the objects are movable, and can be
mixed and sorted anew.
" Careful consideration will show the importance of this
fact. The object of the test is to ascertain a subjective sensation from an objective expression. Now, man has but one
means of expressing his subjective sensation to another;
namely, by muscular action. The organs of speech and the
limbs are the apparatus of motion best answering this purpose, and most used for it. Of the most movable, the
tongue and hand each is the representative of its group; and
they are the most pliable of all organs. Both equally indicate the different actions by which we impart our thoughts
to others; namely, by words and acts. It is scarcely necessary to indicate, that, as a rule, it is the latter (the hands)
which we rightly have greater confidence in than the spoken
word. This is substantiated in testing the color-blind. We
have seen how readily they are detected when forced to act,
whilst we must equally remember that the names they give
colors are often exactly adapted to conceal their defect. If
it is in his interest, as here is the case, not to expose his
defective perception, but rather to conceal it, he certainly
can do this better by speech than by the hands. This is a
general law applicable here, if the relations between the perception and denomination of an object are recalled as we
have explained them, and the way these two acts are combined in education. On the other hand, it is clear that our
method affords the opportunity, in connection with the investigation of the chromatic sense, of learning much of all the
peculiarities relating to the use of our senses. This is why
we maintain the principle that it is necessary to leave to the
activity of the hands the task of revealing the nature of the
sensations, and to have recourse to the tongue only for verification when there is need of more information.
"The combination of the action of the eye and hands,
which plays in general so important a part in the training




208             COLOR-BLINDNESS:
and use of the senses, is also of great consequence in this
examination. An attentive examiner, especially if he have
already acquired some experience, can draw important conclusions from the manner in which the other executes his
task, not only and directly with regard to the nature of his
chromatic sense, but generally as to his intelligence and
character, and especially in some cases as to his previous
training and exercise in the use of colors, and his skill in
recognizing them. The examination affords us also the
opportunity of making psychological observations, which
contribute, in a great measure, in giving us a clear idea of
the nature of the chromatic sense.
" A practised surgeon can often detect color-blindness by
the first gesture of the examined, and make his diagnosis
before the end of the trial. He can, according to the manner in which the task is performed, form a judgment of a
feeble chromatic sense in instances which are proved correct
by the final result. He also can and must see whether the
result is erroneous simply on account of a misunderstanding
or a want of intelligence, just as he can see whether the
really color-blind succeeds, in a certain degree, from much
previous exercise or a considerable amount of caution. In
short, the method supplies us with all necessary information;
so that, by an examination made with its assistance, a defective chromatic sense, no matter of what kind or in what
degree, cannot escape observation. It also calls upon the
examiner to watch the examined very carefully, and note
his every motion. Different persons act very differently,
and cause the surgeon trouble of more than one kind.
People of medium intelligence, whether they are color-blind
or not, give least trouble, provided they do not feel called
upon to be too shrewd. The examination is most difficult
with people of small intelligence, or of feeble and uncultivated color-perception, or when we have a color-blind
already tested who desires to escape detection, or when the
examined has not had good school-education. Practical
rules for these special cases are given later.
"The principle of our method depends, as we have said,
on the test calling for the selection of but one color among
many. It may be asked what need of such a number of
colors? Would not a smaller answer? We reply that the




ITS DANGERS AND ITS DETECTION.             209
color-blind avoids detection with more difficulty, and the
diagnosis hence is more readily made, the greater the number of the various colors. The normal-eyed readily selects
the right ones from the mass; whilst the color-blind, although the right ones are directly before him, picks out the
wrong ones, thereby disclosing the character of his defect.
Therefore the greater the number of colors the better, of
course, within certain limits.
"What color shall we take for our sample? This is of
importance; for we must of course decide on some one
color. Experience, as well as the Young-Helmholtz theory,
teaches us that more than one color may serve as the sample
in searching for a sure and definite characteristic of defective chromatic sensation. All colors do not, however, meet
this equally well: hence it is worth while to establish certain rules as to a correct choice.
" The faculty possessed by the eye of distinguishing colors,
and that of defining the degrees of light and color (of
"saturation") are relatively very different; but these special faculties have this in common, that they have their
maximum activity in a certain intermediary region of absolute intensity of light, and their minimum at the two limits
of this region. Just as we experience the most difficulty in
distinguishing between the shades of intensity of light by
a very feeble or very strong illumination, so it is difficult for
us to distinguish colors slightly or strongly luminous, or the
deepest and the lightest. It is therefore necessary to select
as a suitable color for discovering a feeble chromatic sense
either the lightest or darkest shades. The well-defined
kinds and degrees of a defective chromatic sense confound
only colors of mean intensity. But in this case, also, it is a
question what tones of color to choose. For my choice I
have been guided by the Young-Helmholtz theory, and for
the reason that I have proposed my method in support and
proof of that theory. As a fact the examination of thousands of persons has convinced me of the excellence of my
choice. I have selected, to determine whether the chromatic sense is or is not defective, a light green (dark green may
be also used), because green, according to the theory, is the
whitest of the colors of the spectrum, and consequently is
most easily confused with gray. For the diagnosis of the




210              COLOR-BLINDNESS:
especial kinds of partial color-blindness, I have selected
purple (pink); that is, the whole group of colors in which
red (orange) and violet (blue) are combined in nearly equal
proportions, at least in such proportions that no one sufficiently preponderates over the others, to the normal sense,
so as to give its name to the combination. This is the
reason for this choice. Purple occupies a singular position
amongst colors: although a mixed, it is, we know a color
as well "saturated" as the colors of the spectrum, and
might be, from this point of view, classed with them,
although it is not found in the spectrum. In fact, it has
been regarded as the eighth color of the spectrum, closing
the circle of saturated colors. Purple is of especial importance in the examination of the color-blind, for the reason
that it forms a combination of two fundamental colorsthe two extreme colors- which are never confounded with
each other. In fact, from a color-blind point of view, one
of two things must happen, according to the theory: either
it excites but one kind of perceptive organs, or it excites
them all. It appears, then, either like a simple color,-that
is to say, like one of the two colors of the combination,- or
like white (gray.) Experiment has confirmed this hypothesis. Our sample colors, therefore, are the two complementary colors of each other, - green and purple.
"In the examination of the chromatic sense of a large
number of individuals, it is, of course, of importance to decide quickly, first, whether the chromatic sense of the individual is or is not normal. It is only after establishing the
existence of a defect that its nature or degree must be determined. The sample-colors are therefore employed with
more advantage in a certain order, as the test must be accomplished as a whole, according to a plan that experience
has proved the surest, most rapid, and, finally, most suitable
for the purpose.
"Method of Examination and Diagnosis.
" The Berlin worsteds are placed in a pile on a large plane
surface, and in broad daylight; a skein of the test-color is
taken from the pile, and laid aside far enough from the
others not to be confounded with them during the trial; and
the person examined requested to select the other skeins




ITS DANGERS AND ITS DETECTION.           211
most resembling this in color, and place them by the side of
the sample. In the first place it is necessary that he should
thoroughly understand what is required of him; that is,
that he should search the pile for the skeins making an impression on his chromatic sense independent of any name he
may give the color, similar to that made by the sample.
The examiner should explain that resemblance in every respect is not necessary; that there are no two specimens
exactly alike; that the only question is the resemblance of
the color; and that, consequently, he must endeavor to find
something similar of the same shade, something lighter and
darker of the same color, &c. If the person examined cannot succeed in understanding this by a verbal explanation, we
must resort to action. We must ourselves make the trial by
searching with our own hands for the skeins, thereby showing in a practical manner what is meant by a shade, and then
restoring the whole to the pile, except the sample-skein. As
it would require much time to examine each individual in
this way, it is advisable, when examining a large number at
the same time, to instruct all at once, and, moreover, to ask
them to attentively observe the examination of those preceding them, so as to become more familiar themselves with
the process. By this, time is saved, without loss of security;
for no one with a defective chromatic sense finds the correct
skeins in the pile the more easily from the fact of having a
moment before seen others looking for and arranging them.
He makes the same characteristic mistakes; but the normal
observer, on the other hand, generally accomplishes his task
much better and more quickly after having seen how it must
be done, and this is the advantage of our method.
" The colored plate is for the purpose of assisting the examiner in the choice of his colors, and helping him decide
the character of the trouble from the mistakes the colorblind make. We have attempted to represent the colors we
are now to speak of. They are of two classes, -
"1 st, The colors for samples (test-colors); that is, those
which the surgeon presents to the persons examined; and
"2d, The 'colors of confusion;' that is to say, those which
the color-blind. selects from the heap of worsteds, because he
confuses them with that of the sample.
", The first are horizontal on the plate, and marked with




212             COLOR-BLINDNESS:
Roman numerals; the second are vertical, under the testcolors, and marked with Arabic figures.
"c We have already described why such a table cannot be
constructed with a small number of colors adapted to all
color-blind. It is, moreover, often difficult -even impossible- to accurately give the brilliant colors the worsteds
have. The test-colors, with the exception of II., answer the
purpose; but the others not so well, from the difficulty we
have spoken of, and because all color-blind do not choose
the same shades of the same color.
" The colored table is not intended to be directly used to
test with, though it may serve this purpose occasionally. It
is rather to simply assist the surgeon in his choice of the
correct test-colors, and help him diagnosticate the special
form of color-blindness.
" As to the conformity between the worsteds the colorblind take from the heap and the confusion-colors of the plate,
we must simply rely on the tone, and not much on the intensity of light or degree of saturation. In all cases where
we have to vary from this rule, we must hold to the relative
rather than the absolute saturation. The confusion-colors
of our table are only to illustrate the color-blind's mistakes,
and this purpose they serve perfectly. Having made this
explanation, we will pass directly to the test itself. The
following are the directions for conducting this, and making
our diagnosis from the results: -
" TEST I. - The green sample is presented. This sample
should be the palest shade (the lightest) of very pure green,
which is neither a yellow green nor a blue green to the normal eye, but fairly intermediate between the two, or at least
not verging upon yellowish green.
"Ruile. - The examination must continue until the one
examined has placed near the sample all the other skeins of
the same shade, or else, with these or separately, one or several skeins of the class corresponding to the ' colors of confusion' (1-5), until he has sufficiently proved by his manner
of doing it that he can easily and unerringly distinguish the
confused colors, or until he has given proof of unmistakable
difficulty in accomplishing this task.
"Diagnosis. -He who places beside the sample, one of
the ' colors of confusion' (1-5) - that is to say, finds that it




ITS DANGERS AND TTS DETECTION.            213
resembles the 'test-color'- is color-blind. He who, without
being quite guilty of this confusion, evinces a manifest disposition to do so, has a feeble chromatic sense.
"Remark. - We must remember that we might have
taken more than five colors for' confusion;' but we have
here in view, not every kind of defective color-sense, but only
those important in the business of railways. The number
of colors on the plate is therefore slifficient, as these are the
most important and most common.
"As to No. 1, which represents the gray color, we would
remark that too much stress must not be laid on the
light intensity, or on slight differences in the color-tone.
This is especially true of the gray skeins which the examined puts with the sample. If we need determine only
whether a person was color-blind or not, no further test
would be necessary. If we want to know the kind and
degree of his color-blindness, then we must go on with
another test.
" TEST II. - A purple skein is shown the examined.
The color should be midway between the lightest and darkest. It will only approach that given in II. of the plate,
because the color of the worsted is much more brilliant and
saturated, and more towards the blue.
"Rule. -The trial must be continued until the one examined has placed near the sample all or the greater part of
the skeins of the same shade, or else, simultaneously or separately, one or several skeins of 'confusion' (6-9). He who
confuses the colors selects either the light or deep shades of
blue and violet, especially the deep (6 and 7), or the light
or deep shades of one kind of green or gray inclining to
blue (8 and 9).
" Diagnosis. - 1. He who is color-blind by the first test,
and who, upon the second test, selects only purple skeins, is
incompletely color-blind.
" 2. He who, in the second test, selects with purple only
blue and violet, or one of them, is completely red-blind.
" 3. He who, in the second test, selects with purple only
green and gray, or one of them, is completely green-blind.
" Remark. - The red-blind never selects the colors taken
by the green-blind, and vice versa. Often the green-blind
places a violet or blue skein side of the green, but only the




214             COLOR-BLINDNESS:
brightest shades of these colors. This does not influence
our diagnosis.
" The fact that many green-blind select in this test, besides gray and green or one of these colors, also bright blue,
has led to misunderstanding. Some have from this concluded that red and green blindness may exist together in
the same individual; others have thought that these two
kinds of color-blindness were not readily distinguished by
my method. The former conclusion is not correct. The
two kinds have great similarity in close unanimity with the
theory, but differ in innumerable slight variations. They
are nevertheless, in view of the theory, to be considered as
two sharply defined species.
"The second conclusion can only arise from not understanding and not using the method correctly. The especial
purpose of this method must here be kept constantly in
view, and that is to find a characteristic of the defective
color-perception of the examined. This characteristic, or
sign, with green-blindness, is the confusing the purple with
gray or green, or both. This confusion is the point to be
determined: all else may be neglected. A complete colorblind, who confuses purple with gray or green (bluish green),
or both, is green-blind, do what else he may. This is the rule,
and it will not fail the careful and observant examiner who
understands the application of the test. On the contrary, it
is often possible, in marked cases of incomplete color-blindness, to decide which kind we have by the way the examined
acts with his hands.
"We do not mean by this that the diagnosis is always
very easy. Practice and knowledge are necessary. Moreover, as we have often said, there is a long series of degrees
from incomplete color-blindness to normal vision on the one
side, and, on the other, to complete color-blindness. There
must naturally be a border line where differences of the two
kinds of color-blindness cease to be recognized.
" The examination may end with this test, and the diagnosis be considered as perfectly settled. It is not even necessary, practically, to decide whether the color-blindness is
red or green. But to be more entirely convinced of the
relation of complete color-blindness with the signal-colors,
and especially to convince, if necessary, the railway em



ITS DANGERS AND ITS DETECTION.            215
ploy&s and others who are not specialists, the examination
may be completed by one more trial. The one we are going
to mention is not necessary to the diagnosis, and only serves
to corroborate the investigation.
" TEST III. - The red skein is presented to the subject.
It is necessary to have a vivid red color, like the red flag
used as signals on railways. The color should be that of
II. b of the plate, rather towards yellowish red.
"Rule. - This test, which is applied only to those completely color-blind, should be continued until the person examined has placed beside the specimen all the skeins belonging to this shade or the greater part, or else, separately, one
or several 'colors of confusion' (10-13). The red-blind
then chooses, besides the red, green and brown shades, which,
(10-11), to the normal sense, seem darker than red. On the
other hand, the green-blind selects opposite shades, which
appear lighter than red (12-13).
"Remark.- Every case of complete color-blindness discovered does not always make the precise mistakes we have
just mentioned in the preceding examinations. These exceptions are either instances of persons with a comparatively
inferior degree of complete color-blindness, or of color-blind
persons who have been exercised in the colors of signals,
and who endeavor not to be discovered: they therefore
usually confound at least green and brown; but even this
does not always happen.
" ADDITIONAL NOTE. -We have not given rules for discovering total color-blindness, because' we have not found
any cases of this kind. If any such should be found, they
will be recognized, according to the theory, by a confusion
of every shade having the same intensity of light.
" Violet-blindness will be recognized by a genuine confusion of purple, red, and orange in the second test. The
diagnosis should be made with discrimination. The first
test often shows blue to be a ' color of confusion.' This
may, in certain cases, be the sign of violet-blindness, but not
always. We have not thought it advisable to admit defects
of this kind: only the most marked cases, that other examinations establish as violet color-blindness, should be reckoned in the statistics. Finally, to acquire a desirable uniformity, it is necessary to add, that, in the preparatory




216


COLOR-BLINDNESS:


examination, it is my habit to indicate in the journal, especially kept for that purpose, cases of complete color-blindness
by 2 (2 R., 2 G., 2 V.), those of incomplete blindness by 1,
and those of feeble chromatic sense by 0.5 (0.5 R., 0.5 G.,
0.5 V.)."
Professor Holmgren has subsequently published
a further explanation of this method of testing
for color-blindness, which is not in the Swedish,
French, or German edition of his book, nor in the
abridged translation of the Smithsonian. I therefore add it here in full, as it is very important for
examiners:
"The Detection of Color-Blindness among Large Numbers.
"Those who, in the collection of material for scientific
research or for the practical purpose of control among railroad employes and sailors, have to test the color-sense of
large numbers of persons, in order to separate the color-blind
from the normal, and ascertain the former's kind of defect,
will have found the great value of a method which is rapid
and sure in its working. This is very satisfactorily fulfilled
by my method with the worsteds as originally given. But,
to gain still further time, -that is, to increase the rapidity
of the examination without detracting from its surety and
practicability, -I have lately somewhat simplified the
method of working, whilst retaining the same principle,
thereby gaining a third or more of the necessary time.
" As my method has been so favorably received, and its
use spread so rapidly and so widely, I think it right to give
a brief explanation of this modification for the benefit of
professional men.
"The worsted method, from the many colors and the
movable character of the material, is very readily applicable to any special case. It can, as no other, be variously
modified to meet circumstances. We are here dealing with
practical contrivances of more general value, which, simple
as they may seem, were only learned by long experience.
They partly relate to the worsteds, and partly to the particular way of carrying out the test itself.




ITS DANGERS AND ITS DETECTION.            217
" I. The right choice of colors for the collection of worsteds
to be used helps not a little to shorten the examination. All
who are practically acquainted with my method have had
their patience tried by the want of readiness of the normaleyed in picking out the lighter of the green skeins corresponding to the sample from the other green shades of the
bundle. In my book I had to devote many pages to this
point. As I there said, it is the normal-eyed who cause
most loss of time, from their peculiar misappreciation of
the green colors, which is of no importance for the main
object, and generally to be corrected. The color-blind, on
the other hand, make no such errors, but other very different
and characteristic mistakes, and generally very quickly.
" There is therefore considerable gained if we can help
the normal-eyed, and still not change the conditions of the
test for the color-blind. This may be done by leaving out
of the bundle of worsteds all the green colors, except the
lighter ones belonging to Test I. In this primary test the
choice for the normal-eyed will be within quite narrow limits; and, as experience has shown, they are quickly through.
The color-blind, however, to whom the other colors, or socalled confusion-colors, resemble the green, has as great a
choice as before.
"The removal of the superfluous greens is therefore simplifying the method, and an improvement from the saving
of time. We lose also nothing from the certainty of the
color-blind's distinguishing himself from the normal-eyed.
We must, however, not fail to remember, that, though this
renders the method more precise as to the practical point,
yet it also limits it. Opportunity for observing certain
other points is lost. For instance, we have reduced to a
minimum the chance of watching the evident difference in
the intelligence, practice, and education of the examined,
all which possesses a certain psychological interest.
" When, as in railroad employes and sailors, we are concerned alone with rapidly detecting the commonest forms
and degrees of color-blindness,- namely, complete red and
green blindness and incomplete color-blindness, - we may
of course, also, leave out the bright-blue worsteds, and, with
Test II., the bright-violet colors. But in Test II. we must,
for the green-blind, leave all the grades of the bluish-green




218             COLOR-BLINDNESS:
confusion-color, No. 9 of the plate. I will here speak only
of the green colors, because they are of most importance,
and sufficiently indicate the principle of the simplification.
"II. As to the carryi ng-out of the test, it could not be
quicker than the selecting at once from hundreds of persons
the color-blind from the normal-eyed. Such an examination of a mass of people is conceivable, but not practical,
because the necessary surety and certainty, as well as the
classification of the color-blind, demand a separate examination of each individual.
" This simplification, however, allows of a larger number
of persons together being prepared for the test. A principle
of the method is the fact that the examined does not have
to answer any question, but is simply compelled to show
the character of his color-sense by a definite action. This
of course implies his being instructed as to precisely what
he is to do. Just how this is done, and the test conducted,
has no small effect on the rapidity of the whole examination. If each person is thoroughly instructed as to what he
is to do, he finds it extremely simple, and rapidly makes
the test, whether he is color-blind or not.
" The certainty of the test is not interfered with whilst
its rapidity is increased by giving the preparatory instruction to a large number together. It adds to rapidity, if all
the examined, or as many as possible, see each individual
tested. We need not fear that the color-blind can learn
any thing by seeing what the normal-eyed do. The effect
of the examination is all the more striking and convincing
when a number have regularly gone through with the test
correctly, and then one comes who has for some time stood
among the lookers-on, and makes the characteristic mistakes of the color-blind This is always the case. On the
other hand, a normal-eyed may thus learn to imitate the mist
takes of a color-blind. In testing numbers thus, it would,
however, but rarely happen that any one was interested in
simulating color-blindness. Even in this case counterfeiting the color-blind is readily detected by the subsequent
control examination, and hence quite harmless.
" With these preliminary remarks, the practical rules for
quickly testing large numbers for the common forms of
color-blindness may be briefly given as follows: -




ITS DANGERS AND ITS DETECTION.          219
"1st, In the first test, we leave out of the bundle of worsteds all the greens, with the single exception of those to
which the test-color I. belongs (vide the plate), and which
should consist of about five grades or shades.
"' 2d, When using the second test, we put in the bundle or
near it the bluish greens of various intensities, corresponding to the confusion-color No. 9.
" 3d, Before commencing, let some fifty stand round the
table on which the worsteds are placed, or be so arranged
that they can see what takes place on the table. Then call
attention to the test as follows:
"4 4th, We hold up the five green worsteds before the examined, and tell them to carefully observe them, so as to
readily and quickly pick them out from all the mixed-up
colors. Then we place test I., the brightest of the five, to
one side, and mix the others well in the bundle. With our
own hand we rapidly pick these out again, and lay them
with the first to one side: in other words, we perform the
test just as it should be, and this we can repeat as often as
is useful in hastening the examination.
" 5th, After this preparation, we let the examined come
one after the other to the table, and repeat the test they
have seen done. The others must keep quiet, and neither
by laughing, calling out, or signs, interfere with the one
being tested.
" 6th, When any has shown himself color-blind by this
test, then, for the differential diagnosis, Test II. will be used.
Test Il. need not be at all.
" 7th, As in general the test is rapidly made, a feeble sense
of color is shown by great slowness in the manifestation.
" We may thus with perfect certainty test a hundred or
more individuals in an hour, especially soldiers or those
under discipline.
" Finally, I would remark, that, with this method of testing, we need not speak a word, 'of which experience has
convinced me. We may test the dumb without even knowing their sign-language. This method, therefore, recommends itself above all others for testing uncivilized people
whose language is unknown to the examiner. Such examinations, which I have already carried out to a small extent,
will be of interest in reference to the question of development of the color-sense in general."




220           COLOR-BLINDNESS:
I have thus given Holmgren's precise description of the worsted-test as he carries it out. My
own experience has been to lead me to employ the
seemingly longer method with the larger number
of greens. Therefore I add here the exact description given in the original in full of the way
of conducting it. To those of my readers who
may consider it superfluous or unnecessarily extended, I would say, try and go on with the test
alone amongst those with whom a mistake on
your part would be fatal, and you will gladly turn
back and carefully study this following chapter,
with thanks to Holmgren for it.




ITS DANGERS AND ITS DETECTION.


221


CHAPTER XX.
SPECIAL DIRECTIONS FOR CONDUCTING THE TEST.
" THE method, as we have said, plays an important part
in an examination of this kind, not only from the principles
upon which it rests, but also from the manner in which it
is used. The best plan for directing how to proceed is
by oral instructions and de visu; but here we are obliged to
accomplish this by description. Now, this is always defective in some respects, especially if we wish to be brief.
What has been said would evidently suffice for an intelligent and experienced physician; but it may not be superflueus to enter still further into detail to provide against any
possible difficulties and loss of time. The object of the
examination is to discover the nature of a person's chromatic sense. Now, as the fate of the one to be examined
and that of others depend upon the correctness of the judgment pronounced by the examiner, and that this judgment
should be based upon the manner in which the one examined stands the trial, it is of importance that this trial
should be truly what it ought to be, - a trial of the nature of
the chromatic sense, and nothing else, - an end that will be
gained if our directions are strictly followed. It is not only
necessary that the examiner carefully observe them, - which
does not seem to us difficult, - but that he also take care
that the individual examined does thoroughly what is required of him. This is not always as easy as one might
suppose. If it were only required to examine intelligent
people, familiar with practical occupations and especially




222             COLOR-BLINDNESS:
with colors, and with no other interest connected with the
issue of the examination than to know whether they are
color-blind or not, the examination would be uniform and
mechanical; but it is required to examine people of various degrees of culture, all of whom, besides, have a personal interest in the issue of the examination. Different
people act very differently during the examination for many
reasons. Some submit to it without the least suspicion of
their defect; others are convinced that they possess a normal sense. A few only have a consciousness, or at least
some suspicion, of their defect. These last can often be
recognized before the least examination by keeping behind
the others, by attentively following the progress of the trial,
but, if allowed, willingly remaining to the last. Some are
quick; others, slow. The former approach unconcernedly
and boldly; the latter, with over-anxiety and a certain
dread. Some have been perhaps already tested, and practised themselves in preparation for the trial; others have
never been familiar with colors. Among those already
tested may be some color-blind. Some of these latter are
uncertain about their mistakes, and act with great care;
whilst others again are practised in distinguishing the signals and hence conclude that their color-sense is perfect.
They make the trial quickly, and without thought; of course
regularly making the mistakes characteristic of their special form of color-blindness.
" The majority, however, desire to perform their task as
well as possible; that is, to do what the normal-eyed does.
This of course assists in testing them, provided it does not
lead to too great care, as then the testing the color-blind is
more difficult; the trouble being that much time is thus
wasted. Only a very small part have a contrary desire;
namely, to pass for color-blind, though normal-eyed. We
will speak of these later, and now only concern ourselves
with those who stand the test in good faith with the desire
to appear normal, though perhaps color-blind.
" The trial generally goes on rapidly and regularly. We
will only mention those hinderances and peculiarities which
most frequently occur. The examiner must watch that no
mistake is made from not understanding. The names of
the colors need never be used, except to ascertain if the




ITS DANGERS AND ITS DETECTION.             223
name learned hides the subjective color-sensation, or to find
the relation between the name the color-blind employs and
his color-perception.
" The person examined who thinks more of names than
the test itself (this being generally a sign of school-learning) selects not only the worsteds of the same shades, -that
is, those of the same color to his eye,- but all which generally have the name of this color: for instance, in the first
test I., not only the green like the sample, but all that are
green; and with the second test, not only the purple (and
what are generally called red), but all which look reddish,
scarlet, cinnabar, or sealing-wax red. This is of no importance; for those who only do this have scarcely such defective chromatic sense as we are concerned with. He is either
normal-eyed or violet-blind. Simply as a test of violetblindness in the interest of science, we can go on with the
trial, and ascertain how far the grouping of the two colors
was due to a confusion of names or to defective color-perception. Otherwise this examination does not concern the practical point we aim at.
" Under any circumstance it is better to correct the mistakes just mentioned, when arising from misunderstanding,
and even necessary, in reference to mistakes we explained
with the first test. It might be said that it was sufficient
if the examined confounded the sample-color with green
only; that it was indifferent whether he distinguishes carefully between the various kinds of green. But, in fact, this
is not so unimportant. We must give full value to the
determining whether the infraction of the rules arises from
misunderstanding, or lack of practice with colors, or, finally,
from a true chromatic defect. To include all that is green
would render the test tedious and unpractical. In fact, no
little judgment has been exercised in the selection of the
very lightest shade of the green proposed as a sample-color;
for it is exactly what the color-blind most readily confounds
with the colors (1-5) of the plate. If the subject were
allowed to depart from the narrow limits established by the
trial, it would include every shade of green; the result of
which would be that he would prefer to select all the vivid
shades, and thus avoid the dangerous ground where his
defect would certainly be discovered. This is why it is




224             COLOR-BLINDNESS:
necessary to oblige him to keep within certain limits, confining him to pure green specimens, and, for greater security,
to recommend him to select especially the lightest shades;
for, if he keeps to the darker shades, as many try to, he
readily passes to other tones, and loses himself on foreign
ground, to the great loss of time and certainty of the test.
What we have just said of green applies also, of course, to
purple.
" The principle of our method is to force the one examined to reveal himself, by an act of his own, the nature of
his chromatic sense. Now, as this act must be kept within
certain limits, it is evident that the examiner must direct
him to a certain degree. This may present, in certain cases,
some difficulty, as he will not always be guided, and does
either too much or too little. In both cases the examiner
should use his influence, in order to save time and gain
certainty; and this is usually very easily done. This intervention is of course intended to put the examiner in the
true path, and is accomplished in many ways, according to
the case in point.
" We will here mention some of the expedients we have
found useful:
"(A) Interfering when the Examined select too many Colors.
" It is not always easy to confine the one examined within the limits of the method. He easily slips in the first
test, for example, a yellow-green or blue-green skein among
the others, and, as soon as there is one, others follow usually;
and it thus happens that in a few moments he has a whole
handful of yellow-green, a second of blue-green, a third of
both these shades at the same time.  Our process has
assisted us in more than one case of this kind.
"(a) When the person examined has begun to select
shades of one or several other colors than those of the
sample, his ardor is arrested by taking from him the handful of skeins he has collected, and asking him whether his
eye does not tell him there are one or several which do not
match the others, in which case he is solicited to restore
them to the pile. He then generally remarks that there is
some obscuration, and proceeds in one of the following
manners: -




ITS DANGERS AND ITS DETECTION.            225
"1. He rejects, one after the other, the foreign shades;
so that the correct remain, which is often only the sampleskein. Ite is shown what mistake he has made. Names
are used to remind him that one class of green may be
yellow green; and another, blue green: and, to induce him
to avoid them, he is advised only to select skeins of the
same shade as the specimen, although they be lighter or
darker, and have neither more yellow nor blue than that.
If his first error arose only from a misconception or want
of practice in handling colors, he begins generally to understand what he has to do, and to do properly what is required
of him.
"2. Or else he selects and rejects immediately the skein
of the sample itself. This proves that he sees the difference
of color. He is then shown the skein as the only correct
one, and asked to repeat the trial in a more correct manner.
He is again put on the right track as just before; and the
trial proceeds rightly, unless the error arose from a defect in
the chromatic sense. Many seem, however, to experience a
natural difficulty in distinguishing between yellow green
and blue green, or the dull shades of green and blue. This
difficulty is, however, more apparent than real, and is corrected usually by direct comparison. If the method requiring the name of the color to be given is used, a number of
mistakes may be the result. If a skein of light green and
light blue alone are presented to him, asking him to name
them, he will often call blue green, and green blue. But
if, in the first case, a blue skein is immediately shown him,
he corrects his mistake by saying this is blue, and that
green. In the last case it happens so mutatis mutandis.
This is not the place for an explanation. It must suffice to
say that the error is corrected by a direct comparison between the two colors.
"There is, according to the theory, one class of the colorblind - violet-blind - who, in consequence of the nature
of their chromatic sense, and, therefore, notwithstanding
the comparison, cannot distinguish blue and green. But
our method has nothing to do with this class of the colorblind, because such are not dangerous on railways.
" (b) Another Process. -If the one examined place by the
side of the sample a shade, for instance, of yellow green, the




226              COLOR-BLINDNESS:
examiner places near this another shade, in which there is
more yellow, or even a pure yellow, remarking, at the same
time, that, if the first suit, the last must also. The other
usually dissents from this. He is then shown, by selecting
and classing the intermediate shades, that there is a gradation, which will diverge widely if logically carried out as he
has begun. The same course is followed with colors of the
blue shades, if the blue-green were first selected. He sees
the successive gradations, and goes through with this test
perfectly if his chromatic sense is correct.
" To ascertain further whether he notices these additions,
or the tints of yellow and blue in the green, we can take
ourselves the yellow green and blue green to ask him if he
finds this to be so. We can judge by his answer of his
sense with regard to these shades, and the object of this
investigation is accomplished.
" It results from all this that many who are finally considered to have a normal chromatic sense may occasionally
cause embarrassments. In the main, the normal observer
of this kind causes greater loss of time than the color-blind.
It is astonishing to see with what rapidity the color-blind
betray their defect. At least it is found, in the majority of
the cases examined by us, that the first skein of wool selected
from the pile by the color-blind in the first test was one of
the ' colors of confusion.'
"(B) Interfering when the Examined select too few Worsteds.
" Those who evince too great slowness also require the
interferences of the examiner in another manner. We can
lay aside here those cases in which, at the sight of the complex colors of the heap of wool, the examined finds it difficult to select a skein resembling the sample in a collection
where all the particular colors seem to differ from each other,
and in consequence declares immediately that he can find
none resembling the specimen. It is replied that an absolute
resemblance is not demanded, and that no one asks impossibilities; that time is limited, many are waiting, &c. But
there are people who - from natural slowness, from being
unaccustomed to such business, from fear of making mistakes, and especially if previously examined and suspected of
color-blindness, or from many other motives - proceed with




ITS DANGERS AND ITS DETECTION.           227
the greatest caution. They do not even wish to touch the
wool; or they search, select, and replace with the greatest
care all the possible skeins without finding one corresponding with the sample, or that they wish to place beside it.
Here then are two cases: on one hand, too much action with
the fingers, without result; on the other, too little effort.
The examiner is forced to interfere in both cases.
" (a) At the time of a too great manual action, without
corresponding practical result, the examiner must be careful that the eye and hand act simultaneously for the accomplishment of the desired end.
" Some people forget that the hands should be subservient to the eye in this trial, and not act independently. Thus
they are often seen to fix their eyes on one side while their
hands are engaged on the other. This should be corrected,
so as to save time and avoid further labor. When, from the
manual activity of the one examined, or by the unobserved
aid of the examiner, all the correct skeins, or only a portion,
are found in the pile, it is wise to stop, and invite the former
to cross his hands behind his back, to step back a pace, and
quietly consider all the skeins, and, as soon as his eye has
met one of those for which he is looking, to extend his hand
and take it. The best plan is to advise him to look first at
the sample, and then at the pile, and to repeat this manceuvre until his eyes find what he is looking for.
"This stratagem generally succeeds when nervousness
from over-anxiety causes his hands to tremble; but it is
not always easy to induce him to keep his hands behind his
back until the moment for taking the skein in question.
" (b) In cases of great caution, the trial is hastened, if the
examiner come to the assistance of the other by holding
above the pile one skein after the other, and requesting him
to say whether it resembles the color of the sample or not.
It will be advisable first to select the skeins that a colorblind person would approve. If he is so, he will approve of
the selection, and the question is settled; if not, he rejects
them, not without a characteristic smile, or with an expression of wounded dignity. This also enlightens us as to his
chromatic sense. But even the color-blind may, in. such a
case, refuse what is presented, especially if his caution is
premeditated, and he suspects that a snare is intended. It




228              COLOR-BLINDNESS:
is found quite frequently that he rejects the correct shades
likewise presented with the others. This is not the case
when one, having a normal chromatic sense, is slow and
deliberative when subjected to the test under this form. He
has an eye alive to the correct colors.
" One process, in cases of this last kind, is to select false
samples, which are placed quite near the correct one, by the
side, above, or below, to attract the attention of the examined from the right side. It is necessary so to proceed that
the true sample be displaced when the others are drawn out,
so that the person examined may see it move. It does not,
however, always happen to catch his eye. The best means
is then to make him examine the whole, with his hands
behind his back, and invite him to freely make his choice.
But, whatever the process, it is necessary, in every case
where one has been assisted in selecting a certain number
of skeins which he has found analogous to the sample-color,
to make a rule not to conclude the trial without examining
into the effeet of the aid accorded. It is necessary to hold
in the hand the approved package, and ask if he is satisfied,
or if he would desire any change. If he approve the choice,
the diagnosis is established. The same course must be pursued with the defective chromatic sense, that the trial may
be made with or without assistance. To be thorough, the
name given by the color-blind to the colors in question may
be likewise asked.
" In cases where any one suspected of color-blindness has
remained some time to see the trial of others, and where, as
often happens, he has remarked the samples belonging to a
required green shade, he may of course profit by it in his
own trial. But this can be prevented by furtively concealing one or two of these samples. If he seem to be disposed
to confound green and gray, it will be very easy to entrap
him. If we do not succeed, even when assisting him, in
entrapping him in this snare, the hidden samples may be
put back into their places, to be convinced that the trial is
correct.
" From the above, it is seen that many artifices may be
necessary in our examination. It may be regarded as an
advantage of our method that it has at command a great
variety of resources. We have by no means mentioned all;




ITS DANGERS AND ITS DETECTION.           229
and yet many who have only read this description will
probably reproach us with having devoted ourselves too
much to details which seem to them puerile. But we believe that those who have examined the chromatic sense of
a great number of persons, and acquired thereby consideraable experience, will think differently.
" We are convinced that time is saved by such artifices,
and a more certain result obtained; whilst a practised surgeon, who has become to a certain degree a virtuoso, will
accomplish his object quicker and surer by such artifices
than one who neglects them. Recent experience fully confirms this. All those who have familiarized themselves
with my method, and have had experience with color-blindness, and of whose competence there can be no doubt, report,
without exception, that it is to be fully depended on, - the
most practical and the best. Therefore the single unfavorable opinion I know of - namely, that of Dr. Stilling -
can only arise from neglect of the simplest rules of the
method. He thus appears to have wholly overlooked my
first and most important test, and admits his inability to
decide between the names and the color-confusions of the
examined, which is so readily done by my method. Moreover,
he used the plate in my book to test for color-blindness, in
direct opposition to my expressed directions, and the principles of this mode of trial. This will suffice to explain to
every intelligent person Dr. Stilling's erroneous and confused ideas as to the application and carrying-out of my
method. The lack of value of a judgment based upon such
a misapplication and wrong use of the method is self-evident.
"An advantage of our method we showed to be, that
those who were to be examined could be present and see each
individual tested, without this interfering in the least with
the certainty of the result. The individual test is even
hastened thereby. The color-blind, and even the normaleyed who are not familiar with colors, are generally rather
shy about being tested in whatever way it is done. As ours,
however, is carried out, they have more reliance. The majority are even amused. The old adage holds true here, that
it is easier to find fault than to do it yourself. The surgeon,
1 Die Priifung des Farbensinnes biem Eisenbahn und Marinepersonal. Cassel, 1878, lst edition.




230


COLOR-BLINDNESS:


who watches not only the examined, but also those around,
can often see from their faces how closely the latter observe
the person being tested when he takes out the wrong colors,
as also when he neglects the right ones under his eye. This
gives those looking on confidence and assurance, till their
turn comes, when they appear as uncertain as before they
were confident. There is in this something attractive, stimulating the interest, and hence not without benefit.
" From this we see that our judgment of a person's colorsense is made, not only by the material result of the examination, the character of the worsteds selected, but often also
by the way the examined acts during the test. We should
mention a very common manner of persons on trial, which,
in many cases, is of great diagnostic value. Often, in searching for the right color, they suddenly seize a skein to lay it
with the sample; but then notice it does not correspond,
and put it back in the heap. This is very characteristic;
and, if an examiner has often seen it, he can readily recognize
it, and be assured that it is an expression of difficulty in distinguishing the differences of the colors. We frequently
see this in the first test, with shades of greenish blue and
bluish green. Here it means nothing important: quite
the reverse, however, when it concerns the gray or one of the
confusion-colors 1-5. Uncertainty and hesitation as to
these colors, which the color-blind do not distinguish from
the sample, even when directly comparing them, is positive
proof of mistake, implying defective chromatic vision, like
the complete color-blind. No doubt the form of chromatic
defect which we have called incomplete color-blindness exists
in several kinds and degrees. This is not the place to further
discuss our experience on this point; and, for the practical
purpose we have in view, it is not necessary. As we have
explained, there are, among these, forms gradually approaching normal color-sense. How they appear has been described.
We designated them as feeble color-sense.
"It is, perhaps, not easy to detect this special form by
any other, or even our own, method: therefore we give the
following as a means of so doing. The only way of getting
at the point is one we gave in the early chapters of our book;
namely, the determining at what distance the examined
could distinguish a small colored surface. For, in fact, we




ITS DANGERS AND ITS DETECTION.           231
have to do with a-feeble color-sense, which does not prevent
the distinguishing of the colors, but only renders it difficult.
We may suppose, in comparison to the normal color-sense,
the feeble is due either to a weaker response to excitation
on the part of the color-perceptive organs of the retina, or a
relatively smaller number of these organs. In either case
this method would give us the same result, judging from our
experience in testing the eccentric portions of the field of
vision with the perimeter.
" The method we here speak of shows us also the effect
of habit and practice on the color-perception, and it is worth
while to dwell on this point. It happens not seldom that a
person who by test No. I. has been noted ' incomplete colorblind,' after they know of their mistake and have practised
in distinguishing colors, will so comport themselves at a
second trial that we have to simply mark them as of ' feeble
color-sense.' This fact might support Dr. Favre's idea that
defective chromatic vision may be improved. This possibility, however, does not militate against our hypothesis
from the theory, as to the nature of feeble color-sense. It
does not change our stand-point in the question. We have
the same sometimes with test No. II., explainable by what
we have said; namely, that, between the complete lack of
chromatic sense and the incomplete, there was a series of
gradations, and that just here practice would affect the result of examinations.
" All the examples here spoken of but prove that many
seeming trifles and stratagems are of value in making the
examination, -amongst others the keeping the sample a
little way off from the heap of worsteds, as also the removal
of every thing which can cause the examined doubt and
uncertainty. We must not, therefore, let them do what
many want to; namely, hold a number of the worsteds in
the hand at once. We must make the person being tested
place each skein, as he takes it up, either with the sample
or back on the pile. Many who are not clear whether the
skein is like the sample or not, instinctively put the shades
most resembling the test-sample at the side of the pile
towards it, and thus gradually form a little bridge, whose
security they would not undertake to vouch for. No such
half-rules must, however, be allowed.




232


COLOR-BLINDNESS:


"Deciding whether the Examined are fitted for their Duty.
"The method of scrutiny here described is able to detect,
as we have seen, not only complete or incomplete colorblindness, but a feeble chromatic sense. Moreover, it has
been proved that there is a perfect gradation, from complete
color-blindness on the one side to the normal chromatic perception on the other. The question then naturally arises,
from our practical point of view, whether it is possible to
draw a dividing line between the kinds and degrees of
defective color-vision which would except those who could
not cause any inconvenience to the railway service, and, in
case of an affirmative answer, where such limit is to be
found.
"It must first be remembered, that, in the existing state
of things, these questions neither can nor ought to be settled in the same manner in every case, since the examination is intended for individuals of two different classes,1st, the aspirants for railway employment; and, 2d, the
employds, or those already in service.
"It will be readily understood how great is the difference of the cases, in deciding what may be the result of the
examination. We have already given our views on this
point. Justice here calls for an essential distinction, supposing that the test has been always made with sufficient
accuracy. Hence we must pay especial attention to both
of the above classes when deciding whether an employs is
fitted for his duty.
"(A) Those who are Applicants for Railroad Service.
"rWe must bear in mind that in Sweden, according to
the regulation in force there for the management of state
railways (followed also, as far as we know, on the private
lines), it is required, that, in order to be admitted, each
applicant 'prove by a certificate from a physician that he
is exempt from any kind of infirmity, disease, or defect of
conformation that could be prejudicial to the exercise of his
functions;' and also, that among these defects of conformation, in connection with signals, are reckoned the defects of
the chromatic sense, to which the managers have especially
directed the attention of the physicians attached to the
liues.
-^




ITS DANGERS AND ITS DETECTION.            233
"According to the principles we have stated, the greatest
severity should be observed in this case; or, in other terms,
the least defect in the sense of colors should be a sufficient
ground for rejection.    e
" We must seek, therefore, to adapt the method of test to
this law. The object of a test is to prevent any one from
working as a railroad employd who does not have a perfectly
normal color-perception. We have already sufficiently explained the evils arising from contrary action in case of
admission to railroad-work. The border between normal
and abnormal color-sense, like that between the normal and
abnormal in all analogous fields, is purely conventional, and
can never be sharply defined. In this case, however, it is
necessary, and our experience shows, that, so long as the
question of improving color-blindness is an open one, we
must consider as over the border the slightest chromatic
defect that our method can detect, or the slightest degree of
incomplete color-blindness; that is, feeble color-perception.
In consideration of the insignificance of the trouble, our
demand seems hard; and yet we think that it is not too
severe. On the contrary, it is quite possible that hereafter
still stricter rules will become necessary.
" Our practical work is greatly simplified by drawing
this boundary-line. We hold as fixed that the surgeon is
not to be asked to decide whether a man is fit for the service or not, but simply to state the kind and degree of the
color-blindness of the employs referred to him. The decision of an intelligent person is then immediate and
decisive, whether he gives all the examined a written certificate, including the color-blind, or refuses this to the
latter. The statement of the slightest color-blindness in
the first case, as also the refusal to give a certificate in the
latter, are both equal to refusal.
" (B) Employs already in Service.
"We must here ask ourselves if we must not modify
the limit we have just traced, in order to carry out the
principle we stated before; namely, that it is necessary to
adopt less severe rules as to the elimination from the service
of those who are already employed. We here encounter
great difficulties: and it will be seen that it is not possible




234               COLOR-BLINDNESS:
to settle the question summarily; that is, that a sharply
defined limit cannot be traced. In such cases the physician
should always, when he discovers a defect in the chromatic
sense, give a certificate which will indicate its nature.
These indications include, as we have already said, the diagnoses complete red-blindness, complete green-blindness, incomplete color-blindness, or a feeble chromatic sense.
" Our method adheres strictly to the theory; but, on
account of the transition-forms, the diagnosis cannot always
meet the very exact demands of the theory. If we class
with complete color-blindness only those cases in which one
of the three elements of the visual apparatus is wholly
wanting or completely paralyzed, and with incomplete
color-blindness only those cases in which none of the three
are wholly wanting, but simply the receptability of one is
very much reduced, we shall have to group many cases of
the latter class with the first. On the other hand, we shall
often have to consider the lower grades of incomplete colorblindness with feeble chromatic sense. We must, however,
recall cases of a person - especially if subsequently practised - being at the first examination marked as completely color-blind, whilst a second time they appeared only
incompletely color-blind; and others where a person was at
one time incompletely color-blind in the fullest sense of the
word, whilst at another only feeble color-sense could be
shown. In such cases the record should state, in addition,
'incomplete color-blindness,' approaching complete red or
green, or incomplete color-blindness of slight degree, &c.
" The same strict rule should be applied to those already
employed as to those seeking service, and all discharged
who show any lack of color-perception. This would certainly most surely protect the railroad service from danger.
Such a general law, however, has its difficulties, especially
as we must recognize, in respect to the danger of confounding the signals, a great difference between complete colorblindness and a feeble color-perception. The different cases
of incomplete color-blindness vary also in degree. To draw
a line here, and say beforehand who shall be dismissed and
who retained, will be as easy in regard to the first as difficult in reference to the latter; for we are convinced that
every case of complete color-blindness of both kinds, as well




ITS DANGERS AND ITS DETECTION.           285
as every case of incomplete of the higher degrees, should be
immediately dismissed. But, as regards those who may be
retained, it is clear that the first question concerns those
who, at the time of the trial, were regarded in the diagnosis
only as having a feeble chromatic sense, and then those
who in the first test merely confound gray with the samplecolor. But we do not venture to lay this down as a principle; for, if it should be proved that these individuals can
generally distinguish the light of colored lanterns with sufficient accuracy, this does not prove that it is so in every
case, and especially not at every distance required in the
service. This is why we know nothing better to advise than
to refer all such cases to competent specialists, as long as
the transition period of which we have spoken lasts.
"It may be asked, How will the specialists themselves
proceed? To answer this, however, would require a much
more extended scientific discussion of the various methods
than we have proposed here to make. We would only give
some hints. A specialist who is familiar with this subject
has all known methods at his disposition; and, if these fail,
he need but invent others. As, however, I have been in the
position of the specialist in reference to the reform on the
railroads of Sweden, I will here say how I have proceeded.
"In the examination of doubtful cases submitted to my
judgment, I determined according to several of the methods
mentioned in one of the preceding chapters. In general,
these persons were all subjected to a trial according to the
methods of Seebeck and Maxwell, and an examination by
means of the visual perimeter and of colored shadows, as
well as the lanterns of my invention and colored glasses.
These last means have capacity especially in view; and they
are very suitable for the object, when it is desired to investigate those who have been already discovered, by my
method of Berlin worsteds, as having a defective chromatic
sense.
" The light of colored lanterns and illuminated surfaces
generally, conveniently arranged and methodically used,
may serve especially in such cases to enlighten us as to the
faculty of the person examined for appreciating colored signals. Our experiences of this kind have shown us that the
majority of color-blind railway employds, however much




236              COLOR-BLINDNESS:
practice they have had, are utterly incapable of recognizing
and distinguishing the regulation colors of lanterns, especially when they are employed in the shades which are not
most commonly in use in the service. This applies not only
to the completely red and green blind, but also to the incompletely blind. These last require the most circumstantial investigation, and it is not to be assumed that the
lower degrees can stand the trial. They may often, it is
true, distinguish the signal-lights at a short distance with
sufficient accuracy; but they do not succeed at a comparatively greater distance. As the places where the trials are
usually made do not command such distances as railways
for observing signals, signal-lights cannot of course be used
for these trials. They are replaced by small illuminated
surfaces, which, seen from a suitable distance, produce exactly the same effect as lanterns at a great distance. Such
surfaces are made by placing a screen, with a suitable opening covered with a colored glass, before the flame of a lamp.
" We have, however, said enough in reference to means
to be employed in such cases. We had no thought to enter
into the details of them further, and doubt whether this
would on the whole be advisable. The reason of this will
be apparent from the following chapter."




ITS DANGERS AND ITS DETECTION.


237


CHAPTER XXI.
EFFORTS TO CONCEAL OR TO FEIGN COLORBLINDNESS.
"WE have announced that none of the kinds of colorblindness we have in view in this work could escape discovery by our method. But this, of course, assumes that
the subject does his best in the trial, and acts in good faith.
If it happen that one persists, either in concealing a conscious color-blindness or for some other motive, in not
giving the least information by act or word, it is evident
that the examination must fail from this simple reason, and
that it is impossible to draw any positive conclusion with
regard to his chromatic sense. The examiner may in such
a case mention unconditionally in the certificate that the
one examined refused to submit to the usual examination.
"It is not difficult to say how it is necessary to act with
regard to such persons. It should, in fact, be the interest
of each one possessing normal sight, desirous of entering
the service of railways, &c., to endeavor to be competent in
every respect, and consequently to give manifest proof of
his sense of colors. The color-blind alone have any interest in concealing their defect: therefore they endeavor to
escape the trial. Every candidate who will try to avoid the
prescribed trial must therefore be considered and treated as
color-blind. Such obstinacy on the part of an employs
must be considered and treated as an infraction of the regulations.
" But cases may arise also in which those possessing normal
sight will feign color-blindness, and act as if they were so




238


COLOR-BLINDNESS:


affected. This may occur when some one wishes to receive
a pension before the time, or else to escape punishment consequent upon an unexpected accident. These are just the
very cases that put the method and perspicacity of the examiner to the test. The examination then assumes the character
of a kind of criminal inquest, where the judge and the accused
must give all the attention of which they are capable to
their reciprocal acts and expressions, to try to entrap each
other. The one examined tries to prove that he is colorblind, while the examiner endeavors to prove that he has
normal sight. The prospect of coming off victorious in so
singular a contest rests, in the last resort, with him who best
understands the nature of color-blindness, and has most experience in the manner in which the color-blind act. To
enable the pretender to deceive the examiner, it is absolutely necessary that he surpass the latter in knowledge of
color-blindness. There is in this an element of success to
the examiner, as it would be extremely rare to find a railway
employe or sailor who would, under the circumstances mentioned, be subjected to an examination by a person inferior
to himself in knowledge. It is clear, in fact, that an examination so difficult, so minute, and involving so much responsibility, should be confided to the most competent person
possible. But it is, on the other hand, very improbable that
a case. should occur where it would be necessary that a
learned and experienced specialist would have to submit to
an examination.
"In the first place, examinations of this kind must rarely
occur; and, when they do, it must be at least in the most
difficult cases, - that is to say, after an accident, - under
circumstances where the one examined has not had much
time to study his part. It will generally be seen then that
he has not a profound knowledge of the nature of color-blindness, but imagines it to be a difficulty or incapacity to distinguish signal-colors or colors in general. He will therefore be governed by this idea; and either he will perfectly
distinguish every other color, so as to mistake only the
signal-colors, or else he will believe he must confound no
matter what color. But, as we have seen, each kind of
color-blindness follows laws as fixed as the normal sense.
Such a strategem will not fail to violate them, and the individual will be caught in the very act.




ITS DANGERS AND ITS DETECTION.          2?;9
" But there is absolutely nothing which opposes the supposition that this individual may have a certain knowledge
of the nature of color-blindness, or, at least, that he may
have an idea of its regularity with regard to the confusion
of colors. He may have studied the proofs we have cited;
and, owing to the exercise and observation of the colorblind, he will know how to perform them in a manner suitable to the object in view. The examiner has always, however, the choice of other sample-colors; and the Berlinworsted method affords a large choice. If that does not
suffice, and the individual has learned from the truly colorblind to classify the whole collection of worsteds according
to their chromatic sense, - that is to say, that he can stand
the trial according to Seebeck's method, -and if he is so
thorough in his part that there is no means of making him
depart from it by abrupt or contradictory questions, the examiner may employ for the examination a number of other
known methods, but probably unknown to our individual. It
must not be forgotten here that it is generally easier to discover faults committed by others, than to avoid being guilty
of them one's self; and one must be profoundly familiar
with his borrowed part not to be guilty of inconsistencies.
With regard to feigning a certain kind of color-blindness,
we know by our experience, with regard to this, that it is a
very difficult thing, and scarcely ever succeeds before an
attentive and experienced examiner. All these circumstances are advantageous for the examiner; but his superiority is not limited to this. For if it should happen - an
extremely improbable thing-that a pretender were familiar with all the known tests and methods, and besides had
not less practice than talent in executing them as accurately
as the color-blind, the examiner has, nevertheless, the power
of inventing, owing to his special knowledge, new tests, and
of varying those already known.
" When speaking of the examination of those already in
service, and the rules to govern us here, we called attention
to the necessity of acting with great caution in doubtful
cases. The test for color-blindness should then be carried
out by a competent specialist; but the details of the several
methods he would use we purposely omitted. Still less do
we think it well to give details in reference to the trial of




240             COLOR-BLINDNESS:
those simulating color-blindness. It rarely happens that a
writer or professor has cause to withhold the very fullest
knowledge of any special department of knowledge. Our
case is, however, an exception; for every further detail is
but putting another weapon in the hands of the malingerer,
and thereby contributing to diminish the chances of success
of the examining surgeon. In such case it is not only wise
but right to keep silence. It may even be doubted whether
too much has not already been said. We thought it, however, proper to say what we have, in order to convince others
that it is very possible to expose a malingerer pretending to
be color-blind. It would be very unfortunate if the author
ities had the slightest doubt on this point. It is not improbable that the facts we have given have caused one or
another to give up the difficult r6le of a pseudo-color-blind.
" Of course such examination requires the greatest care
and foresight, and must be thoroughly and perfectly carried
out before a decision is given. This is justified by the interests at stake. Although such a test should only be put in
the hands of a thoroughly competent person, yet it is but
right that a decision involving so much (fine or imprisonment, perhaps) should not be left to a single individual.
"Besides the precaution, which must not be neglected, of
conducting the examination in the presence of expert and
competent persons, there is an especial means, which, while
being certain of preventing all fraudulent attempts, judges
the accused in the usual manner; that is, by the testimony
of two persons. These two witnesses should be two colorblind of the same kind as that feigned by the examined. If
these two individuals are first subjected separately and independently of each other and the pseudo-color-blind to the
same trial as he, let the results be noted down carefully, and
then the whole three together; and it will then soon be seen
how the case stands with the suspected individual. The
two color-blind will, in this manner, give the necessary testimony without resting upon the discretion of the examiner.
This manner of proceeding must, however, be employed with
caution and discrimination, as the conformity between two
color-blind of the same class is not absolutely perfect in
every respect. The result must therefore always be made
to harmonize by the explanation of the examiner."




ITS DANGERBS AND ITS DETECTION.


241


CHAPTER XXII.
METHOD OF DECIDING THE PRECISE AMOUNT OF
COLOR-BLINDNESS BY HOLMGREN'S CHROMATOSKIAMETER, OR COLOR-SENSE TESTER.-PROFESSOR DONDERS'S METHOD OF DETERMINING
QUANTITATIVELY COLOR-PERCEPTION.
ONE of the additional methods of detecting
color-blindness is of value for examiners to be
acquainted with. It is based on the true principle
of comparison, no names of color being required
of those examined. It also, like the method of
Donders, enables us to express in figures the
amount of the chromatic defect in each individual
case. The apparatus is arranged to enable us to
use colored shadows. It is not very expensive,
and can be used by day or night. To further test
railroad employds or others, after having decided
on their color-blindness by Holmgren's worsteds, it
will be, as I said, of great value to examiners,
and also serve the purpose of physiological experimenters. It has the advantage of giving constant
results independent of the examiner. These
results can be readily understood by the laity,
and the test applied before them. As Professor




242


COLOR-BLINDNESS:


Holmgren says, "the apparatus may also be used
in determining the absorptive power of various
colored glasses," &c. It must be understood that
it is a means or method for the expert alone
to employ. I will here give the author's full description of it. He has tested it thoroughly with
the many color-blind found on the railroads and
elsewhere in Sweden. It is not described in his
book, and first appeared in a pamphlet in Swedish.
The following is from a condensed description in
German, given by Professor Holmgren himself:"I would devote a special chapter to the discussion of the
conditions of colored shadows, and the importance of the light
by which they are produced. I have found it very difficult,
if not impossible, to get a shadow which reflects no light.
Without light the shadow in simultaneous contrast has no
color.
"I hold here also, as always, that every method for the
detection of color-blindness must depend on the principle of
comparison of different colored lights or surfaces. In this
sense the colored shadows can be used as any other colored
surfaces if they are produced by two lights, or, what amounts
to the same, by two from the same source. We may thus
use the light of a single lamp, by letting one portion pass
through the colored glass to the object causing the shadow,
and the screen on which the shadow is cast; whilst another
portion of the light, by means of a mirror near the glass, is
thrown upon the same object. We thus have two shadows
on the screen of complementary color. One is illumined
alone by the light through the colored glass, the other wholly
by the light of the lamp reflected from the mirror; whilst the
rest of the surface of the screen is illuminated by both. Now,
as we move the mirror to or from the lamp, we can regulate
the relative luminosity of the shadows. I have constructed
such an apparatus, which I would call a chromatoskiameter.
In the centre of the apparatus is a petroleum-lamp with a
round wick. The lamp is on a stand, from which project two
horizontal movable arms. On these arms are the rest of the




ITS DANGERS AND ITS DETECTION.            243
apparatus. The colored glass, the pencil to cast the shadow,
and the screen of white porcelaine on which the shadow is
cast are arranged on one of these horizontal arms at a fixed
distance from the flame. On the other arm is the mirror
which can be moved to or from the lamp. The arms are
marked on the sides with a millimetre scale, supposed to
commence in the centre of the flame. Thus the distance of
the several parts from the lamp can be read off on the scale.
" In employing the instrument, I have used a red glass,
which allowed only spectral red to pass, and a green, which
passed mostly the middle spectral green, but also some other
light, - no red, however. In using the instrument to detect
color-blindness, we must grade it by trial, and determine its
constants for the glass used. We must, for this purpose,
find for each glass the distance the mirror must be from the
flame to cause the two shadows to appear alike to the normal eye; that is, of the same degree of brightness each of
its own color. This distance of the mirror for my eye I
found, for the red glass, to be 40 centimeters; for the green,
35 centimetres, - a difference of 5 centimetres. T.o find
this position of the mirror is much easier with the colorblind than the normal-eyed, for the simple reason that
for the former, when the shadows are of the same degree of
brightness, they are generally of the same color. The distance of the mirror for him is quite different from that of
the normal-eyed, and so characteristic as to detect him
thereby. It is also very different in different cases. All
the cases examined can be separated into two distinct series,
corresponding to the two forms of color-blindness I have
described; namely, red-blindness and green-blindness. The
distance of the mirror with red-blindness (the average of
25 cases) was,For the red glass  =   73.2 centimetres
For the green glass =  27.6   s"
Difference (R. G.) = 45.6 centimetres
With green blindness (from an average of 35 cases recorded)
the distance of
The green glass was -  48.5 centimetres
The red glass was  =   28.7    "
Difference (Gr. R.) =  19.8 centimetres




244              COLOR-BLINDNESS:
" Incomplete color-blindness may also readily be detected
by differences of the mirror's distances from that for the
normal eye. For the very slightest grades of chromatic
defect this method is not so good to be used alone, since
such forms of the trouble are apt to be confused with a lack
of knowledge or understanding in reference to appreciating
the relative luminosity of the shadows.
"In the original article the examination of 135 cases
of various grades of color-blindness was recorded. This
method, as is seen, is based wholly on the principle of comparison. It is not, however, the comparison of two colors,
but that of the intensity of two lights of different kinds. It
has this practical advantage, that the color-blind, who are
very sensitive to differences of luminosity, can readily find
the right position of the mirror. Theoretically there is also
the advantage that it shows the chromatic defect to be a
lessened sensitiveness for a special kind of light, - one of
the primary colors.
" In the respective distances of the mirror from the flame,
as read off from the scale, compared with the distance for the
normal eye, we have in every case a relative measure of the
reduced sensitiveness. Now, as the mirror is movable, and
can be altered in position till the luminosity of the two
shadows is alike to the eye of the person examined, the
intensity of the unaltered lamp-light on one shadow will
serve to measure the intensity of the light on the other
shadow, which has passed through the colored glass, and
become more or less homogeneous. As the zero-point of
the scale is in the flame, greater numbers or distances of the
mirror must correspond to lessened sensibility to light of
the color of the glass. This quite agrees with the numbers
above given for red and green blindness; the first showing
abnormal want of sensitiveness for red, and the latter for
green light. This agrees again with the Young-Hemholtz
theory, and also, as well, with the results of my tests with
the worsteds. The cases referred to were first tested with
the worsteds, and the diagnosis confirmed by examination
with the chromatoskiameter.
" The characteristic confusion of colors of the color-blind
does not necessarily imply a great reduction of perception
for any one of the primary colors. They are explainable by




ITS DANGERS AND ITS DETECTION.            245
a disturbance of the color-sense in the individual case,
whereby the sensibility for one of the primary colors, independently of its real value, is reduced in comparison with
sensibility of the other two. This explains a large number
of the cases tested with this instrument.  Hence it is of
value to test each case with two complementary colored
glasses. The difference between the distances of the mirror
for each expresses the value of the defect to be ascertained.
" The absolute distance of the mirror has of course only
a relative value, does not immediately represent the intensity
of the illumination of the shadow; that is, the sensitiveness
of the eye examined. This, however, we can deduce from
a formula I will here give. Taking the above figures as
representing the average distance of the mirror, the sensitiveness of the normal eye (the intensity of the lamp being
unity)
For the red light  - 0.115.
For the green light - 0.137.
The average sensitiveness of the red-blind
For red light = 0.048.
The average sensitiveness of the green-blind
For green light = 0.088.
Or, if we regard the normal color-sense as a measure for
the sensitiveness,
Normal color-sense = 1.00.
Red-blindness    = 0.42 (R.).
Green-blindness  = 0.64 (Gr.).
By the value gained from the distance of the mirror, applied
to normal color-sense, we may calculate the absorptive power
of the glass. The absorption by the glass, expressed as loss
of light, is thus: -
For the red glass  = 42.5 centimetres.
For the green glass = 43.1 centimetres.
"Thus, by using a larger number of suitable colored
glasses, we can study not only the normal chromatic sense,
but also the various forms of color-blindness. The principle of the method does not, however, restrict us in practice
to colored shadows; but it may be extended to any colored




246


COLOR-BLINDNESS:


lights or surfaces. Therefore it would be well, upon the
same principle, to employ the spectral light in the study of
the color-sense and its defects.
" I have here confined myself to the use of two glasses,
principally because these experiments were directed to the
detection of color-blindness among the personnel of the
Swedish railroads, where, of course, we were concerned
with the red and green only. These examinations have at
least proved the existence of green-blindness as an independent typical species, in accordance with the YoungHelmholtz theory, hitherto but little regarded, or ignored.
This is directly opposed to the idea that red and green
blindness are but one and the same thing, called red-greenblindness.
" As to the practical use of this method, I regard it only
as one of the category I have called methods of control, and
in my original article have given the reasons why it is not
comparable with my worsted method as a preliminary test,
which I still regard as the best of any at present proposed."
Another method of quantitative determination
of color-blindness was carried out by Professor
Donders on the Holland railroads. It has not
been given in English, and I present it for the
benefit of our examiners in this country. Like
this one of Holmgren's, it is an additional method.
PROFESSOR DONDERS S METHOD OF QUANTITATIVELY
DETERMINING COLOR-PERCEPTION.
"Approaching slowly a small colored object, the normal
eye detects the color but little later than the light. We
shall not, however, seek long before finding a person who
sees the color much later than he sees the light. On this
is based my method of examination.
" For testing with reflected light, disks of colored paper
are used, 1, 2, 5, or more millimetres in diameter. Each
one is separately glued to a little piece of black velvet;
and, in like manner, pieces from the white, red, and green
signal-flags. These little pieces of velvet, with the colored
disks on them, can with slight pressure be made to adhere




ITS DANGERS AND ITS DETECTION.             247
to a larger piece of velvet a metre square, fastened upon the
wall, and on which one or more can thus be exhibited as
we desire.
l" Color-perception K is in the inverse proportion to the
amount of light; that is, equal to the square of the distance
d, at which the colors are recognized, and inversely proportional to the square of the diameter m. Let D represent
the distance at which the normal eye sees color, of m = 1
(that is, disks of one millimetre diameter), and we have
K     1  '
This formula gives for the normal eye K = 1, and for every
other eye K < 1.
" In the formula of visual acuteness V = -, the distances
are simply d and D (not d2 and D2), because the distinguishing a printed letter is in proportion to the visual angle in
all directions. Moreover, in this formula D is regarded as
constant. This is because, in the varying light of an ordinary room, with fair light, the visual power is near its
maximum. This does not hold in the same degree in reference to distinguishing color. The lack of light is of course
partly compensated for by the greater sensibility of the
retina and the wider pupil; but, with increasing daylight,
the perception of most colors also increases very considerably. Therefore it is important for the examiner to determine each time his own D, and take this into consideration.
In deciding the visual acuteness (form-perception), we take
into account diminished illumination when it materially
reduces our own visual power. This is all the more necessary with color-perception, since the same colors are not to
be obtained exactly alike everywhere; and those obtainable
are not always recognized at the same distance. Moreover,
from use they lose their brightness. We may, however,
accept as a general law, that bright, saturated colors, one
millimetre in diameter, when placed on black velvet in a
good light, will be seen by an eye with normal visual acuteness (ametropia being corrected) at a distance of five
metres.
"This method supposes that the examiner has normal
color-sense, which is readily determined by comparison with
others. It is also necessary that, before testing, both the




248             COLOR-BLINDNESS:
examined and examiner should have been in the room for
a time with equal illumination. Decreasing daylight reduces all colors, but not all equally. Blue, for instance,
requires of all the colors the least light to be recognized
when we pass from a darker to a lighter locality; the most
light, on the other hand, when we go from a lighter to a
darker locality.
"For transmitted light, the flame of a candle may be
used, such as is employed in England to determine the
candle power of gaslight. This is placed behind a blackened wooden screen, in which is an opening, 25 mm. in
diameter, covered with ground glass. In front of this hole
a rotating metal disk is arranged, pierced with holes, 1, 2,
5, 10, and 20 mm. Just behind the opening in the screen
is a rotating disk with holes, - one clear, the others containing red and green signal-lantern glass, as also other colors,
which we can, by turning, bring in front of the hole in the
screen. The candle is arranged to slide along a scale,
thereby giving us its distance from the screen. The red
glass is one that passes mostly red rays, up to orange, but
no others. The green is one which passes a part of the
rays from yellow to bluish green, and a little of the red.
" During the examination, daylight is to be so far excluded from the room as to only render recognition possible
close to. We can then determine the distance A, at which,
for the normal eye for white and colored light, with m = 1,
D = 5 metres. At this distance D in the formula will keep
the nearly constant value of 5 metres.
" With the candle and the finely ground glass employed,
the white candle-light will give us A = 1.75 metres, the
red glass will give us A = 0.65 metres, the green A = 0.25
metres. In this test with transmitted light, care must be
taken to keep the opening in the direction of the candle.
The examination is otherwise conducted in the same way
as with reflected light. If the examined is, color-blind,
then the degree of brightness for the several colors is not
the same in respect to A, and they decide the color from
this difference in the brightness. This is shown if we vary
the value of a, when those who are uncertain call the color
alternately red or green. When using the largest opening,
and bringing the flame close to the glass, there are but few




ITS DANGERS AND ITS DETECTION.           249
persons who fail in recognizing the color if close to. In
this numerical determination to also decide the recognition
with stronger illumination, we need only make our formula
a2
A2, where a is the distance of the flame from the glass
found necessary, and A its normal distance. The power of
color-perception will then be
-    1  d2 a2-     1 d a2
* D2 * A2-m       D * A
1 d    a
Taking /       -=-..1 A=-L, it follows, as L is found by
observation, that the power of color-sense K =L2. It is
more practical to hold to L, and, in general, to remember
L- =  K. With reflected light A is eliminated, and, with
transmitted light generally, a = A; so that, as a rule, we
I d
may confine ourselves to the formula L = *., and, if we
d
use the one millimetre opening, to the formula L = D
"It is interesting to observe how the examined gradually
passes from doubt to certainty. We show him a single test
at five metres' distance. He sees the little disk, but not its
color. A step nearer, and he ventures to call it "red."
Another step, and he doubtfully says, "No, green." Finally,
he says " red " again, and at last decides more positively for
this color. Just where he became certain is readily determined. Or we put a number of the disks of varying diameters together on the large piece of velvet, and, pointing to
each with a stick, ask its color quickly. With partial colorsense it readily appears how, in approaching, first the larger
disks, and then the smaller, are rightly named; whilst with
less color-perception only the larger are told close to, and
where there is complete absence the color of even these is
not recognized.  We may thus determine the numerical
degree of color-blindness with sufficient accuracy.
" The disk must not be steadily gazed at. The examined
must turn his eyes aside, and step nearer, at once giving the
name of the color pointed out. If the answer is not immediate, then again a step, with the eye removed from the




250


COLOR-BLINDNESS:


object, and the question repeated. By steady gazing, the
complementary color may be called up in the eye, and the decision rendered difficult."
In a letter to me of Feb. 23, 1879, Professor
Donders says," I think I may have given too brief a description of my
method. Dr. Daae did not understand that it was not the
preliminary, but only the secondary, examination in which
transmitted light was used, and where the distinction of
colors bad already been proved imperfect. Dr. Stilling
says, that, continuing to fix the eye on the disk, the second.
ary image of complementary color is developed, not aware
that I expressly said that I allow only one or two seconds
for giving the name of the color. Others speak of the great
difference of the daylight, and forget that I prescribe that
every observation is to be made at the same time by the
examined and the examiner, the latter noticing at what
distance (indicated at the point where the examined sets his
foot) he distinguishes the color; and, if this is not five metres,
then it is to be put in the formula as four or three, or whatever distance it is found. The determination or calculation
is not thereby rendered longer or more difficult,"
I considered it proper to introduce here Professor
Donders's replies to the criticisms made on his
method, since, as we see, they arose from a misunderstanding, or neglect of his directions for conducting this quite practical te st, and which was
carried out on the Holland roads, as I have formerly described. I also give the whole explanation of the test, as it is the one required to be used
at present by the five ophthalmic surgeons now
authorized to examine candidates for railroad service in Holland.




ITS DANGERS AND ITS DETECTION.


o261


CHAPTER XXIII.
LAWS OF CONTROL OF COLOR-BLINDNESS NOW
IN FORCE IN EUROPE.-LEGISLATIVE ACTION
OF THE STATE OF MASSACHUSETTS.
HERE in the United States, either the several
State legislatures, the State railroad commissioners, or the individual railroad corporations, will be
sooner or later called upon by the community to
establish and carry out some regulations controlling color-blindness among the employ6s: therefore it becomes of considerable importance for all
parties interested to know how this control has
been effected in Europe, and the precise manner of
conducting the test. In order to answer this, I
have corresponded with many surgeons in Europe,
and, through their instrumentality, am able to here
give the at present provisional laws in reference
to most of the European states.
The European governments have not stopped to
frame laws, but immediately carried out the examinations, and are subsequently considering the precise regulations for the future, &c. It will be also
seen that the governments have provided for the
elimination of all color-blind from their own railroads and navies. The private companies, where




252


COLOR-BLINDNESS:


independent of their government, have followed
its action. In what I have to say as to these laws,
&c., there is much of vital importance for us in
the United States about to commence this control.
I would call the especial attention of my readers
to the prudent and practical action of the Swedish
Government, in comparison with that of the German states, in putting at the head of the control
one who was as competent to conduct it as he was
to originate the method of testing.
Professor Holmgren kindly furnishes me the
following in reference to Sweden: -
CIRCULAR OF THE ROYAL SWEDISH RAILROAD DIRECTORY
TO THE SUPERINTENDENTS.
To the Superintendents.
The royal directory would hereby call the attention of
the respective district-surgeons to the fact that the lack of
power to distinguish the several primary colors excludes
entrance to railroad service: therefore persons seeking
service must be tested for any such lack of visual power.
As it is of importance to be assured that the officials now
in service can distinguish correctly the colors used in signals, the chiefs of sections, by means of the usual flags and
lanterns, or other means they may find best adapted, are to
ascertain if those under them are incapable of recognizing
these colors. The results of such examinations are to be
reported to the directory, and any suggestions in reference
to dismissals which may seem necessary.
Surgical assistance will not be necessary with this lastnamed trial.
C. 0. TROILIUS.
C. LIMNELL.
STOCKHOLM, Sept. 16, 1876.
Professor Holmgren writes me," Having called the directory's attention to the fact that
these rules in reference to those already in service were not




ITS DANGERS AND ITS DETECTION.             253
sufficient, but that a thorough examination by the railroadsurgeons should be made, for which the surgeons must learn
my method, the following circular was issued:CIRCULAR.
To the Superintendents of all the Districts.
The directory hereby orders a surgeon from each district,
next Tuesday the 24th at 12 M., to meet Professor Holmgren
in Upsala, to there learn from him his method of testing for
color-blindness among the employes. Any other of the surgeons of the district may also attend the professor at this
time for the same purpose.
A pass is to be issued both to those surgeons who are
sent to this meeting, and to those who desire to attend, in
accordance with the seventh clause of the travelling regulations.
C. 0. TROILIUS.
C. LIMNELL.
STOCKHOLx, Oct. 16, 1876.
To the Superintendents.
Since, in accordance with the directions of Sept. 16, 1876,
a number of the railroad-surgeons have learned from Professor Holmgren his method of examination for color-blindness, the directory hereby prescribes,
That this examination shall be gradually carried out
among the railroad personnel by the surgeons, in accordance
with Professor Holmgren's method.
That the surgeons who may not have already learned
this method shall instruct themselves, either directly from
Professor Holmgren himself in Upsala, or through those
who attended his lecture on this subject.
That they report to the directory the result of their examinations, together with such suggestions as were required
by the circular of Sept. 16; and, when color-blind are found
in positions where the distinguishing the colors is important,
they are to immediately make the necessary reports and remarks which the circumstances require, without waiting the
termination of the tests.
C. 0. TROILIUS.
C. LIMNELL.
STOCKHOLM, Nov. 9,1876."




254              COLOR-BLI.lDNESS:
The directions of the superintendents to the
surgeons were as follows, for an example:To Railroad-Surgeon Professor C. B. MERTERTON, Upsala.
The following from the di 'ections of the royal railroad
directory is communicated for your information and government: -
That the railroad-surgeors are to test all employes for
color-blindness by Professor ffolmgren's method.
That those surgeons who may not be acquainted with
this method are to at once inform themselves, either from
Professor Holmgren in Up ala, or from some of the surgeons who have heard his e Kplanations and lecture on the
subject.
That a report of these examinations is to be made as
soon as possible.
In reference to the personnel of the traffic-department
now employed, all station-masters have orders to transmit
you lists of the whole personnel under them; and you. are to
record in the proper columns such remarks as the examination calls for.
C. J. HEMMARSKORD.
STOCKHOLM, Superintendent's Office
of the Fifth Traffic District, Nov. 13,1876.
"This is all official which relates to the railroads. It is,
however, seen that all necessary is practically accomplished.
1st, Those entering the service must be tested for colorblindness, and all showing the slightest lack of color-perception refused. 2d, All those now employed are to be
tried, and the color-blind either dismissed, pensioned, or
given employment where the recognition. of the colored
signals is not necessary. I have acted as chief of control,
and tested over again all those who were found defective by
the railroad-surgeons.
" You will thus see we have been very practical. Without first making any laws, we carried out the reform quite
simply under my personal supervision. I still act as the
head of the control of color-blindness; and, now that we
have gained a thorough practical experience, we shall this
year establish laws to govern the railroads and the marine."
(In letter of January, 1879, of Professor Holmgren to me,)




ITS DANGERS AND ITS DETECTION.          255
The Swedish navy and mercantile marine have
not been neglected; and I will here give a transcript from the laws in reference to the former, as
prepared by Professor Holmgreni. In reference to
the mercantile marine, Professor Holmgren writes
me of date March 5, 1879: "I have been unable
as yet to forward you the laws concerning the con
trol of color-blindness in the merchant marine.
The government has not yet given its sanction.
They are thorough, definite, and strict." It must
be remembered that all these laws of Sweden and
the other European countries, as here given, must
be considered as only provisional, and to simply
serve the present purpose of immediately carrying
out the test and the control of color-blindness.
ORDERS IN REFERENCE TO NORMAL COLOR-PERCEPTION
AMONG THE PERSONNEL OF THE IMPERIAL SWEDISH
MARINE AND ARMY CORPS.
1st, Upon his majesty's recommendation, the sect. 54 of
the laws of the Naval School require that every cadet must,
besides other qualifications, possess normal power of vision,
together with normal color-sensation.
[Remark. - This is already so far carried out, that every
cadet, on entering, is tested as to his color-perception. -F.
HOLMGREN, January, 1879.]
2d, In the general orders to the pilot directory it is required, "4That all in the pilot-service, ordinary and extra
officials, shall, as soon as may be determined by the pilot
directory, be examined, to find if they have normal colorperception. Those who do not have the power of distinguishing the colors are to be noted in the list by the pilot
directory. After the examination the number of color-blind
in each district is to be recorded, and sent in to the chief of
the marine department, accompanied by such suggestions
for action as may be considered necessary."
Given at the Palace, Stockholm, Nov. 18, 1876, by imperial order.            FREiEIUER F. WV. vON OTTER,
Marine Minister.




256             COLOR-BLINDNESS:
[Remark. -These examinations have been already carried out, and the results sent in to me. -F. HOLMGREN,
January, 1879.]
3d, The Regulations of the Imperial School of Navigation of.June 1, 1877, Sect. 16, 2.
Every applicant to enter the navigation department of the
school must bring a physician's certificate as to the condition
of his color-perception. A fault in color-perception will not
prevent the reception of the candidate.
[Remark. -This last must be soon stricken out, or altered. -F. HOLMGREN.]
4th, Royal Orders to the Chief of the Military Personnel of
the Imperial Marine.
1st, That all the personnel of the seamen's and boys'
training-ship shall, at the next general review, pass the sur
geon's examination as to their power of color-perception.
Those who fail shall be duly recorded on the crew's manifest,
and a notice of the number of color-blind in each company
be reported by the mustering-officer to the chief of.the marine department.
2d, That all the men of the Imperial Marine Corps, and
bbys of the navy, who have not been examined in accordance
with the 1st regulation, shall be tested under sect. 284 of
the Regulations of the Marine, 3d part, of the required medical supervision. The company report, when the examination was before the man went on board, and the commander,
when this test was after he was on board, shall take note of
the same, to be reported in the former case to the proper military head, who will report to the chief of the marine department; in the latter case, the commander, who will follow the
rules under Rule I., here given.
3d, The special directions in reference to the medical examination, in accepting the recruit, will be given hereafter.
Given at the Palace at Stockholm, Nov. 18, 1876.
FREIHER F. W. VON OTTER.
H. P. LILLIEH6EK.
[Remark. - The examinations ordered in 1 and 2 are long
ago carried out, and the results handed in to me. In reference to No. 3, a committee of military surgeons has, in
connection with the other regulations of acceptance and con



ITS DANGERS AND ITS DETECTION.          257
tinuance, for both the army and navy, formulated the rules
to be followed under No. 3. This has been since published,
and is now only awaiting royal sanction. It is as follows. -
F. HOLMGREN, January, 1879.]
5th. - 1st Part, Sect. 7.
The naval service calls for no especial bodily condition
other than the physical condition required in the line, except the addition of assured normal color-perception. (Vide
the Addendum.)
Addendum. -Special Examination, Sect. 19.
In reference to normal color-sense, care is to be taken
that no one is admitted into the naval service whom the
examination proves to be in any degree red-blind, greenblind, or partially color-blind.
The test for color-perception is to be carried out by Professor Holmgren's method, by which partial color-blindness
is determined from the confusion of the light green, or first
sample, with gray, brownish gray, yellowish green, pale red,
or pale grayish purple (1, 2, 3, 4, or 5).
Red-blindness is determined by confusing, with the purple (II.), blue and violet (6 and 7); green-blindness, by
confusing, with the purple, green and gray (8 and 9). Compare " Color-Blindness in its Relations to Railroads and the
Marine," by Frithiof Holmgren.
Sect. 21. For these examinations, the following apparatus, &c., is necessary, enclosed in a box; viz., a copy o{
the above-mentioned book, and a collection of the worsteds.
The following are in general the regulations of
the Norwegian Government of date May 7,1877:1st, By order of the civil department, all railroad employds are examined by Professor Holmgren's method.
2d, By order of the navy department, the pupils
in the navy-officers' school are to be tested for colorblindness, as also all enrolled in permanent service.
3d, It is now under advisement to require pilots
to be tested for color-blindness; but regulations
are not yet arranged and carried out.




258


COLOR-BLINDNESS:


Several private Swedish steamship companies
have ordered examinations of their crews.
Through the efforts of Dr. Favre, the personnel
of the French Transatlantic Steamship Company
are subjected to a test for color-blindness. The
British Cunard Steamship Company requires the
surgeons of the ships to test the men for colorblindness. Colored glass is provided; but the
special method is left to the individual medical
officer. If, as has been lately stated in print, the
men are subjected only to this test with colored
glass or colored lanterns, we must, from all that
has been shown and proved, consider that there
has been no test as to the true color-sense of the
personnel. Asking the names of colors or of colored lights, &c., will not tell us just how the person examined sees these lights, &c. Steamship
companies, therefore, when they think they have
done all necessary to protect the lives and property intrusted to them, may thus, from want of a
perfect method of testing, be simply gathering into
their crews men whose chromatic defect is most
dangerous, and who could not obtain employment
when a perfect test was applied.
The instructions as to the examination of persons seeking employment in the Bavarian railroad
service are,
I. As to the physical capacity of each individual,
their visual power is to be tested, and also their
color-perception; the result to be recorded in the
report.
II. The test for color-blindness is to be conducted with the accompanying worsteds, which
the applicant is to sort by colors, and designate.




ITS DANGERS AND ITS DETECTION.            259
Only those who can distinguish the differences of
color are to be recorded as free from color-blindness. All other cases are to be noted with the
remark, for example, -" Distinguishes red         (or
green) with difficulty."
The sanitary inspector-general of the railways
of Northern Italy replies,
"' In answer to your question on color-blindness, my reply
is, that although no printed regulation formed by the
administration for our railways exists, which excludes colorblind men from being taken into the service, that contingency is guarded against by instructions given to the sanitary inspectors of the company, commissioned to examine
the candidates for employment on the railways, which are
to this effect: that, as to the visual faculty, they be able
clearly to distinguish the different colors, both by natural
and the artificial light of the lamp used on the trains and in
signal-boxes, at the maximum distance of normal eyesight.
These instructions have been, since the last few years, very
strictly adhered to in the employment of new engine-drivers,
stokers, and signal-men, - in fact, of all who have part of the
great responsibility of the safety of the trains. Owing to
this, and to the fact, that, when the least doubt arises as
to the perfect state of the eyesight of one of our employes
(due to age or sickness), he is at once subjected to a medical examination, we have as yet had to lament no accident
on any of the lines under our direction which could in any
way be attributed to color-blindness."
The minister of public works of Belgium proposed the following questions to the Royal Academy: -
1st, Is color-blindness a congenital defect? and
can it be acquired? In the latter case the administration would periodically test its agents.
2d, What is a practical and efficient method of
determining whether an employ6 fails in chromatic
sense?




260


COLOR-BLINDNESS:


The committee of the academy replies," They are convinced that color-blindness may arise from
a severe disease, contusions or wounds of the head, the abuse
of tobacco and of alcohol. A periodic examination of the
active personnel is therefore advised.... The examination of those suspected of color-blindness should consist in
making them sort, according to their colors, worsteds or silks,
chosen especially for this purpose. The color-blind hesitate
in such a choice as this, and arrange most unexpected
matches. It is the method carried out by Professor Holmgren.... A change or modification of the signal-colors
used has been proposed; but Professor Holmgren has well
answered how impracticable this would be."
I have noticed elsewhere (p. 134) the suggestions
of this committee as to attaching colored glasses,
&c., to the engines, to assist color-blind engineers
or stokers.
Dr. Favre states that the examination for colorperception has been in force on the Lyons railroad
since 1858. In March, 1870, the following special
questions were put to the surgeons of this road: -
1st, How many candidates have you examined?
and in how many years?
2d, Since when have you tested in reference to
colors?
3d, How many color-blind have you found?
4th, What form of color-blindness have you
found most frequent?
5th, Have you observed color-blindness from accident or injury?  How often? How long did it
last? What were the circumstances of the case?
6th, Have you written on the subject of colorblindness, congenital or traumatic?
The reports and statistics thus gathered I have
elsewhere included. In 1876 Dr. Favre reports




ITS DANGERS AND ITS DETECTION.          261
the Dombes et Sud-Est and the Midi roads as carrying out this test.
In 1877 the director-general of the Hollanid railroads called upon Professor Donders of Utrecht
to carry out the examination of the employes for
color-blindness. This was done, and the results
I have already given. Professor Donders drew
up the instructions for the guidance of the twelve
surgeons deputed to carry out the details of the
first examination, and a final official report was
sent in to the director-general.
I have received from Professor Donders the
printed blank required hereafter to be filled out
in the case of every railroad employd.       Every
candidate for service must pass an examination
by one of five ophthalmic surgeons in Amsterdam,
Rotterdam, Anheim, Utrecht, and Leyden. These
surgeons' names and hours for examinations are
printed on the back of the blank, the face of
which reads as follows: -
NETHERLANDS RAILROAD COMPANY. - The undersigned
states that the sight of -   is sufficient (a) for the employment of engineer or fireman; (6) for the employment of
station-master or those who may fill his place, assistants,
haltmaster, director, first conductor, conductor, porter, brakeman, switchman, ranker, bridgekeeper, linekeeper, or linekeeperess.
keeperess.         THE OPHTHALMIC SURGEON.
The               187.
(Signature of the examined to be given in the presence
of the surgeon.)
N.B. -In case the candidate desires employment under
a, b is to be stricken out, and the reverse.
There is required, for a, eyes and eyelids healthy externally, without habitual congestion or inflammation; field of
vision, not limited in either eye; acuteness of vision, nor



262


COLOR-BLINDNESS:


mal; refraction, normal; color-perception, at least four-fifths
according to Donders's method. For b, eyes and eyelids externally healthy, without habitual congestion or inflammation; field of vision, not limited in either eye; normal
acuteness of vision in one eye; normal refraction; colorperception, at least three-fifths; with the other eye, acuteness of vision at least one-half; color-perception, one-half.
These examinations are required by the royal
official regulations of Jan. 31, 1879, published in
the "Nederlandische Staats-Courant" of March
3, 1879, chap. v. art. 85:" All employes must be able to read and write and possess normal power of vision, so far as this is required for
the proper performance of their duty.
"Employes who, by the decision of the minister of the
department of industry, commerce, and the navy, are considered unfit to perform their duty, are, at the request of
the minister, to be discharged by the managers of the railroads."
Regulations were also proposed to the government by Professor Donders in reference to the
navy and merchant marine; and they are now
accepted and enforced, as seen from an order in
the same official paper:" The minister of the department of industry, commerce,
and the navy, referring to art. 2_of the royal decree of Feb.
17, 1879 (Staatsblad, No. 37), in regard to the carrying
out directions for the examination for a warrant as mate in
the merchant marine, as directed by royal order of May 5,
1877 (Staatsblad, No. 98), has decided to require, -
" 1st, In the test for visual acuteness and color-sensation
ordered in the article, the following: —
"a -Normal vision without correcting glasses with one
eye, and at least one-half of normal vision with the other
eye.
"b - Both eyes must be without manifest hypermetropia
of a degree above D 1.00, and in one eye at least nominal
vision.




ITS DANGERS AND ITS DETECTION.          263
" c -Visual field not limited in either eye.
"d -Eyes and eyelids externally healthy, without habitual congestion or irritation.
" e - Color-perception perfect for transmitted light in one
eye, and at least one-half in the other; according to Donders's method.
"2d. The report and declaration of the expert, as required in the above, shall be considered valid for one month
only from the time the test is made.
"TAK VAN POORTVLIET.
"GnAvzNiAGE, Feb. 27,1879."
By the same order three ophthalmic surgeons
are appointed as the experts for these examinations in Amsterdam, Rotterdam, and Leeuwarden.
In England, Parliament has never enacted any
laws in reference to the control of color-blindness
among railway employds or the navy and mercantile marine, so far as I can at present ascertain.
The individual railroad corporations have, however, taken steps in this direction in regard to
their men. Professor Wilson says, in 1856, " I am
happy to say that the publication of my papers
has induced the Great Northern Railway Company
to require that in future all their porters shall be
tested as to their freedom from color-blindness
before they are admitted."
A terrible accident at Arlsey, Dec. 23, 1876,
called out replies from railroad-surgeons to newspaper articles in reference to this point of control.
In " The London Times " of Jan. 1,1877, Mr. S. L.
Mason writes, -
"The risks incident to the peculiar physical defect
known as color-blindness, railway managers have long been
alive to. On our leading lines, without exception, precautions are taken against the employment of men subject to
that disqualification. In Mr. Seymour Clark's time, when




264


COLOR-BLINDNESS:


I was connected with the Great Northern Railway, this
matter was scrupulously attended to, and, no doubt, is so still
under the present able management. At the date I speak
of - ten years ago - no porter, even though destined to
work in a goods-shed, would be certified as eligible for appointment by the board until his eyesight should have been
subjected to certain prescribed tests, among which was the
discrimination of colors, especially those used in railwaysignals."
Other testimony was given in "The Times,"
"The Lancet," &c., that railroad employ4s were
tested on several different lines by Mr. Oliver
Pemberton of Birmingham, Mr. C. Puzey of Liverpool, Mr. Page of Carlisle, and Dr. Jaspar McAldin. In the medical discussions, however, it
was shown that the tests applied to detect colorblindness were very faulty and wholly inadequate.
In consequence of the use of methods requiring
only the color-name of objects or railroad-signals,
the surgeons were deceived into the idea that colorblindness was not as frequent as Professor Wilson
had shown it to be. The public fears excited at
the time of the Arlsey accident were thereby unfortunately quieted. No better proof is needed of
the necessity of a uniform and certain test being
applied to employ4s than the facts and discussions
of the Arlsey accident.
Dr. D. Argyll Robertson of Edinburgh kindly
writes me of date March 9, 1879, -
" I trust that the following facts, which I have ascertained
through the surgeons to the North-British (Dr. Dunsmure)
and the Caledonian (Dr. John Duncan) Railway Companies,
may be of service to you. I may mention that these are the
two chief railway companies in Scotland; the North-British
possessing 930 miles of railway, and the Caledonian 753
miles.




ITS DANGERS AND ITS DETECTION.           265
NORTH-BRITISH RAILWAY. - Since about 1865 or 1866,
when Dr. Dunsmure directed the attention of the manager of
the company to the subject, both engine-drivers and stokers
are invariably examined as to color-perception before being
engaged. The men are tested by means of a board with
ten different colors upon it. Three men have been rejected
on account of color-blindness since examinations were instituted.
"CALEDONIAN RAILWAY COMPANY. - Before any one
is employed as signal-man or guard, he is first examined by
a doctor, and especially as to his sight, and power of distinguishing colors. Only about one in a year is rejected on
account of color-blindness.
" All engine-drivers are tested as regards perception of
color when they are passed from 'firing' to 'driving,' and
no case of color-blindness has yet been met with. This,
however, is probably due to the circumstance that the men
are aware that they are to be tested, and do not persevere
as stokers if they considered they were not competent to
pass as drivers.... There is no legislation here enforcing
such examinations."
Abundant proof has been given in this volume
of the inadequacy of such tests as are thus shown
to be at present used on these Scotch roads, as
well as on the various English roads, from the
evidence of the surgeons connected with them.
No wonder so few color-blind are detected. A
simple act of Parliament enforcing universally
such a test as Holmgren's or Donders's would
insure safety, as the medical officers of the roads
are perfectly competent to properly carry out such
examinations.
" Order of the Handelministerium of Prussia, March, 1877,
published in the Official Paper of the Government of the
Interior, 1877.
" In consequence of the frequent occurrence of cases of
so-called color-blindness, and the great dangers which may
arise from the same on the railroads, it is recommended, -




266


COLOR-BLINDNESS:


" 1st, That persons in the outside railroad service, such
as station officials, pointsmen, signal-men, engineers, stokers,
brakemen, and conductors, be first tested as to their colorperception before being employed.
" 2d, That all those not engaged in the above-mentioned
positions be tested for color-blindness, in order to eliminate
the red or green blind from positions where the recognition
of the colored signals is requisite.
"3d, This examination is also to be made of convalescents where it is requisite; namely, after typhus-fever, injuries of the head, severe contusions, and the like, as also
in general to be repeated every five years.
"If this examination is to be carried out over a large
district by a recognized ophthalmic surgeon, it would necessitate numerous journeys of the officials and employes, and
cost much time, It is suggested that it is within the proposal of the imperial direction to consider that any physician, even if he has not made a specialty of diseases of the
eye, can carry out this test with sufficient exactness to insure
safety: therefore the imperial railroad directory is advised
to have the proposed examination conducted by the several
district railroad-surgeons."
In accordance with the order of the Handelministerium of Sept. 19, 1877,
" The examination is to decide whether the person tested
can correctly distinguish red, green, and violet by daylight,
and also by artificial light, or whether there is the slightest
suspicion of color-blindness: therefore the examination
must be done by an ophthalmic surgeon."
In reference to the regulations and instructions
for these examinations, I will quQte from Dr.
Magnus of Breslau, as what he states is pertinent
to all such tests, and therefore extremely important
for us here in the United States, where the whole
subject is new. He says," The very great necessity of good color-perception on the
part of railroad employes, concerning as it does the safety
of the public roads, has already excited general attention,




ITS DANGERS AND ITS DETECTION.             267
thanks to the untiring efforts of Professor Holmgren. And
it has led already to valuable practical measures; but yet it
has seemed to us, that, precisely on this point, certain reforms are very desirable. The regulations from the authorities for the purpose of avoiding the possible results of
the action of color-blind officials are, and rightly so, first
directed towards a most careful test of the color-sense of
all the employes. All candidates are to be examined, and
all those in service equally thoroughly tried for colorblindness. A similar examination of the whole personnel
is to be carried out every five years. A general examination for color-blindness is directed by the regulations of the
authorities. The method and the way and means of conducting this examination are, however, undetermined. The
choice of methods is rather left to the fancy of the examining surgeon; or, if a method is advised him, this is not
always the same, the several railroad managers varying
greatly in this respect. But the result of every test for
color-perception is very dependent upon the method employed. Now, the various methods at present used are not
of the same value. Some of them, on the contrary, give
very unreliable results; whilst others leave but little to be
desired in respect to precision. Hence the values of the
reports of the several examinations on the various German
roads are not the same, but exhibit great and doubtful
variations. If we could compare the percentage from the
statistics of all the German roads of the extent of colorblindness, we should see within what limits such percentage
varies, and how the results of the individual examiners
differ. For example, " The Breslau Journal" of Oct. 10,
1878, reports the test of 1,348 employes of one of the roads
here, and the finding of but 10 color-blind (or 0.74 per
cent); whilst one of my colleagues, who tested the employes
of another road, told me he found 4 per cent.
" We see, therefore, that the test for color-blindness, as it
is now carried out on our German roads, does not fulfil the
object desired. Absolute safety of the traffic, with due regard
to the interests of the personnel, cannot be gained by such
differing and uncertain data. To obtain the great benefit of
an obligatory examination of the color-sense of the railroad
employes, the varying reports as to the extent of color-blind



268


COLOR-BLINDNESS:


ness must be corrected, and greater unity obtained. This
can only be done by one and the same method being required
on all our roads. Hence it will be asked, which of the present
methods is most practical, and has so stood the test of employment as to be naturally called for in the interest of
the safety of the public communications? The answer to
this very important question will be governed by a critical
analysis of the several methods of testing. In my examination of 5,486 persons I have very particularly considered this
very point, and, from my experience, decided that the method
of Professor Holmgren of Upsala is the one giving us the
most exact results in testing large numbers. It is so superior to the other present methods, in exactness of result
and convenience of use, as to render it undoubtedly the
best. In such an important question the opinion of a single
observer should not, of course, be taken alone, but others'
experience also heard and considered. In doing this we
shall find similar favorable opinions of Holmgren's method
from those who have used it. Thus Dr. Cohn, in Breslau,
in his criticism of the several methods of testing, declares
Holmgren's to be the best. We hear the same from Professor
Pfliger in Berne, and from Dr. Jeffries in Boston. The latter
is so convinced of the superiority of Holmgren's method,
that he writes me of date Sept. 19, 1878, from Boston, as
follows: 'My own experience teaches me the great value of
Holmgren's method over all others, and I wish it would be
ordered by your Kaiser throughout Deutschland.'
"In interest, therefore, of the safety of railroad travel, we
feel called upon to require the following: That the test for
color-blindness now obligatory on most of the German roads
should be the same and identical throughout the empire,
and carried out in the same way on every railroad; and that
Holmgren's method, being the most certain and most preferabl, should be alone employed for this purpose."
The value and truth of this quite moderate
criticism of Dr. Magnus can best be proved by
showing what has been done on a number of the
German roads. This I am enabled to do from a
lecture given by Dr. E. Gintl, Central Inspector




ITS DANGERS AND ITS DETECTION.      269
of the Lemberg-Czernowitz-Jassy road at Vienna,
April 2, 1878, before the society of Austrian railroad officials. After an introductory sketch of
color-perception, &c., and some of the methods
of testing for color-blindness, he says, "It will
thus be seen, that, for the examination of the employes in general, any of the methods may be used.
Stilling's or Holmgren's tables, or the colored
charts, or Waldstein's apparatus, are quite sufficient; but, to decide the doubtful cases or the individual colors, only the spectroscopic apparatus of
Schmidt and Hausch in Berlin can be employed
with certainty, as I have personally proved in the
testing of a very large number of persons." He
gathered the reports from forty-six railroads, on
which 41,444 employes were tested, and 319 colorblind found, - a percentage of 0.769. I here give
these reports: -




Date of    Number i No.      PRemar                             ks to those found ColorNo.    Name of Railroad.     Date of    Number            Per    Method of Testing   Remarks as to those found ColorTest.     Tested.   Blind. Cent.       employed.              blind April, 1878.
Get-maBlnRad.


1
2
3
4
5
6
7


German Roads.
Badische Staatsbahn
Baierische Staatsbahn.
Berg-Markische Bahn
Berlin-Anhalt
Berlin-Gorlitz
Berlin-Hamburg
Berlin-Potsd.-Magdeburg


July, 1877,
June, 1876,
July, 1877,
June, 1877,
Sept., 1877,


2,658
77
465
1,735
2,910
4,200
5,107


12


6.45
2.15
0.63


Stiiling's tables
Vierordt's     spectro.
scope
Stilling's tables
Colored-paper tables.


8   Berlin-Stettin.


10
11
3
85
56


0.10   Colored-paper tables.


New employes to be tested; old
not yet examined.
January, 1878, not yet commenced
the tests for color-blindness.
Examination not yet finished.
8 red, 2 blue-yellow, 2 blue-black
blind.
2 red-green; 8 confound only
shades of color.
7 red-green, 1 green-blue, 1 violetred, 1 yellow-red, 1 violet-black
blind.
1 confounds all complementary
colors; 1 orange-blue, 1 yellow.
blue blind.
Confounds color-tones. No color.
blind in strictest sense.
Tests not yet finished.
18 confound all complementary
colors; 22 red-green, 15 redblue, 1 left eye red-green blind.
Tests not yet finished.
3 red-green-blind; 3 could not distinguish any color.
Tests not yet finished.


0
0
0
t)
ri2..


9
10
11


Coln-Minden.
Elsass-Lothringen.
Hanover Staatsbahn. Aug., 1877,. July, 1877,


2.02
1.10


Stilling's tables.
Stilling's tables; Vier.
ordt's spectroscope.
Colored   tables  and
glasses..
Colored tables and
glasses


12  Hessische Ludwigbahn. Dec., 1877,.
13  Liibek-Bichen-Hamb'g. Dec. 1877,        496


26    i.2i


14  Magdeburg-Halbstadter, Dec., 1877,




15  Nassau u. Taunus Bahn, July, 1877,    1,808
16  Niedermarkische Bahn. Dec., 1877,
17  Obsschlesische Bahn. Dec., 1877,..
18  Oldenburgische.. Aug., 1877,    800
19  Ost-bahn, preuss.. June, 1877,    6,287


20
21
22
23
24
25
26
27
28
29


Pfalzische Eisenbahn
Rechte Oder Uferbahn.
Rheinische Eisenbahn.
Saarbrucken Eisenbahn,
Sichs. Staatsbahn.
Thiiringische Eisenbahn,
Weimar-Gera Eisenbahn,
Werra Eisenbahn.
Westphalische Eisenb.
Wiirttemburg Staatsb.


Mar., 1878,
July, 1877,
June, 1877,
Oct., 1877,
July, 1877,
Jan., 1877,


880
1,457
1,500
68
719
*o


6
14
45
I '
1
8
3
1
7


0.46   Colored  tables  and
glasses..   Stilling's, Vierordt's
1.75  Colored-paper tables.
0.75   Stilling's tables and
colored papers


6.1i
0.55
06.20
1.47
0.97


Green and red glasses,
and targets
Green and red glasses,
and targets
Stilling, Vierordt
Stilling's tables.
Stilling's tables
Stillings tables


All red-green-blind.
Tests not finished.
Tests not finished.
3 red-green; 10 blue-green; 1 yellow.green.
29 red-green; 1 blue-orange; 1
violet-yellow; 5 blue-green; 1
blue-yellow; 8 could not distinguish.
Tests not finished.
Red-green-blind.
No report made.
4 red-green; 1 uncertain in blue;
1 red-blue; 1 uncertain in yellow; 1 without color-sense.
No official examination.
1 red.green and red-blue, 2 redgreen blind.
Blue-red and yellow-green blind.
All red-green-blind.
Tests not finished.
From January, 1877, new employes
to be tested; old ones not.


M
ct
02
o
02
C!.I, I


Total.          I..  30,590


268    0.876








No.


Name of Railroad.


Date of    Number      Ao.   Per     Method of Testing
Test.     Tested.   Blr. Cent.         employed.
Tse.Blind.




Austrian and Hungarian.
30 Oester.-ung Bahnen


31
32
33


Bohmische Nordbahn.
Bohmische Westbahn.
Buschtiehrader Eisenb.


Jan., 1878,
Oct., 1877,
July, 1877,


540
1,514
700


1
3


0.19
0.20


34 Carl.Ludwig.bahn.
35  Franz-Joseph-bahn
36 Nordbahn. Aug., 1876,


Colored papers and
glasses
Colored papers and
glasses.
Colored yarns, Vier.
ordt's
Signal-glasses; Waldheim's   chromatoscope, and Vierordt's
Colored paper, Stilling's tables.
Vierordt's spectroskop
Signal targets and
glasses.
Waldheim's chromatoscope


--.
Remarks as to those found Color-.
blind.
Test not finished.
Green-blue-blind.
Q
1 red-green; 2 completely color-  0
blind.
Tests not finished.               ~
No tests yet made.
Only new employ6s tested. Uncertainty in deciding tones.    G
Test not finihed
Tests not finished.
Tests not finished.
1 red-green-blind. Examination
going on.
Given up for practical reasons.
20 did not recognize the violet;
1 did not recognize the green;
1 did not recognize the blue.
5 red-green; 3 green-blue; 4 blackgreen; 4 uncertain; 1 no colorsense.


37
38
39
40
41


Elisabethbahn
Kaschau-Oderberger B.
Lemb-Czernow-Jassy B.
Rudolfbahn.
Nordwestbahn


Dec., 1876, Notgiven,


Dec., 1876,
May, 1877,
Oct., 1877,
June, 1877,


Notgiven,
1,678


1


0.06


42   Oester. Staatabahn


5,601


39


0.70  Colored papers and
glasses.




43  Sudbahn..                                                                        Test not yet finished.
44  Turnau-Kraulp Eisenb. Nov., 1877,       854        1     0.28  Colored papers.      For all complementary colors.
45  Ung. Nordostbahn.................Test not yet finished.
46  Ungar-Staatsbahn.       Aug., 1877,   1,167       6.5   Dri. Gross's colored
lamps..    2 red-green, 4 green-blue blind.
Total......   10,854      51    0.489.....
Q
0
O




274


COLOR-BLINDNESS:


Contrasting these results with those where a
a thorough test gave us as in France 5.77, in
Switzerland 6.28, in Sweden 2.15, and in Finland 14.01, and we can readily appreciate the
force of Dr. Magnus's criticism, and my remark
above, that but here and there can the color-blind
employ4s have been detected on the German
roads.
I have also given this long list of railroad examinations, collected by Dr. Gintl, as a warning
to our railroad corporations in this country, and
to the examiners they shall hereafter employ.
The several German railroads' surgeons, not being
officially directed to employ Holmgren's method,
and unfortunately hearing it spoken and written
about in a tone of doubt, naturally chose other
methods they individually knew of. Moreover,
some of the German physicians who had paid
especial attention to this subject, and who had
tested some thousands of persons for color-blindness by Holmgren's method, deliberately misapplied it, in absolute contradiction to his express
and very explicit directions.  Thus, to detect
whether a person is color-blind, we have seen. that
a peculiar shade of green worsted is used, and the
examined directed to pick out what looks like it,
lighter or darker. A purple (German, rosa) is
used to decide whether a person is red or green
blind. This latter is not to be used to detect
color-blindness, but only which form of the defect
we have. Nevertheless Dr. Cohn of Breslau, in
reporting his results to the Heidelberg Ophthalmological Society, 1878, says, "As the very best and
the quickest method of first testing for color



ITS DANGERS AND ITS DETECTION.     275
blindness, I must again and again recommend the
purple worsted. It has served perfectly." He also
speaks of the colored plate attached to Holmgren's book, and copied in this volume, as being
as bad to detect color-blindness with as the purple worsted is good. Now, this plate is only intended, and so most definitely described, to illustrate the colors to be used, and the colors of
confusion or mistakes of the defective.  This
ignoring Holmgren's explicit directions as to the
carrying out of the test with the green worsted,
and then speaking of the colored plate as if that
had been proposed to be used by Holmgren, was
most unfortunate and misleading. It has naturally
led others to follow him without reading Professor
Holmgren's book.   Dr. Cohn tried Stilling's, as
also other methods, but found, as every examiner
will, Holmgren's the most convenient and practical.
Thus the reports I have quoted of the German
roads show most conclusively that from a faulty
method of testing only here and there, so to
speak, have the color-blind employes been detected. This is very unfortunate, as it throws, for
the time being, a certain doubt over the whole
question of the frequency of color-blindness, its
danger, the necessity for control, and the elimination of the defective. Moreover, the entire work
in Germany will have to be done over again.
Probably, from what I lately learn, the correct
tests are now being officially ordered, and carried
out. Thanks to the energy of Professor Holmgren in Sweden, the affair was there better conducted.  The government first ordered the use




276


COLOR-BLINDNESS:


of the flags and lanterns by the railroad officials
to test for color-blindness; but, when Holmgren
showed them the uselessness of this, they ordered
his test, and also required all the railroad-surgeons to learn it of him, and carry it out properly.
From a lecture on color-blindness by Dr. A. von
Reuss of Vienna, and a letter of date March 17,
1879, I am able to still further substantiate the
criticisms I have made or introduced in reference
to the examinations of the German employes.
The Austrian Handelministerium ordered Nov.
18, 1876, that "persons who could not distinguish
the signals on account of near-sightedness or colorblindness were not to be admitted into the service." This led to the carrying-out of the examinations as above given with such unsatisfactory
results. Dr. von Reuss says," Why these differ so greatly from the numbers reported
by ophthalmic surgeons was readily seen from the original
reports sent in to Dr. Gintl, and which he kindly allowed
me to see, from which reports the data of the tables were
collected. In these reports are mentioned blue-red-blind,
blue-black-blind, green-blue-blind, violet-black-blind, yellow-red-blind, &c., and this where Stilling's tables had not
been used, which might have given rise to such confusion.
This is a proof that the examiners did not know what they
were about. The majority of the examinations are therefore useless."
In this lecture Dr. von Reuss reports testing
593 employes, and finding 3.2 per cent color-blind.
In his letter to me of March 17, 1879, he says, "I
have tested 600 employes of the Elizabeth-Westbahn, and found 3.5 per cent color-blind." He
employed Professor Donders's method with the
worsteds.




ITS DANGERS AND ITS DETECTION.           277
The unsatisfactory results of the examinations
by the several railroad-surgeons, due to a want of
knowledge and the lack of a uniform and certain
test, led to the following order from the Handelministerium: -
ORDER OF THE HANDELMINISTERIUM, OCT. 15, 1878, TO
ALL THE RAILROAD CORPORATIONS, RESPECTING PROFESSOR HOLMGRBEN'S METHOD OF TESTING COLOR-BLINDNESS.
My frequent attention having been called to the work of
Professor Holmgren, " De la Cecite," &c., I have obtained
professional opinions as to the method of testing color-blindness proposed in it, showing it to be practical and very simple, and perfectly answering the requirements. The method
consists in causing the examined to select from a number of
skeins of colored worsteds all those corresponding to a pattern shown him. The examiner decides from the manner in
which this is done. A normal-eyed will select four or five
skeins in a minute, and the color-blind will as quickly make
such characteristic mistakes as to render the immediate
diagnosis possible. In doubtful cases, and where deception
is supposed, a more thorough test must be applied, with, for
instance, a spectrum apparatus.
As experience has shown that color-blindness, besides
being congenital, may be acquired, safety requires that not
only should those entering service be tested as to their perception of the three primary colors,- red, green, and violet,
- but that the test should be repeated periodically, and
especially after diseases, and contusions of the head.
I desire to call the attention of the corporations to the
book above mentioned, and would ask their consideration of
the suggestions here briefly made, since, from the necessary
apparatus, the examinations of employsd has hitherto been
expensive and inconvenient; and this method therein proposed greatly simplifies and facilitates the testing for colorblindness.
K.-K. Handelminister CHLUMETZKY.
VIENNA, Oct. 15, 1878.
Jan. 8, 1879, in the House of Representatives




278


COLOR-BLINDNESS:


of the legislature of Massachusetts, Mr. Hamilton
A. Hill of Boston introduced, at my request, the
following order:" That the Committee on Railroads inquire whether any
and (if any) what legislation is necessary in reference to the
employment by railroad companies, in certain responsible
positions, of persons affected with color-blindness."
This order was passed by the House, and a public hearing given as follows:
COMMONWEALTH OF MASSACHUSETTS.
COMMITTEE ON RAILROADS.
STATE HOUSE, BOSTON, Jan. 13, 1879.
The Committee on Railroads will give a hearing to parties interested in an order relative to legislation in reference
to the employment by railroad corporations, in certain responsible positions, of persons afflicted with color-blindness,
at room No. 10, State House, on Wednesday, Jan. 22, at ten
o'clock A.M.
EDWIN W. MARSH,
Clerk of the Committee.
By invitation of the Committee on Railroads I
appeared at this hearing, and argued in support of
the conclusions contained in this volume. My
statements were supported by European statistics,
and my own collected in this community, by experiments in reference to color-perception, the
exhibition of various tests, &c., and by the practical
illustration of the value, of Professor Holmgren's
method in detecting the chromatic vision of several color-blind who were present at the time.
There was no opposition to my statements or conclusions.
As the result of this hearing, the Joint Committee on Railroads reported, Feb. 28, 1879, in the
Senate, the following resolve:



ITS DANGERS AND ITS DETECTION.         279
"That the board of railroad commissioners be instructed
to consider whether any legislation is expedient or needful
with reference to the employment by railroad corporations
of persons afflicted with color-blindness."
This was passed in the House of Representatives March 21, 1879, and in the Senate March 24,
1879; receiving the signature of the governor
March 25, 1879.
It is thus seen that Massachusetts has been the
first State to take action in reference to the control of color-blindness on the railroads. She possesses, of course, no authority on the water. There
the General Government must act in concert with
other nations. It is now in the hands of the Massachusetts railroad commissioners to carry forward the work of investigation, and report hereafter to the legislature. If they can induce the
several railroad corporations to meet the just
demands of the community, and eliminate the
color-blind from their employ, then a law, subsequently enacted, can be based upon the result of
the examinations, and made to meet all requirements of the future. This law of control should
also, as in Europe, require the proof by test, of
normal visual power for form, as well as normal
color-sense.
It is to be hoped that the other States will
quickly follow the action of Massachusetts. The
advantages of a uniform law throughout the
country, and a uniform and absolutely certain
system of testing for color-blindness, I need not
dwell upon here, since it is self-evident from what
I have brought forward in this volume.      There
will be no excuse for such blunders as were made




280           COLOR-BLINDNESS:
in Europe, now that we have the benefit of them
in this country.
I have spoken of my action and its results, in
order that my professional brethren in other States
may see how my efforts were successfully carried
out, and be able to refer to them when themselves
undertaking similar work in their own communities.




ITS DANGERS AND ITS DETECTION.


281


CHAPTER XXIV.
PERSONAL EXPERIENCE WITH HOLMGREN'S METHOD. - SUGGESTIONS AS TO ITS USE.
THE experience which I have gained in the use
of Holmgren's method of detecting color-blindness
by the worsteds is, I think, worth here recording
for the benefit of my brother ophthalmic surgeons,
whom the railroads may hereafter ask to test the
employ6s of their roads. First, as to the choice of
the worsteds themselves, since a good deal depends
on this: Proper colors can be obtained directly
from Fraulein Letty Oldberg, in Upsala, Sweden,
for about 5 crowns 63 pfennigs. Such a selection
was sent me by Professor Holmgren; and similar
ones I have made here, and used in my testing.
The colors of the green and purple test in the colored plate in the Swedish, French, and German
editions of Professor Holmgren's book, are apt
not to be correct, and may mislead any one.
This arises from the difficulty of reproducing in
chromo-lithography the precise tints, and rendering these permanent.
To learn the test, I would strongly advise, not a
simple perusal, but a careful and repeated study




282


COLOR-BLINDNESS:


of Holmgren's directions and explanations given
in this volume. They may at first seem rather prolix; but experience will soon show how valuable
his minute directions are, which, when properly
studied, will relieve many a doubt, and clear up
many a seeming discrepancy in our actual test of
old or young. When thoroughly understood theoretically, it will be found quite simple, and readily
adapted to test even very young children with;
as, for instance, primary-school children. I would
advise first commencing with educated adults, and
afterwards testing in the schools, where material
is more at hand and more manageable. We shall,
moreover, meet in the schools of lower social grade
just the sort of stupidity and lack of appreciation
which we are likely to meet among uneducated
railroad employ6s, sailors, and factory workmen.
It is a curious fact, which, I think, all who test
large numbers will sooner or later find out, that
dulness of comprehension and dulness of perception will almost invariably simulate color-blindness.
Many a teacher in our schools has been greatly surprised that I have not marked as color-blind a boy
who seemed to them to do about the same as the
color-blind, but who had thrown out with the pattern a single worsted, which quickly told me that
I had to deal with stupidity, and not a chromatic
defect. It has been often very hard to disprove
the story the worsteds picked out told, when that
story was dictated by mental dulness. The teachers generally found that I selected their brightest
scholars as such.
There is besides this a dulness of color-perception, or rather a peculiar slowness in the colors




ITS DANGERS AND ITS DETECTION.       283
taking effect, so to speak, which is at first confusing to the examiner, unless he bears it constantly
in mind, and is familiar with it. It is difficult to
describe, but is yet readily recognized. All this
adds to the danger of our considering that we have
at least partial color-blindness before us, and hence
increasing our ratio at the expense of truth. As
inexperience and stupidity will most trouble us in
the younger classes of. lowest social grades, I
would advise commencing with the oldest students one can avail themselves of, and then going
to the high schools before the grammar-schools.
At present I should be inclined to think, that,
however seemingly curious and interesting it might
prove, the testing for color-blindness, by even so
simple a method as this of Holmgren's, in the primary schools, would be time lost, as well as likely
to mislead one as to the relative proportion, &c.
Moreover, there are students and grammar-scholars enough in all our cities of any size to furnish
more than ample material. I ought to add here,
however, that I found no difficulty with the several hundred in the grammar-schools who had just
come from the primary; i.e., within a few days.
All my examinations were made with Holmgren's test. My purpose was to quickly obtain an
approximate estimate of the proportion of colorblind in our community, and at the same time to
disseminate a knowledge of the existence of such
a chromatic defect and its nature, in order to prepare the way for some action in reference to control on the railroads and in the marine. It has
been, except in a few instances of educated adults,
wholly impossible for me, at present, to test those




284


COLOR-BLINDNESS:


I found color-blind by other methods than Holmgren's. My own experience, however, and the
reports from Europe of the gentlemen there at
work in this investigation, confirm me in the
belief, that, whatever additional method I might
employ, I should not probably change my opinion
of the individual case of color-blindness. For the
purposes I have had in view, my time has been
better spent in continued work in our schools,
than in stopping to test over again, by additional
methods, persons so young as school-children from
eight to seventeen years of age. I hope, hereafter,
to accomplish more in testing the adult color-blind.
For a time I worked under a disadvantage in
reference to classifying the red and green blind,
because my purple worsted was not dark enough,
owing to the color having faded in the plate in
Holmgren's book, and thereby deceiving me. But
I supplemented this weak point in my decision by
having a red and a green worsted of as nearly as
possible the same degree of luminosity, and asking
the color-blind which was the darker, Their decision I generally found very quickly made, and
adhered to. I also asked them to pick out the
black worsteds, and found they would select the
dark greens or dark reds, according as they were
green or red blind. Since I have had the proper
shade of purple, this has not of course been necessary. I have, however, frequently carried it out
after deciding by the purple, in order to see how
accurate my previous division into red and green
probably was. I have decided I cannot be very
far from right, and therefore have given my
records as I made them. I did not make up the




ITS DANGERS AND ITS DETECTION.      285
tables till I had finished, and consequently did not
know what the relative proportion of red and
green blindness was during the time I was testing.
I have followed Holmgren in making three divisions, -complete red and green blindness, and
partial color-blindness. My three cases of violetblindness I have allowed to stand under partial
color-blindness. These I have found the test
readily showed. As color-blindness exists in all
degrees, so to speak, it would of course be possible, by careful special examination of each case, to
express its particular degree; as by Donders's method or by Holmgren's color-sense tester. The percentage of color-blindness, each examiner finds, will
be modified by where he draws the line; that is,
how feeble must the chromatic sense be to come
under the head of partial color-blindness, and also
what shall be regarded as feeble chromatic sense,
and what only dulness of perception. The greater
our experience, however, the more carefully can
we decide these points. Holmgren's method with
a pretty large number of worsteds has seemed to
me to be particularly well adapted for this purpose. I have kept to the original plan of having
a large number of green worsteds, finding that for
my purposes it worked best; and I was willing to
give the extra time, in consideration of the psychological study it afforded me. Professor Holmgren has spoken of this. I am not certain that
with young people it is not best, since as much
time is wasted by their searching for the three or
four greens in Holmgren's modified method, as in
throwing out all or a decisive number of the
greens when there are many of them. I think,




286


COLOR-BLINDNESS:


also, it gives the examiner a better chance to
watch the play of the hands, from which so much
can be deduced.
It may not be amiss if I say I use about a hundred and fifty skeins of worsted, and carry them,
wrapped in a piece of white cotton cloth, which can
be spread over a table or other surface. On this the
colors show well in contrast. When statistics are
being gathered, or large numbers must be tested
with the smallest loss of time, this plan will save
trouble, and thereby add to the total number examined. Even amongst the youngest scholars,and several hundred were just from the primary
schools,-I have not failed to convince myself,
and show to the teachers, color-blindness where it
existed. It is useless, I think, to argue with those
of my European friends who still think they can
always detect a lack of chromatic power by Stilling's tables or other method. Their number, I believe, will become steadily less when they take hold
of Holmgren's test in earnest, and carry it out as
directed by him; as has, for instance, my friend, Dr.
Magnus of Breslau. My experience teaches me to
advise my ophthalmic brethren, or other physicians
who will be called upon to carry out the work I
have commenced in this country, to waste no time
with other methods, but to fully and carefully
familiarize themselves first theoretically with Holmgren's test, and then practically commencing with
adults.




ITS DANGERS AND ITS DETECTION.


287


CHAPTER XXV.
CONCLUSIONS AND RECAPITULATION.
ONE male in twenty-five is color-blind in a greater
or less degree.
Of this defect they may even themselves be
wholly unconscious.
This blindness is red, green, or violet blindness.
Total color-blindness also occurs.
This defect is congenital. It exists in varying
degrees. It is largely hereditary. It may also be
temporarily or permanently caused by disease or
injury.
It is incurable when congenital. Exercising the
eyes with colors, and the ears with their names,
helps the color-blind to supplement their eyes, but
does not change or increase their color-perception.
Experiment and experience show that we are
forced to use red and green marine signal-lights to
designate a vessel's direction of motion and movements, and at least red lights on railways to designate danger.
Form, instead of color, cannot be used for these
purposes.
There are many peculiar conditions under which




288


COLOR-BLINDNESS:


railroad employ6s and mariners perform their duty,
which render colored signals, and especially colored
lights, difficult to be correctly seen.
These signals can never be correctly seen by the
color-blind. There are such among railroad employ6s.
There is, therefore, great danger from colorblindness.
Railway and marine accidents have occurred
from it.
There is no protection but the elimination, from
the personnel of railways and vessels, of all persons whose position requires perfect color-perception, and who fail to possess this. This can now
be readily and speedily done.
Therefore, through a law of the legislature,
orders from state railroad commissioners, or by the
rules and regulations of the railroad corporations
themselves, each and every employ6 should be
carefully tested for color-blindness by an expert
competent to detect it. The test and the method
of application should be uniform. All deficient
should be removed from their posts of danger.
Every person offering himself as an employd should
be tested for color-blindness, and refused if he has
it. Every employ6 who has had any severe illness,
or who has been injured, should be tested again
for color-blindness before he is allowed to resume
his duties. Periodic examinations of the whole
personnel should also be required.
Such regulations are generally in force on the
European railroads.
An international commission should be called to




ITS DANGERS AND ITS DETECTION.      289
establish rules for the control of color-blindness
on the sea, and the carrying out the same examinations amongst pilots, masters, and crews of
steamers and sailing-vessels, in the navies and the
merchant marine.




t




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INDEX.


A.
Page
Accidents cause color-blindness, 49
Accidents on the ocean.   161
Admiral, British service, colorblind....14
Alcohol causes color-blindness. 49
Alien Grant, color-sense..91
American statistics.  68, 75, 78
Automatic color-signals.. 20
Applicants for railroad service,
testing.....232
Army, control in..         177
Army, U.S., soldiers color-blind, 78
Aubert, idea of color-blindness, 65
B.
Babbage's account of Dalton.  8
Blank forms for tests... 261
Blind, the, use of color names, 97, 98
Blind, the, using other senses. 122
Blindness, red, green, violet. 30
Blindness, total, for color.. 35
Board of Health, Mass., Report, 80
Burnett, Dr. S. M., color-blind
negroes... 68
C.
Cohn on heredity... 61
Cohn's test..... 194
Cohn's use of contrast... 189
Cohn's chromasciopticon.. 189
Collisions on the sea.. 161
Color-blind, color-sense of.. 47
Condition of vision of.. 43
Engineer.... 152, 153
Former classification of, by
Seebeck, Szokalski, Purkinje, and Wartman.   22-25
Precise condition of vision of, 43
Present classification by
Young-Helmholtz theory, 26-41


Page
Color-blind, railroad employ6s,
how they escape danger 153-160
Their relation to railroad signals.....150
Sea-captain.... 52
Color-blindness, accidents from
on ocean...   161
Dangers from, on land.. 137
Dangers from, on ocean.  161
Frequency among railroad employ6s..... 142
No control of, in United States, 176
Not discussed by press.. 138
Concealment of..   88-110-237
Curability of, Favre.. 111
Physical peculiarities of, Cohn,
Magnus, Pfliiger, Holmgren. 65
Frequency in males..      69-79
From disease andinjury,Favre,
Wilson, Hays, Cooper, Walton..... 49-52
Hereditary, Earle, Dalton,
Cunier, Hochecher, Wilson,
Horner, Cohn, Magnus,    54-63
Hereditary in females.. 57
In colored race...     68
In European women.    85
In school-girls... 87
Incurability of.. 11, 123-124
Palliation of...  125
Palliation of, by colored glass, 126
Palliation by colored fluids, 129-136
Palliation of, by night light
128-129
Infrequency in females    80-87
Violet blindness.       77, 79
Color-names...       90, 97
By the blind...97-100
In schools....123
Colquhoun's, Dr., case.  9
Cunard Steamship Co..     2 58
Cunier, cases of color-blind fe
males.... 56
309




310


INDEX.


D.
Daae, Dr., color-blindness on the
ocean.....165
Per cent, Norway... 73
Daae's test.....194
Dalton's case...  4,117
per cent.....69
Dangers from color-blindness. 137
Delbceufand Spring, palliation of
color-blindness..  129
Disease causing color-blindness, 50
Difficulty of control in U. S.. 176
Donders's method, 191, 195, 246-250
Dor, Dr. H., per cent..   81
Dor and Favre's test...191
Dove's per cent...   70
E.
Earle, Dr. Pliny's family.. 54
Employes, railway, color-blind,
142-147
Railway, color-blind, condition
of.....148-153
Railway, already in service. 233
Railway, already in service,
testing.... 232
Engineer, color-blind, 152,153,160
Engraver, color-blind... 13
F.
Favre, Dr., color-blind sailors. 163
Cure of color-blindness. 111-114
Report of Lyons Railroad. 260
Females rarely color-blind.  85, 87
Feris, Dr., color-blind sailors. 163
Per cent.....72
Feigning color-blindness.. 237
Fick's theory.... 198
Finland, color-blindness in. 146
Fog, effect of, on colors.. 162
Fontenoy, Dr., per cent.. 73
Forbes, effect of steam.. 154
Form for color in signals.  171
Forster's perimeter... 197
Fuchsine, solution of, to palliate
color-blindness... 130
G.
Gallet, Lieut., per cent..72
Git, M., per cent.... 71
Gintl, Dr., report... 269
Goubert, Dr., treatment of colorblindness.... 120
Gould, Dr. B. A., color-blindness in U. S. soldiers..72
Guillot, per cent... 72
H.
Handelministerium of Austria. 277
of Prussia..... 265
Harris case, Huddart's account
of......  2


Hays, Dr., case of color-blindness.....50
Herschel, Sir John, remarks on
Mr. Pole's case... 46
Helmholtz, Prof., use of names in
test......115
Theory of color-sense.. 26
Hirschberg's spectroscope.. 190
Hochecher, Dr., color-blind family......  57
Holmgren's experience with color-blind employes..145
Holmgren, Prof., Young-Helmholtz theory....26
Criticism of Dr. Favre.. 121
On change of signals. 167-174
Color-blindness among females, 82
Color-names.... 94
Holngren on methods of testing,
183-188, 196, 201-219
Holmgren's chromatoskiameter, 241
Special directions for testing,
221-231
Former publications. 196-200
Measurement of color-blind. 66
Homer's law of heredity.. 58
Cases.....   59, 60
I.
Incurability of color-blindness. 111
Infrequency of color-blindness in
females....      80
International commission. 165, 288
J.
Javal, criticism of Delbceuf. 136
Jeffries, per cent..   74, 75, 87
Jews color-blind...   58-76
K.
Kelland, Prof., per cent.. 69
Krohn, Dr., per cent, Finland, 73-146
L.
Laws of control on railroads in
Europe.....251
Sweden... 252-254
Norway.....257
Bavaria.....258
Italy......259
Belgium.....259
Holland.....261
England.       263-265
Prussia..... 265
Laws of control in navies of
Europe.....255
Sweden. 255-257
Norway.. 257
France.....258
Holland.....262
Austria.....163
Lederer, Dr., report on colorblind sailors.... 163




INDEX.


311


Light and shade, value of, to color-blind.....104
M.
Magnus on heredity... 61
Criticism of German railroads, 266
Massachusetts, action of.. 178
Railroad Commissioners, 138, 279
Maxwell's color top.. 192
Marine signals, can they be
changed?.        166
Merchant marine.... 177
Methods of testing... 182
Meyer's law of contrast..189
Minder, Dr., per cent... 74
Employes..... 152
Mistakes of color-blind.     7
Wilson's reports of.     10-14
Author's reports of. *    17-21
Mixture of red and green lights
makes white....158
Mourand, per cent... 72
N.
Navy, control in....177
Holland.....262
France.....258
Norway.....257
Sweden.....255
Denmark..... 163
Austria.....163
Negroes color-blind... 68
Nelson, Mr. Thomas, notes on
color-blindness... 159
Niemetscheck, idea of colorblindness.... 66
Disproved by Cohn, PflUger,
lHolmgren...  67, 68
Nicholl, Dr., cases.   5, 6, 9, 10
Nickoll, helm-signals... 20
Nickel, chloride of, causes colorblindness.... 131
Noel warns as to color-blindness, 141
Number for color in signals. 172
P.
Parliament, no action of. 265
Peculiar look of color-blind. 67
Perkins Institution for the Blind,
test of color-names in.. 96
Pfliiger's measurements of colorblind..... 67
Use of contrast... 189
Physicians color-blind.   17-19
Pole, Mr., account of his own
case...        43
Post-office clerk color-blnd. 21
Practical life, color-blindness in, 88
Prevost, per cent.... 69
Prior on color-names..      90
Power, Dr. H., case... 109


Q.
Quaglino, Dr., color-blindness in
Italy..... 143
Quantitative determination, 241-246
Quakers, color-blind... 16
R.
Railroad Commissioners' report
on color-blindness.  138
Railroads in United States not
protected.... 176
Railroad signals, can they be
changed?....166
Railroad employes color-blind,
142-146
Perception of color-blind. 148
Raynaud, effect of fog.. 162
Relationship of color-blind. 66
Remedy, supposed, for colorblidness.... 133
Recapitulation... 286
Reuss, Dr., per cent..  143
Romberg, marine accidents. 161
Rose's color-measurer. 190
Rowe, Dr., per cent... 69
S.
Sailors color-blind..     163
Sanitary Commission, U.S. test
of color-blind... 78
School-girls color-blind.  85-87
School-boys color-blond     74-75
Schools, teaching colors in.  123
Scotch railroad, tests on..264
Schirmer's use of contrast..190
Scott, Mr. J., his own case..  4
Seebeck, Prof., classification of
color-blind.... 23
Test......192
Sea captains, color-blind.  52
Signals, marine and railroad, cannot be changed... 166
Spectrum shortened at violet end, 79
Steebach's colored glasses.. 126
Steam changes colors... 154
Stilling, Prof., warning as to
tests.....100
Per cent.....73
Use of shadows...188
Test......191
Surgeons, English railroad.  264
Sweden, color-blindness on railroads of.... 179
Szokalski, classification of colorblind.......      24
T.
Teaching colors in schools.. 123
Tobacco causes color-blindness, 50
Total color-blindness... 35
Tuberville's, Dr., case..  1
Tyndal red and green lights. 158




312                          INDEX.
U.                   Wartman, Prof. Elie, classificaUnited States Railroad signals. 175   tion    of color-indnes. 12
V                    Weber's use of contrast.. 189
Whewell's account of Dalton.  8
Ville du Havre, loss of, attributed  Wilson's tests....193
to color-blindness... 164   Woinow's test....192
Visual field, colors in... 37    Women, color-blind..     56
Color-zones of.... 38
Vineyard-Haven lights.. 20
W.                                  Y
Walton's case of color-blind engineer..... 62    Yobng-Helmholtz theory.. 26