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DEPARTMENT OF { |
GiIBRARY OF
i University of iilinones . bang
|
Books are not to be taken from the Library Room. & |
BeBe Daa SED
Pe 2. |
STUDIES IN MICROSCOPICAL SCIENCE.
STUDIES IN
MICKOSCOPICAL SCIENCE
?
EDITED BY
ARTHUR C. COLE, F.R.MS.
VO) Te EE
WITH THIRTY-SIX LITHOGRAPHED PLATES.
wee
LONDON :
BAILLIERE, TINDALL, AND COX,
20 KING WILLIAM STREET, STRAND, W.C.
1884.
[All rights reserved. |
PREFACE
The first volume of the “Stupizs 1n MioroscopicaL Science”
consisted of a series of Essays which, though each was complete in
itself, had little connection with each other. In the present volume an
attempt has been made, in the Sections devoted, respectively, to
Animal and Botanical Histology, to work out a special subject in so
far as the series of twelve short essays in each section admitted of such
treatment. My best thanks are due to Mr. W. Frarnuny, who con-
tributed the Section in Animal Histology; to Mr. Davin Houston,
F.LS., F.R.M.S., Lecturer on Botany and Biology at the Birkbeck
Institution, who undertook the Dotanical Section. Both these
gentlemen kindly contributed to the ‘* Poputar Srupius,” in which
Section also I was greatly assisted by Mr. Freprerick GreeEnrne,
Lecturer on Animal Morphology and Histology at the Birkbeck
Institution. Mr, Fearnley rendered most valuable assistance in respect
of the “Merrnops or MicroscopicaL Ruszarcu ;” whilst the very
elaborate and beautiful drawings from the preparations were contributed
by Mr. Epwarp T. Draper, to whom I offer my warmest acknowledg-
ments. The preparations were made by my son, Mr. Martin J. Core
(Instructor in Practical Microscopy at the Birkbeck Institution), and
myself. I desire to express my grateful sense of the very kind and
appreciative notices and reviews accorded to the “‘ Srupims” by the
Editors of the “JournaL oF THE Royat Mioroscopican Socrery,”
‘Science Gossip,” ‘‘InLustRaATED Science Monruty,” ‘Tue Micro-
scoPIcCAL News,” and numerous other Journals in this country and
America.
ARTHUR? Ge COI
TAA TS
CONTENTS
Srction J.-—ANIMAL HISTOLOGY.
The Morphology of the Cell
Blood of Frog $3
Epithelium
Cartilage
Areolar Tissue
Tendon
Adipose Tissue ...
Development of Bone
Nerve of Horse ...
Human Cerebellum
Human Cerebrum
Srcrion IJ.—BoTANICAL HIsTo.Loey.
The Morphology of the Cell—The Cell ae
The Cell as an Individual -
Morphology of Tissues
Primary Tissue
Epidermal Tissue
Vascicular Tissue
Fundamental Tissues
Secondary Tissue
PopuLAR MICROSCOPICAL STUDIES.
No 1,-—Hebridian Gneiss
Nos, 2 and 3.—The Human Sealy
No. 4.—Ovary of Poppy ..
Nos. 5 and 6.—Grain of Wheat
No. 7.—The Common Bulrush
No. 8.—The Intestine
No. 9.—The Crane Fly
No. 10, —Sponge
No. 1:.—Starch..
No. 12.—-The Dad: ler Plant
PAGES.
1— 9
9—12
13-16
lie
21-—24
25—27
29— 82
33—36
37—40
41—44
45—48
1-12
1s io
17—24
25 —28
29-—34
35—42
43—46
47—50
1— 6
7—14
15—20
21—28
29—31]
33—38
39—42
43—46
47—52
53—5b6
te
Vv
Plate ae
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EID ad nak Watson & Son. ith Burm
GLOBIGERINA OOZE.
Atlantic
AS
Sec.d Plate 2
POLYCYSTINA
Springh eld Barbados
STUDIES IN MICROSCOPICAL SCIENCE,
T
SECTION 1.—ANIMAL uistovocy.
pS nh ee ‘ / / ;
CHAPTER I. WWaaatitiire #38
THe MorpHo.toGy oF THE CELL. Sl ITS
Although the term histology’ literally signifies, a discourse about tissues
in general, its meaning in natural science is now limited to a considera-
tion of only the minute details of structure. Histology then, is pre-
eminently a microscopical science ; and animal histology is concerned
exclusively in the investigation of animal tissues.
As in physical science the chemist builds up his system of philosophy
out of atoms endowed with energy, so the histologist commences with
his elements,—cells imbued with life. A distinction must be drawn
between anatomical and physiological histology ; the former deals with
the shapes of cells and their relation to each other, the latter treats of
their functional activity or life. It is only with ‘anatomical histology
that we are at present concerned, and our first i Inquiry must be confined
to the ultimate element from which all tissues arise or are built up, and
which has been termed the morphological unit or cell.
THe Ceti Turory.—Since the discovery of the cellular nature of
animal tissues by Scowann2, in 1835, there has been much diversity of
opinion as to the true nature of the morphological unit. Some have
asserted that it consists of a minute mass of indifferentiated protoplasm ;
that is to say, protoplasm in its most elementary condition, without any
sign of structure,—not even a separation into an outer dense and an
inner soft layer ; others have taken up this primordial particle and have
held it to be the ultimate condition from whence every morphological
unit derives its existence, and, when it is in this primitive state, have
considered that it deserved some special name, wherewith to distinguish
it from all other things, and the cytode®, as it was called, ranked as a sort
of histological Adam.
IGr. iotos, web, tissue ; and Adyos, discourse. Also written Histiology, from
Gr. itoriov, tissue.
2Mikroskopische Untersuchungen, Sydenham Society’s translation, London, 1847,
p. 165.
3From the Greek for cell, xiros; the term cell is derived from the Latin cella,
akin to celare, to hide, conceal, hence a small closed cavity or hollow place.
2 THE CELL THEORY.
But this varying nomenclature came to be only confusing, and the
name cell once more regained its ascendancy. But it was found that as
the history of the lower forms of animal life were studied and revealed,
that they were nothing more nor less than single cells, it was still an open
question what the cellessentially consists of. Hypotheses of their precipita-
tion, and subsequent modification were not wanting toaccount for their exist-
ence. Most observers, however, agreed that the outer part, which is usually
firmer in texture, was not essential, but only the result of development,
and the cell-wall ceased to trouble naturalists. But, within the cell,
there often exists a denser portion, usually of spherical form, and this
nucleus, and its contained nucleolus, were long looked upon by some
observers as the necessary origins of the cell; their conclusions being
based upon the fact, that when nucleated cells multiply they generally
do so by a division through the nucleus, and greater weight was attached
to this, inasmuch as in all previously observed cases of sexual generation
those of the nucleus heralded all subsequent changes. Moreover, amongst
the unicellular animals, known as Jnfusoria, so active do the nucleus and
nucleolus become, that a specialisation of function, the function of repro-
duction by sexual generation, was assigned to them. The importance of
the nucleus to the cell falls to the ground, however, when we come to
consider that there is a legion of forms which do entirely without a
nucleus throughout the whole of their lives, and that, indeed, this dis-
tinction of nucleated and non-nucleated cells has been taken advantage of
in a natural classification of these lowly organisms, which thus admit of
a division into Monera! and Endoplastica.2, Superadded to this there is
the incontestible fact that nucleated cells, even amongst the highest order
of animated beings, often subdivide in their development, independently
of their nuclei.
From what has been stated, it will be clear that all attempts at a
nomenclature which seeks to designate any s*ngle definite thing as a cell,
must of necessity be futile, for the morphological unit varies, not only in
its nature from the very commencement, but in the course of its indi-
vidual development. Thus, the simple mass of undifferentiated protoplasm
known as Protameba, originates as Protameba, and often remains a
fixed type ; but it may change, it may develop a nucleus and contractile
vesicle, and become an Amabla. Ameba itself may reproduce young
Amebe, which do not differ in any way from the parent organism, and
which grow thereafter, but in size only. Other cases commence as
Amebe, but subsequently develop into more complex forms, e.g., Hydra.
/ e . .
1Gr, MOVOS, single, an order of Protozoa, embracing those forms whose bodies
consist of simple undifferentiated protoplasm.
- BY Si is ee
2Gr, evdov, within ; tAaords, formed ; nucleated Protozoa.
STUDIES IN MICROSCOPICAL SCIENCE. 3
Each cell of the adult Hydra assumes a columnar, or rather a cuboid
shape, ig:mucleated, and. spossesses an outer merabranous envelope, some-
times only recognisable as a denser hyaline portion.
Amongst the higher animals, most of the tissues of the hody, save
those of certain glandular organs, are composed of aggregates of nucleated
cells with well-defined cell-walls. . In the course of growth, some of these
cells are cast off from'the economy, as mere cell-walls, their contents have
vanished, and they ‘titir6 loiiger of huiy tise to the body ; ; they exercise a
protective function to the cells beneath them for a time, and are there-
after discarded ; familiar examples of such cells may be seen all over the
general surface of the body ; they may be readily obtained from the region
of the scalp in man, whence their detached elements are known as “ scurf,”
in the external ear, near the roots of the nails, and the transitional or red
portion of the lips they are most noticeably abundant, and can easily be
procured for examination ; in certain local and temporary irritations, such
as chaps and blisters they are sometimes too evidently manifest, and in
chronically diseased conditions, as in psoriasis and scurvy, they are painfully
present.
But there are other cells in the body which also ultimately lose their
nuclei and cell-contents, but, in so doing, accumulate an amount of matter,
in their cell-walls, upon the. passive mechanical properties of which their
physiological functions depend. The enamel fibres of the teeth, in all the
higher animals, afford excellent illustrations here, for they consist entirely
of thickened calcified cell walls of peculiar elongated shapes, apposed to
one another.
In the mucous membranes, all the superficial cells of their secreting
surfaces are of columnar or sub-columnar shapes, and possess nuclei, but
every here and there, one of the cells assumes a globular shape, its upper
rim bursts, and its contents are partially discharged ; by some observers
these goblet-cells are looked upon as unicellular glands, with a mucin
secreting function, by others they are regarded as the degraded equiva-
Jents of the dead scales of the skin noted above, and make room, in
this manner, for the younger cells, which are destined to take their
places.
Yet a little more deeply seated, within the true glands of the body, the
cells are devoid of any distinct envelope, but are possessed of
well-developed protoplasmic bodies of a firm consistency, and are
nucleated.
Other tissues of the highly organised animal body present cells which
are nucleated and possess both protoplasm and cell-walls, yet they lie
imbedded in a substance which it is difficult to account for, and which
would defy the labours of the histologist, unless he studied the growth of
the tissues in question. For instance, the whole group of the connective
tissues present this phenomenon—that their cell-walls are being constantly
produced from the protoplasm within, which divides, and gives
4 THE CELL THEORY.
rise to new cells, which, in their turn, form new cell-walls, until a dohien
stage is arrived at, when farther development ceases. Concurrently with
these changes of growth, the outer moieties of the cell-walls become fused
together to produce a more or less homogeneous intercellular substance,
known as the matrix in hyaline cartilage, whilst the cells themselves retain
their individuality intact, that is, they are possessed of protoplasm, nucleus,
and cell-wall ; the change goes a little further, and the homogeneous-look-
ing matrix becomes fibrillated, in which ease the varieties of tissue, known
as white fibro and yellow fibro cartilage result, the difference being mani-
fested in a preponderance of the gelatigenous element in the former, and
of the elastic element in the latter instance. In every case, however, the
cartilage cells remain of an ovoid form; where they subsequently throw
out processes, and where the matrix becomes highly calcified and the ori-
ginal cell-wall, too, takes up lime salts, the branches, anastomose, and,
finally, the protoplasmic cell processes are withdrawn, the structure known
as bone is the result.
To diverge in yet another direction, the cells may throw out filaments
which anastomose, and form a reticulated structure; at the same time,
they produce a jelly-like material in the interspaces of the reti-
culum, that is known as mucous tissue, and is the transitory
form of embryonal tissue; it obtains permanently in the vitreous
humour of the eye. The foatal mucous tissue develops still further with
the growth of the animal, and the mucous intercellular matrix becomes
fibrillated ; when the celatigenous element is in excess it is called white
fibrous tissue’ ; when the fibres are chiefly composed of the elastic element
it is said to be yellow fibrous tissue. Some of the cells of the connective
tissue withdraw their filamentous processes or may never develop them ;
in this condition they possess the power of locomotion, and are termed
wandering cells ; others remain fixed and immovable, clasping the fibres
which they combined to produce, whilst a third set remain fixed, but
slowly change their form.
There is yet another interesting type of tissue called retiform or
adenoid tissue, which is composed of a dense reticulum organically derived
from the coalescence of branched cells. The network thus produced may
give rise to cells of other shapes by a process analogous to gemmation,
and superadded to all this the interspaces of the reticulum may be filled
with corpuscles derived from quite another source, viz., the lymph.
Adenoid tissue is characteristic of the spleen and lymph glands in general.
Muscular and nervous tissue again, form a departure from the normal
type of the cell in very marked ways. Whilst their cell walls and nuclei
remain but slightly altered except in form, their protoplasmic contents
undergo profound changes, resulting in the case of striated muscle in a
peculiar banded structure, ‘the true nature of which is still involved in
considerable obscurity, owing to the complicated questions which have
arisen from imperfect illumination and the use of the high powers of the
microscope which are required for its elucidation. |
Yet all these diverse forms of elements have been ealled cel/s ; from
the independent little Protamewba, with its apparently structureless jelly-
CELL THEORY. 5
like body, through the passive calcified cell-wall of the enamel fibres of
the teeth, to the complicated cells of striated muscular fibre. No rational
attempt to classify them was made until recently, when RurHEerrorp! did
so in a clear exposition to his students in the University of Edinburgh.
The following is a slight modification of his generalisation :—
A cell may be any one of the three following things :—
1. A protoplast, with or without a periplast.
2. An endoplastic or nucleated protoplast, with or without a peri-
plast.
3.
v/
\ fa
Se 2
= Ad
ee wee
FIBROUS CONNECTIVE TISSUE.
AREOLAR Tissue x 400 Diam.
Etymology.—Areola (dim. of area, a void space). Areolar tissue
is the filmy tissue which largely pervades and connects the different
parts of the organs of the body, hence its name connective tissue. The
older writers called it cellular tissue ignoring its essentially fibrous
character. It is often spoken of as the filamentous tissue.
INTRODUCTION.
Much confusion exists in speaking and writing of areolar tissue on
account of the very numerous terms—many more than we have ien-
tioned—under which it is known. It is a compound of two fibrous
tissues (white fibrous and yellow elastic) enclosing cells and spaces
(areolae).
Klein, in his brilliant little manual,' does much to clear the confusion
by dividing connective tissues into “three great groups ” :—
1. Fibrous connective tissue.
2. Cartilage.
3. Bone.
These he points out have in common a ground substance or matria
together with, but distinguishable from, cells.
In fibrous connective tissue, the matrix yields gelatin: in cartilage it
yields chondrin ; and in bone it is petrified with, and therefore yields ;
inorgani¢ salts. In fibrous connective tissue the cells are called con-
nective tissue cells or connective tissue corpuscles: in cartilage the cells
are called cartilage cells: in bone they are called bone cells.
1Elements of Histology. Cassell & Co.
b©
bo
STUDIES IN MICROSCOPICAL SCIENCE.
White fibrous tissue, its forms and disposal, plus its accompanying
cells or corpuscles, form the greater part of the fibrous connective
tissues including areolar tissue. White fibrous tissue forms rope like
bodies (tendons) which connect muscles with bones. As fasciae (from
the Latin fascia, a bandage) or sheet like expansions, it forms sheaths
for the muscles. It forms also a felt work, by its bundles repeatedly
crossing and dividing. This felt work may be close and compact, as in
the dura mater and sheaths of tendons, or it may be so loose as to allow
areas or void spaces (areole) as seen under any part of the skin. Lastly,
it may form a fenestrated membrane, by its bundles interlacing én the
same plane. We thus see that its forms and disposal may be regarded
as four, namely : 1, Rope-like bodies (tendons) ; 2, Sheet-like
bodies (fasciae) ; 3, Open, or close felt-work ; 4, Fenestrae.
White fibrous tissue in our drawing and accompanying slide is seen
to be composed of bundles of fine fibres running strictly parallel with
each other but taking a wavy course. However the bundles themselves
run, whether parallel to each other, as in tendons and fasciae, or dividing and
re-uniting and crossing each other as in the felt work, or fenestrated
forms, the individual fibres composing the bundles always maintain their
general parallelism to one another. Other peculiarities of these filaments
are that they never divide into branches, or unite with one another. When
seen by reflected light they appear white or nearly so; they, however,
readily transmit light and appear transparent. They are to all appearance
homogeneous, and the same thickness throughout their course, and vary
in diameter from the 50,000 to the 25,000 of aninch. The bundles
formed by the filaments vary much in thickness, some being made up of
very few filaments, never, however, less then three or four, whilst in
others many scores may be seen. The filaments are held together by a
semi-fluid albuminous cement which is also present between the bundles
forming a trabecula. To demonstrate this, tear off a narrow strip of
tendo-Achilles from any quadruped: place it ina saturated solution of
picric acid for forty-eight hours: wash away all coloring matter by
repeatedly changing the water: tear off a small shred and tease it well
out in three-quarter per cent. salt solution, then cover and examine.
The fibrous connective tissue cells or corpuscles, vary much in shape,
which largely depends on their surroundings. In tendons and fasciae
they are flattened squares, or oblongs, placed end to end, situated on the
surface of groups of fibre bundles. Between the ends of the cells is
found the albuminous cement. In mucous membranes, true skin, serous
membranes, cornea, and subcutaneous tissue, the cells are flattened and
branched, branches of one cell joining with those of another, thus forming
intercellular communication.
Yellow elastic tissue is usually associated with the white fibrous tissue
in most places. When seen in bulk as in the ligamentum nucha of large
quadrupeds, such as the horse, ox, &c., it is seen to be yellow in colour,
but when single fibres are seen by transmitted light, as in the slide
AREOLAR TISSUE. 23
accompanying this number, they appear transparent with a well-defined
outline. We can always readily distinguish them from the white fibrous
tissue, which we have seen runs in wavy parallel bundles of filaments; the
fibres of yellow elastic tissue run in bold curves, and the ends of the
fibres curl. Again, we saw that the white filaments never branched, the
yellow fibres branch, and not only so, but the branches join and form a
reticulum. When cut across, the yellow fibres are seen to be angular.
When much white fibre is present, and very little yellow elastic, the
latter is discovered by irrigating the specimen with a one per cent. solu-
tion of acetic acid in water. ‘This causes the white fibrous tissue to
swell up and become indistinct and leaves the yellow fibres alone and
untouched ; it also, by the way, brings the cells into view.
AREOLAR TISSUE.
By our foregoing remarks it will be seen that the practice of describing
areolar tissue as a special variety of a fibrous connective tissue is mis-
leading. It is really a typical connective fibrous tissue, made up of
larger or smaller bundles of white fibrous tissue copiously mixed with
yellow elastic fibres, the two blending with one another to form a felt
work, usually of loose texture. The yellow fibres run in the ground
substance, between the white bundles, and appear very often, as in our
specimen, to run on the surface. The areole or interspaces are clefts,
and freely communicate, being formed by the liquefaction of the ground
substance and development of fibres, and are occupied by the connective
tissue cells or corpuscles.
Except in the eyelids and one other part, the areolar tissue, which lies
beneath the skin in all parts of the body, and is therefore called sub-
cutaneous tissue, contains fat cells. Each cell is formed of a capsule of
protoplasm, having at one part of its periphery a more or less flattened
nucleus, and encloses a globule of oil. These fat cells are formed by
the conversion of the original connective tissue corpuscle. When men
and animals “grow fat,” it is this conversion of the subcutaneous con-
nective tissue corpuscles into fat cells which gives the body its rotundity.
In starving animals the oil gets absorbed, and the fat cell diminishes,
and contains only a serous fluid, which itself disappears as starvation
proceeds. It is thus seen that the areolar tissue beneath the skin is the
great store house of the body. The fat is stored up in it in good times,
to be called upon by the body’s needs in time of want.
Areolar tissue next after the blood is the most universally distributed
of the tissues. As we have said, it lies beneath the skin everywhere,
also beneath the serous and mucous membranes, attaching them to the
parts which they cover or invest. It pervades and also invests the
different organs, such as muscles, nerves, blood-vessels, lobes, and lobules
of compound glands, the hollow viscera, such as the bowels, etc. Itis not
24 STUDIES IN MICROSCOPICAL SCIENCE.
only universally distributed, but is continuous with itself throughout. It.
is through the areole of this tissue that our medicines, injected beneath the
skin anywhere, get into the blood instantly and over the whole system ;
it isin this that dropsy lodges, and freely shifts its quarters from ankles to
eyelids and face, or any other part, often depending upon position only.
In the days before the legal protection of animals from cruelty, the
butcher whitened his veal by bleeding the calf almost to faintness a day
or two before killing it, and after piercing the skin, inserted his tobacco
pipe stem, and inflated the entire skin by blowing into the areolar tissue.
Should a quadruped have an abscess form and discharge, or receive a cut
through the skin over the breast between the fore legs, the action of the
large pectoral muscles suffices to suck in air, and the entire skin is puffed
up by the air being drawn into the areole of the subcutaneous tissue.
It is thus seen that the areolar tissue is our store-house of fat: it re-
ceives watery deposits from the blood-vessels: it acts as a convenient
receptacle for medicaments, whether injected beneath the skin. with
a syringe, or rubbed into the skin by inunction: it enables the skin to
move freely over the subjacent parts, and retracts the skin when the latter
is drawn away, and makes the cut skin gape by drawing its cut edges
apart, for which we do not thank it. Its other kindly (and unkindly)
offices, are really ‘‘ too numerous to mention.”
Mopt oF PREPARATION.
For studying areolar tissue, snip out a minute piece of the sub-
cutaneous tissue from a newly-killed quadruped: place it quickly on a
dry slip, and spread it out with needles, breathing upon .it from time to
time to prevent-it drying, then place on it normal salt solution, cover, and
examine.
For a permanent specimen, inject the axilla of a newly-killed kitten
or young rat, witha 1°/, solution of osmic acid. When a bulla has
formed, snip out the areolar tissue, avoiding hairs, place it on a slip as be-
fore, and put on it a large drop of picro carmine, frequently renewed
through 24 hours ; then replace this with glycerine jelly and cover. Log-
wood may be used in place of picro carmine; also glycerine may be
passed under the cover glass, instead of using the glycerine jelly.
BIBLIOGRAPHY.
Klein's Elements of Histology, Cassell and Co.
Harris and Power’s Manual for the Physiological Laboratory, Balliere and Co.
Quain’s Anatomy, vol. ii., 9th Edition, Longmans.
Sterling’s Practical Histology, Smith, Elder, and Co.
Stel Llate 7.
"Stele del ad nat TW Watson dad. rt lth
TENDON OF LAMB
xX 70
Watson. & Son lith. 93 ( Charles St Burm
FIBROUS CONNECTIVE TISSUE.
( Continued.)
Tendon T.S. x diam.
Etymology.—(révwv, a tendon, from refvw, I stretch). A fibrous
cord at the extremity of a muscle by whicha muscle is connected with a
bone. Tendons are white and glistening, and vary in length and thick-
ness: they are sometimes round, sumetimes flattened: they are of con-
siderable strength, with very little elasticity.
DESCRIPTION.
Tendons consist almost entirely of white fibrous tissue, the fibrils of
which have an undulating course parallel with each other, and are firmly
united together. The bundles of fibres do not keep separate throughout
their length, but send slips to neighbouring bundles, and receive slips
from neighbouring bundles in return ; hence, successive transverse sec-
tions of the same tendon reveal different figures of the sectional areas of
the bundles. On referring to the present slide, it will be observed that
the bundles are not only invested by dense areolar tissne, but trabeculae
are sent from this into the interior, forming septae of greater or less
thickness, thus uniting all the bundles of fibres into one large collec-
tion of fibres. Besides binding the bundles together, these septae of
areolar tissue serve as an imbedding and protecting agent for the
vessels and nerves, which, however, are very sparingly supplied, and
of small size, running for the most part in the larger trabeculae and
sending communicating branches across them, and then forming an open
network with large oblong meshes. If tendons seem to lack blood
vessels, they at all events are richly supplied with lymphatic vessels
which penetrate both the large and small trabeculae of the areolar tissue.
The present slide exhibits these in numerous places transmitting light
from the mirror as if they were so many pin holes. Their areolar
character of is shown by their irregular outline, also by the fibres
running across each at a lower level. The tendon cells are seen in
section as irregularly stellate. They are stained, and give each bundle
of fibres a dotted appearance, as seen with a low power such as an inch.
The tendon cell consists of a protoplasmic body, thick at the centre, and
thinning off into extensions, hence its stellate form. When seen ina
longitudinal section of a tendon they appear quadrangular or oblong.» As
the body of the cell lies between the angular space between three or more
bundles of fibres its lamellar processes extend into the interstices between
these contiguous bundles. It will thus readily be seen that the oblong
form of the cells as viewed from the side is quite consistent with their
STUDIES IN MICROSCOPICAL SCIENCE.
bo
(or)
——
being stellate when viewed in transverse section, the bodies of course are
flattened as well as the extensions or processes, but not so much so,
When viewed in longitudinal section, the cells are seen to form a ribbon
shape, with slight interspaces between each cell, their nuclei being at
the end of the cell, those of every two cells being as close together as
possible. Another peculiarity of the longitudinal section of the tendon
with its cells im situ is the appearance of the attenuated processes : these
appear as well-defined dark lines, usually two in number, which are
seen in the same focus as the cell nucleus.
When a muscle ends in a tendon, the muscle fibres either run in the
same direction as tendon bundles, or join the tendon at an acute angle.
The fibres of each tendon-bundle end a on reaching the rounded
or obliquely truncated extremity of a muscular fibre, and are so intimately
united to the prolongation of sarcolemma, which covers the extremity, as
to render the separation difficult to detect. Ranvimr.
Mops oF PREPARATION,
There are four structures or elements to be observed in tendon,
namely :—
Areolar tissue investment.
Ground substance or matrix.
Fibres.
Cells.
Vessels and nerves.
It is obvious that we require more preparations than one, to. exhibit
the peculiarities of each. For instance, we have seen that the cells, viewed
lengthwise, have an oblong appearance, but, when cut across, are irregu-
larly stellate, therefore, either a transverse section, or a longitudinal one,
would, by itself, be insufficient for the cells. Two sections, and one
teased preparation, are needed, to show everything that can be made
out.
Ground substance or matriz.—On page 22, of the last number,
this has been described, and a description of the process for seeing
it.
Fibres.—The tendo achilles of a calf is taken, and an inch or so of its
length cut out. This is to be again cut longitudinally into three or four
pieces. Place the pieces fora fortnight in Miiller’s fluid, then wash away
all the colouring matter by frequent changes of water, and transfer to
50, afterwards to 70 per cent., alcohol. Longitudinal sections of this
cut very thin, stained in picro carmine, and mounted in Farrant’s
medium, will shew the fibres very well.
Cells.—Take the tail of a new-born rat or mouse, nip the end of it,
and draw out a leash of tendons ; place these for five minutes in filtered
juice of afresh lemon. They clear up, swell, and become transparent.
Now wash them in distilled water and transfer them to one per cent. solution
TENDON. oT
of auric chloride for twenty minutes, and after they have assumed a deep
yellow tint, again wash them in distilled water, and transfer them to
an ounce of 25 p.c. solution of Formic Acid. Place in the dark, in a
cool place, for twenty-four hours. Again washin water. They are now
purple throughout. Take a small piece of one of them, and tease it out
with needles, in a drop of glycerine, and cover. The cover glass may be
used in place of the needles, by squeezing and flattening out the pre-
paration. This shews the relation of the cells and fibres.
Again, take the tail of a rat, and treat it with auric chloride, as in the
last case. Now transfer it to chromic and nitric fluid to decalcify.
Make transverse and longitudinal sections: stain these in lodine green
and in aniline blue—at least in the former—then mount in benzole
balsam.
Areolar-tissue.— This is well seen in the transverse section of the rat’s
tail as above.
Vessels.—These may be injected with a carmine mass in the rat, if
desired, though it is scarcely worth while, as the vessels are quite un-
mistakable without injection.
Relation of Muscle to Tendon.—Cut out the diaphragm of a newly-
killed rabbit : place it in filtered fresh lemon juice for five minutes: then
steep it in 1 p.c. aqueous solution of auric chloride for one hour, and
transfer to 25 p.c. solution of Formic acid 24 hours, the preparation to
be kept in a dark, cool place during the latter period. Snip out a piece
of muscle with central tendon attached, and tease in glycerine. It is
better perhaps to place the whole in gum and syrup (see Methods of
Microscopical Research), then freeze and cut. The section is to be
parallel with the long axis of the muscle fibres.
BIBLIOGRAPHY.
Ranvier, in Arch. de Physiol., 1869 and 1874.
Citerbock, in Med. Centralbl., 1870.
Mitchell Bruce, in Qu. Jr. Micro. Sci. xii., 1872.
Ciaccio, in Mem. d. Accad. d. Bologna, 1872.
Ponfick, in Med. Centralbl., 1872.
Bizzozro, in Molesch. Unters., 1872.
Spina, in Wiener Med, Jahrb., 1873 and 1875.
Griinhagen, in Arch. f. mikr. Anat., ix., 1873.
Stefanini, S. Strutt. d. tess. tend., 1874.
Herzog, in Zeitschr. f. Anat. u. Entw., 1875.
Key and Retzius, in Nord. Med. Ark 1875.
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ADIPOSE TISSUE
X 250
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ADIPOSE TISSUE.
x 250 diameters.
Etymology.—The word adipose is from the latin adeps, adipis, fat.
FATS.
These substances, like the sugars, are derived from both animal and
vegetable sources. There are three principal varieties of them, which
may be considered as representing the class, viz. :
Oleine - = Cy He, 0;
Margarine - AOE G Al ik 5 A Oe
Stearine - ei Wass eda OW;
The principal difference between the oleaginous and saccharine sub-
stances, so far as regards their ultimate composition, is that in the sugars
the oxygen and hydrogen always exist together in the proportion to form
water ; while in the fats the proportion of carbon and hydrogen are nearly
the same, but that of oxygen is considerably less. The fats are all fluid
at a high temperature, but assume the solid form on cooling. Their melt-
ing points vary very much, and are :—
Stearine, 143° Fahr.
Margarine, 118" ,,
Oleine, LOOP and és:
The fats are all insoluble in water, but readily soluble in ether. By
prolonged boiling in water with a caustic alkali, they are decomposed,
and as the result of the decomposition there are formed two new bodies ;
first, Glycerine, which is a colourless, neutral fluid: and, secondly, a
fatty acid either oleic, margaric, or stearic, as the case may be. The gly-
cerine remains in a free state, whilst the acid wnztes with the alkali to
form a soap.
Stearine is best obtained from beef or mutton suet. Itis the hardest
of the fats, and crystallises in white shining plates. ,
Margarine (papyapis, a pearl), or mother-of-pearl fat, is a constituent of
all oils, hardening rapidly and assuming a crystalline form which glitters
like mother-of-pearl.
30 STUDIES IN MICROSCOPICAL SCIENCE.
Oleine may be obtained best from olive oil. Stearine, margarine, and
oleine never occur separately : in every fatty substance they are mingled
together, so that the more fluid of them hold in solution the more solid.
Generally speaking, in the living body these mixtures are nearly fluid.
After death, as the body cools, the stearine and margarine sometimes
separate from the mixtute in a crystalline form, since the oleitie can no
longer hold in solution so large a quantity of them as it was capable of
doing during a life temperature.
Ina fluid state fatty substances present themselves under the form of
drops or globules, which vary greatly in size but always assume the same
optical properties. They are circular in shape and have a faint amber
colour, distinct in the larger globules, less so in the smaller. They have
a sharp, well defined outline, and refract light strongly, and act like
double convex lenses, and therefore appear with ngs centres surrounded
by darker borders.
Pereira gives the following per centage of oily matter in some animal
and vegetable foods :—
Quantity of fat in 100 parts.
Wilberts + te 60:00 Ordinary meat... 14:30
Walnuts) fs. 3.,800°00 Liver, of o@ ue 3°89
COCOS-MuUbeae ashes 47-00 Cow's milk’. ae 31D
Olives’ Hier 32°00 Human milk...... owe
Lanseed 22 ee! 22 00 Ass’s' milk)... 0-11.
Indian Corn) ia 9:00 Goat’s milk '...3 3°32
Yolk of Eggs ... 28:00
Fats or oils can easily be extracted from organised tissues by the employ-
ment of simple mechanical means, because the three principal varieties
of oleaginous matter, though always united with each other,
are not united with the other proximate principles. Thus,
suppose we wish to extract the suyars of the blood, we should
find them in solution in water in company with albumen, phosphate of
lime, chloride of sodium, and the like in molecular union. On the other
hand, we may remove the yolk of an egg en masse, churn the fat from
the milks, cut animal or vegetable tissue into small pieces, and subject it
to heat and pressure, and the oil is forced out and separated. The oils
are found in the animal body most abundantly in the adipose tissue
though they exist in smaller amount in the mammary gland as milk,
chyle, in the liver cells, etc. A large part of the fat, in what-
ever form, may be accounted for by that taken with the food,
animal or vegetable, but it would seem, from the | experiments
of MM. Dumas and Milne-Edwards on bees,' M. Persoz on geese,” and
M. Boussingault on geese, ducks, and pigs,° that fat is formed in the
) Annales de Chim. et de phys., 3d Series, vol. xiv., p. 400.
“Tbid., p. 408.
3Chim. Agricole, Paris, 1854.
ADIPOSE TISSUE. ok
body independently of what is introduced with the food. The observers
first ascertained the quantity of fat existing in the whole body at the
commencement of the experiment. The animals were then subjected to
a definite nutritious regimen, in which the quantity of fatty matter was
duly ascertained by analysis. The experiments lasted variously from
thirty-one days to eight months, then the animals were killed and
examined. The results showed that considerably more fat had accumu-
lated in the tissues than could be accounted for by the fat of the food
taken, which placed beyond doubt that the system can form fat by the
metamorphosis of other proximate principles.
Although the food taken as fat, may produce most fat, other sub-
stances produce fat in abundance. In sugar-growing countries, such as
Louisiana and the West Indies, during the few weeks occupied in
gathering the cane and extracting the sugar, all the negroes employed on
the plantation, and even the horses and cattle, that are allowed to feed
freely on the saccharine juices, grow fat, and lose their superabundance
of fat when the season is past.
ADIPOSE TISSUE.
As we have said, by far the greater part of the fat of the body, is en-
closed in small cells or vesicles, which, together with their contained
matter, constitute adipose tissue.
When seen under the microscope, the tissue is found to consist of
small vesicles filled with oily matter and mostly lodged in the meshes of
areolar tissue. ‘‘ The vesicles are most commonly collected into little
lobular clusters, and these again into the little lumps of fat which we see
with the naked eye, and which in some parts are aggregated into round
or irregular masses of considerable magnitude. Sometimes the vesicles,
though grouped together, have less of a clustered arrangement ; as when
they collect alongside of the minute blood-vessels of thin membranous
parts. In well nourished bodies the vesicles or fat cells are round or
oval unless they are packed closely together, in which case they acquire
an angular figure, and bear a striking resemblance to the cells of vegetable
tissues. The greater number of them are from the stv to the sv of an
inch in diamater, but may exceed or fall short of this measurement.
Each one consists of a very delicate envelope enclosing the oily
matter, which, completely filling the envelope, appears as a
single drop. It often happens that a part of the fatty
contents solidifies in the cell after death, forming a_ bunch
of delicate needle-shaped crystals. The envelope is the remains
of the original protoplasm of the cell: it is generally quite trans-
parent, and apparently homogeneous. According to some authorities it
consists of two parts: a delicate structureless external membrane, and a
layer of finely granular protoplasm immediately surrounding the fat. The
32 STUDIES IN MICROSCOPICAL SCIENCE.
nucleus is always present in the protoplasm, but is often so flattened out
by the pressure of the enclosed oil-drop as to be visible only with diffi- -
culty. The areolar tissue connects and surrounds the larger lumps of fat,
but forms no special envelope to the smaller clusters ; and although fine
fasciculi and filaments of that tissue pass irregularly over and through the
clusters, yet it is probable that the vesicles are held together in these ©
eroups mainly by the fine network of capillary vessels distributed to
ihem. In the marrow the connective tissue fibrils are but few
in number or may, it 1s said, be absent altogether. The adipose tissue
is copiously supplied with blood-vessels. The larger branches of these
pass into the fat lumps, where they run between the lobules and sub-
divide till at length a little artery and vein are sent to each lobule,
dividing into a network of capillaries, which passes between the vesicles
in all directions, supporting and connecting them. The lymphatics of
the fat are in close relation to the blood-vessels, accompanying and oc-
casionally completely enclosing them as they enter the lobule. No
nerves have been seen to terminate in this tissue, although nerves,
destined to other tissues, pass through it.” (Quain.)
MertHop oF PREPARATION.
Our section with this number is from the subcutaneous tissue of the
palm of the hand. It is cut by the imbedding process, and stained with
strong logwood solution and mounted in glycerine jelly.
BIBLIOGRAPHY.
All works on anatomy may be consulted, as all treat on adipose tissue
with greater or less lucidity. In the 9th edition of Quatn vol. ii. p. 73,
74, 75, will be found a good description, from which we have made a
large extract. Works on Physiology also have a good deal to say about
the fats, etc., so have works on Chemistry. 4
Plate J
See L
SU Watson del hits
OSSIFICATION OF CARTILAGE
(Quai)
X 300
Watson &Son lilh 93. 6+ Charles S¢ Burm .
DEVELOPMENT OF BONE.
Section x 350 diam.
Etymology.—Several terms used in discussing bone formation
require to be explained or known in advance. The following words
occur: the prefix oste from the Greek ooreov (a bone). Osteoblast from
the Greek Bkacros (a bud, a shoot, a sucker). Osteogenetic from the
Greek yevvaw (to produce, to bring forth). The prefix os from the Latin
os (a bone). The prefix calc from the Latin calx (lime). Diaphysis and
Epiphysis are the same word with different prefixes. They are from
the Greek vw to spring forth or come into being hence diadvw to
intervene : exupvw to grow upon, to cling closely to.
INTRODUCTION.
In order to understand the development of bone, we first propose to
explain what bone is when fully formed, as we find it in the full-grown
healthy animal ; then we have to begin quite at the other end and trace
the process from the primitive structures as we find them, not only in
the foetus but in the young or very early foetus ; thus, we count an
animal’s age from its birth, but before birth we count its age as a foetus.
We again have to allow for differences in foetal development; thus a
foetus which is mature and ready to be born, so to speak, at six weeks
old is mature and formed at that time and almost so at four weeks,
whereas a foetus that is only fit for a separate existence at twelve months
is very imperfectly formed at four weeks. Therefore when we speak of
an early foetus or young foetus, we must be understood to mean an early
or young foetus of the animal which bears it, and then consider how long
that animal carries its young before birth.
When bone is fully formed it consists of an organic framework im-
pregnated with lime and other earths, which make it rigid.
Lehman gives the following proportions :—
Organic matter... a ... oo per cent,
Earthy matter... vs pee Oh ehh 55
The earthy matter is almost all lime and is made up of 57 parts of the
phosphate and 8 parts of the carbonate of lime: the only two remaining
earthy parts are one part each of fluoride of. calcium and phosphate of
magnesia. Practically, then, we find bone to be made of an organic
base, impregnated with lime, which has been named “bone earth.” If
54 STUDIES IN MICROSCOPICAL SCIENCE. ]
”
we soak an adult healthy bone in water, which contains one or two per
cent. of hydrochloric acid, we can, in a few days, run a needle through
it, without the needle encountering any resistance from grit, and if it
be a long bone we can almost tie it in a knot: it still looks
like a bone, however. Again, if we put an adult healthy bone in a
very hot fire in a few hours we may remove it, and it still
retains its shape, but is whiter. We now can pinch a piece from it, and
powder the piece between our fingers: the animal basis has gone, and
left the lime only. If we saw a long healthy adult bone down its middle
lengthwise, we find it made up of two distinct parts: am outer compact
tissue, and an inner open or cancellous tissue. ‘These form the outer
ease or shaft, and enclose a hollow space, which gives it lightness and
strength, because the amount of material being the same, a hollow cylin-
der is stronger than a solid pillar. This hollow also contains the mar-
row. If again, we fracture a fresh adult healthy bone, that has been
cleared of its muscles and not scraped, a tough membrane will still
hold the fragments together. This membrane is the periosteum, and
invests the bone everywhere, except at the insertion of strong tendons,
and where it is covered by cartilage. The periosteum is a tough fibrous
membrane, whose chief use is as a bed in which the blood vessels divide
and subdivide, until they are fine enough to enter the minute pores
which are to be seen on the surface of a dried bone that has been macer-
ated and deprived of its periosteum.
A healthy adult long bone of a mammal, such as the thigh bone of a
man, horse, sheep, is anatomically divided into a shaft and two extremi-
ties. Again we find enlargements on this bone, as on other bones going
under various names, such as trochanters, tuberosities, and so forth.
The parts of the embryo destined to become bone first appear in the
early foetus as a gelatinous pulp, without a trace of organisation, and
contained in a delicate membrane. This pulp gradually organises
and appears as hyaline cartilage, such as it is in a permanent
form. This we have illustrated and described in a_ previous
number. The entire skeleton, except the skull cap and bones of the
face is first of all in the early foetus hyaline cartilage. The bones which
are to form the skull cap or cranial vanlt and the bones of the face are
not so much as represented in the early foetus as hyaline cartilage, but
by two closely apposed delicate membranes which in the case of the
cranial vault become respectively the peri-cranium and the dura-mater.
Between these two closely apposed membranes, bone is developed. There-
fore it 1s usual to describe bone as'developed by two modes of ossification,
namely :—
1. Ossification in Cartilage.
2. i ,, Membrane.
The former method only is exhibited by our present slide and drawing,
and the very early and very late phases of this are not shewn. Those
who wish to trace the process throughout can do so by the directions we
shall give.
DEVELOPMENT OF BONE. 35
DEVELOPMENT OF Bones.
1. Ossification in Cartilage.—We will take the femur or thigh bone
as our type. All parts of this or any other bone do not become
ossified together, nor do all bones of the same skeleton ossify during the
same period of time. Those bones ossify first, which are wanted first.
Thus in the human being the ribs are wanted in the act of breathing,
and the lower jaw is wanted in the act of sucking at birth; therefore, these
are among the earliest of the foetal skeleton to commence to ossify. On
the other hand, some bones or parts of bones are not required for so long
after birth that they do not commence to ossify till, in some cases, years
thereafter.
The process of ossification in cartilage commences in the centre of the
cartilage, therefore these spots are called centres of ossification. When
a cartilage, forming the bone that is to be, begins to ossify, the part of it
which is first to ossify has first of alla mere speck in its centre. This
speck is seen to consist of minute canals for the passage of the blood
vessels. Presently we see blood vessels in these canals. What are
these blood-vessels doing? Blood at this early stage, as it is throughout
life, is the great carting or carrying agent; it carries materials to build
up the tissues through which the vessels pass, and receives from the
tissues the cast off worn out material. In the present case, the blood
is carrying “‘ bone earth ” in solution, to the parts, and earrying away the
broken-down cartilage which the bone proper is supplanting, hence there
is in the ossifying centre no redundancy of bulk.
The number of these centres varies in different bones, some have only
one, others half-a-dozen or more, the humun sacrum has as many as
thirty-three. In the human femur the first centre of ossification (that
in the middle of the shaft) appears in the beginning of the third month
of fetul life. The second centre appears during the last month of fetal
life at the lower extremity which forms part of the knee. The third
centre appears at the upper extremity when the child is a year old. In
the fourth year of childhood the fourth centre forms in the large pro-
minence (trochanter major) at the upper extremity of the bone. The
fifth and last centre does not appear until the child has become a youth
of fourteen or fifteen.
The shaft is the first part to ossify, as is the case in all the long bones,
and for this reason we speak of it as the diaphysis (the part that
intervenes), the other parts growing upon the shaft, so to speak, we call
epiphyses. The epiphyses, during all this long period of growth, are only
united to the shaft by a layer of cartilage, hence the frequency of the dis-
placement of these epiphyses in childhood and early life of the mammal
generally.
The slide and drawing ought now to be intelligible. The end of a
long bone is shown. This is seen to consist of two distinct parts in the
section :—
1. The end of the shaft.
2. The head of the bone.
36 STUDIES IN MICROSCOPICAL SCIENCE.
The process of ossification commences, as we have said, in the centre of
the ossifying part, and proceeds from the centre, in the case of the long
bones, from the centre to the extremities, and in the irregular bones, or the
irregular parts or epiphyses of along bone, from the centre to the periphery.
Hence in our present section we see ossification at work in two parts, first
it is seen in the piece of the end of the shaft proceeding in a looped
manner, the loops lying lengthwise in the long axis of the piece of the
end of the shaft ; second, it is seen in the centre of the half sphere or
head of the bone. In both cases the fragile open network of new bone
will in places have dropped out in process of cutting and mounting. The
osteoblasts are stained red, and amongst these cells may be found here.
and there giant cells or osteoclasts. The trabecule are stained blue, and
are calcified cartilage matrix in process of becoming covered with se-
condary osseous substance deposited by the osteoblasts. Being taken
from an animal that uses its limbs early, the process of ossification in the
shaft and head of the bone is going on synchronously. “The young
lamb or foal can stand on its four legs as soon as it is born ; it lifts its
body well above the ground, and quickly begins to run and bound. The
shock to the limbs themselves is broken and diminished at this tender
age by the division of the supporting long bones, by the interposition of
the cushions of cartilage between the diaphyses and the epiphyses.”
(Owen).
2. Ossification of Membrane.—For observing this a very young foetus
must be procured. Quain’s Anatomy gives a figure (p. 102, fig. 100,
vol. ii., Hd. ix.) of Sharpey’s. It is the parietal bone ofa foetal sheep, the
latter being only two and a half inches in length. The bone is about half
an inch square. Should the reader desire to study ossification in
membrane, a very young foetus of a rabbit, cat, dog, or guinea pig, may be
procured, stained first in carmine, then in sulph-indigotate of soda, and
then'cleared and mounted in balsam, He will then find a brief bub clear
description as above. It is obvious that adescription here would be of
little use without a slide or a drawing.
_—_—
MoprE oF PREPARATION.
A new born puppy, kitten, guinea-pig, or rabbit is to be procured and
its thigh or arm bones, or both, placed in a saturated watery solution of -
picric acid till a needle can be run through the bone easily and meet no
grit. Then the acid is washed out with water and the bones placed in
methylated spirit for a few days. Sections are then cut with a razor, the
bone being imbedded in carrot. The sections are first stained in carmine,
then in sulph-indigotate of soda (the process having been described in
the Studies once or twice before, we need not trouble the reader with a
repetition), and afterwards mounted in benzole balsam.
BIBLIOGRAPHY.
Any work on Anatomy may be chosen, but the second volume of the ninth edition
of Quain (Longmans & Co.) is the best.
SOLU L_ Plate 10
E[D tal ad nat. ZW Wetvon del o¢ Lath,
TAS ONE RV te aOreHORS Ee
X 150
Watson & Gon Ith 93. 6 Charles S¢ Garm
NERVE OF HORSE.
T.S. x 150 diam.
Etymology.—A ferent and efferent, from the Latin Fero, I bear: ad, to:
ef, from. Neuroglia, from the Greek neuron, a string, a cord, and gloia,
glue, or glovos, anything. sticky. Epineurium from epi, upon, etc. Per?-
neurium from peri, around, about. Hndoneuriwm, from endon, within,
Latin intus. Neurilemma froth lemmu, a husk, a peel, a scale, something
peeled off. All the latter are from the Greek.
Tue Nervous SYSTEM.
Before describing any part of the nervous system, it may be as well to
briefly describe the nervous system as a whole.
The nervous system, for descriptive purposes, may be regarded as com-
posed of three parts, namely :—
Terminals, which receive impressions.
Transmitters, which convey these impressions.
Interpreters, which analyse and dispose of these impressions.
It will now be convenient to take these in the reverse order.
The brain and spinal cord are the great interpreting masses, but
besides these there are numerous little masses called gangha, which we
may leave out of count in our description.
The nerves are the conveyors of impressions from the terminals or
receivers to the brain and spinal cord. In other words, the nerves con-
nect the two extremities.
The terminals vary greatly in form but are really -varieties of the same
thing. The agent or medium by which these terminals communicate the
impressions received, and make an impression of it suitable for trans-
ference differs in each case. Take for example two of the five senses and
their terminals: we have refracting media for modifying beams of light,
and rendering these beams suitable for being received by the retina and
transmitted by the optic nerve: we have a sound modifying apparatus for
modifying sound waves before these are capable of being transmitted
along the auditory nerves, and so forth. In the former case, we have an
optical apparatus, and in the latter an acoustic set of apparatus, and these
instruments of the terminals differ fundamentally.
If we disconnect the instruments of the terminals from the nervous
system proper, we find it to be composed of two structural elements only.
1. Nerve cells.
2. Nerve fibres.
The nerve cells are much fewer in number than the fibres, for this reason :
every nerve fibre commences, or terminates, in a nerve cell; but the
38 STUDIES IN MICROSCOPICAL SCIENCE.
nerve cells are made up of a body which branches. Sometimes these
branches are very numerous, and each branch is continued as a nerve
fibre, or has a nerve fibre running into it. We have said the fibres
commence, or terminate, in nerve cells. This leads us to remark that
nerve fibres convey impressions to and from the nerve centres.
Those fibres which convey impressions from the end organs, or terminals,
to the centres (brain and spinal cord) are called afferent or centripetal :
those which carry the brain or spinal cord explosions or stimuli to the
end organs, or terminals, are termed efferent or centrifugal.
By the unaided eye we can see that the nervous substance is divided
into two kinds, differing in colour, These are :—
1. The white,
2. . The grey, or cineritious.
The white part of the brain and spinal cord is very distinct from the
grey, and is made up of nerve fibres. The grey or cineritious matter is
formed largely of nerve cells. It exists on the surface of the brain and
in the interior of the spinal cord, |
NERVE FIBRES.
We must be careful to remember the difference between nerves and
nerve fibres. When we speak of a nerve, we refer to a number of nerve
fibres, which run in company as a cord or nerve. It is usual to speak
of two kinds of nerve fibres, the white and the grey ; but a white fibre
is made up of a central axis of grey matter, which runs uninterruptedly
from a cell process to its destination, and is surrounded, or coated over,
with a thick white fatty coat called the medullary sheath, and this,
again, is enclosed in a thin membrane or sheath. In other words, a
white nerve fibre is made up of three distinct parts :—1, a central axis of
grey matter; 2, a thick white fatty sheath ; and 3, an envelope, or thin
membrane, which encloses the whole. On the other hand, a grey nerve
fibre has the central axis of grey matter almost exactly like that of the
white nerve fibre, but running along, just as grey matter, and not sur-
rounded, or coated, by anything.
NERVE CELLS.
A nerve cell, like any other cell, consists of a nucleated mass of proto-
plasm having from one to twenty or more processes: hence we speak of
uni-, bi-, or multi-polar nerve cells. The shape of the cell is characteristic
of its locality. The round cell belongs to the spinal ganglia: the angular to
the sympathetic ganglia : the irregular branching cells to the grey matter
of the spinal cord : the conical to the surface of the brain: the flask or
retort shape to the cerebellum, etc. The stze of the nerve cell varies
creatly. The multi-polar nerve cells in the spinal cord are so large that
one can almost see them with the unaided eye, whilst those in a part of
the cerebellum are so small that the layer they form is called the granular
layer. .
Like all other parts of the animai economy, the essential parts of the
nervous system (nerve cells and fibres) require mechanical support :
THE NERVOUS SYSTEM. 39
require blood vessels, nerves, and lymphatics for their nourishment and
continued existence during their wear and tear,
Without physical support, the delicate grey matter would be crushed
or torn, especially in the large collections of nervous substance (brain
and spinal cord). The physical support of the nerve cells and
fibres of the brain and cord is called newroglia. It consists of an
extremely fine, delicate, open net-work, whose _ structure has
not been thoroughly agreed upon. Professor Schafer, in the second
volume of Quain’s anatomy, p. 149, says:— ‘It is not composed
of cells, although these occur in it, but it is rather of the nature of
an intercellular substance which occupies the interstices between the
nerve fibres. The cells which are here and there found in it are flattened,
and resemble small connective tissue corpuscles, and the neuroglia of the
nerve centres has generally been regarded as consisting of connective
tissue ground substance, ere since In many places it appears
fibrillated.”
TRANSVERSE SECTION OF A NERVE.
The transverse section of a nerve, such as accompanies the present de-
scription, shows the following structure.
We have one, two, or .more nerve bundles of different sizes,
mechanically supported and held together by a fibrous arrangement of
areolar tissue. The latter tissue also affords mechanical support to the
nerves, arteries, veins, and lymphatics which must accompany the nerve
trunk as a whole, and afford it proper nourishment.
The sheath which surrounds all the round bundles of fibres is that
which we first come across in dissecting a nerve as it lies in the body,
and is called epineurium. JBesides this each nerve bundle has:a special
sheath for itself, also readily seen: this is called the neurilemma, and is
lamellar in structure, whilst the epineurium znterlaces with itself in all
directions. The neurilemma receives fibres on its outer periphery from
the surrounding epineurium: it also gives off flattened prolongations from
its internal periphery, which go to form septa between the groups of
nerve fibres which compose a single nerve bundle. From these septa
again there is still a smaller structure given off, which separates the indi-
vidual fibres of which a group is composed. This is called the endo-
neurlum. This endoneurium also supports the capillary blood vessels
which nourish the nerve fibres.
Mopgs oF PREPARATION.
To prepare a Nerve.—NDissect out a piece of the sciatic nerve of
horse, ox, dog, or cat. The piece should be an inch long and gently
stretched upon a piece of wood, or a match, and tied at both ends to pre-
vent shrinking if taken from a small animal, If a large animal be
chosen the nerve trunk must be cut lower down where it is smaller.
Place the cut piece for ten days in Miiller’s Fluid. Then transfer to
alcohol as usual. Transverse sections, stained, then cleared and mounted
in balsam, shew the parts we have mentioned in their relative order.
40 STUDIES IN MICROSCOPICAL SCIENCE.
Sections cut longitudinally should also be made. Although the nerve
fibres themselves do not coalesce, the minute bundles which go to form a
nerve bundle both give and receive fibres from neighbouring bundles.
To prepare a Nerve Bundle.—Take a mouse just killed ; make an inci-
sion through the skin in the middle line along the breast bone, and tear
away the skin right and left. Very fine lateral branches will be seen
stretching from the flesh of the chest to the skin, more or less surrounded
by areolar tissue. Pour over the entire parts so exposed a half per cent.
solution of nitrate of silver: then after five minutes cut out little lengths
of these minute nerve trunks and wash them in two or three lots of dis-
tilled water ina watch glass. After the light has changed them toa
faint grey colour, mount them in glycerine jelly. We then can see the
nerve fibres in the form of a bundle, and this bundle coated by a single
layer of epithelium. The intercellular substance of the epithelia is dar-
kened by the silver, and we have silver lines well defined. Here and
there we see beneath ‘this epithelial mail little crosses which we shall de-
scribe Jower down. _
To prepare Single Nerve Fibres.—We have seen that the rdadiiilated
nerve fibres have a coat of fat over the central grey band or axis. As
osmic acid blackens fat we use it to distinguish this thickest, largest
part of a nerve fibre. Kill a frog and dissect out a piece of the sciatic
nerve an inch long. Tie it lightly but firmly to a match with a piece of
fine thread, wetting it with distilled water all the time to prevent it
drying. After cutting it away place it, match and all, in a 1
per cent. solution of osmic acid for ten minutes. Remove it and
wash away all the osmic acid with distilled water, then
place the whole in a test tube and cover it with a solution
of picro-carmine, and gently secure the end of the tube with acork. Let
it remain a fortnight (Stirling), and cut away lengths of one-eighth of an
inch, and dissociate the fibres with needles by means of a “dissecting
microscope. After separating or isolating a few individual fibres, mount
these in glycerine jelly. We now see the three components of the nerve
—the axis cylinder in the centre, the large fatty (medullary) sheath
stained black with the osmic acid, and the whole enveloped in a sheath.
We now notice that the axis cylinder is an unbroken, continuous strand ;
so is the outermost sheath, but this sheath forms constrictions now and
again, und in doing so constricts everything except the central axis ;
therefore, the fatty coat is squeezed away, so to speak, leaving
the outer sheath and the central axis only to represent
the nerve fibre. It is this constricted bit of sheath running
transversely, and the central axis here seen, running, of course, longi-
tudinally, which stain in the silver preparation of the mouse’s nerve, and
thus produce the little black crosses here and there along the course ‘of a
medullated nerve fibre. ,
BIBLIOGRAPHY.
Quain’s Anatomy, Vol. 7, ninth edition (Longmans).
Grav’s Anatomy, ninth edition (Longmans).
Stirling's Histology (Smith, Elder and Uo.).
Sece.L - Llate/ [/
E]b dl adnat TW Watson. del ot lith
HUMAN CEREBELLUM.
c(h ete
Mitsor £ Son 93. Gt Charles Street Bun™
HUMAN CEREBELLUM.
Transverse Section x 150 diam.
(Stained with anilin blue-back.)
Etymology.—Commissure, Latin Committo, to unite. Cortical (cor-
tex, bark). Encephalon, év in, xepady the head. Falx, Latin, a scythe
or sickle. Fossa (from fodio to dig) a ditch or trench. Lamina a plate or
layer ofa flat form, which, however, may or may not be twisted upon
itself. Peduncles (from pes, afoot), Pia mater, a vascular membrane
investing the whole surface of the brain and spinal cord. Pinnate
(pinnatus feathered). Pons (Latin pons, pontis) a bridge.
THE ENcCEPHALON.
The great accumulation of nervous matter, generally termed the brain,
consists of four very distinct portions, namely :-—
The Cerebrum.
The Cerebellum.
The Pons Varolil.
The Medulla Oblongata.
Hoe Ge notes
By far the larger portion of the encephalon is the cerebrum, divided
into two hemi-spheres, which extend from the forehead to the back of
the head, also from one side of the head tothe other. As we shall give
a section and description in detail of the cerebrum in a future paper, we
here omit to mention more particulars regarding it.
The cerebellum is next with regard to size, and occupies a position
immediately beneath the hindmost third of the cerebrum. It is connected
by peduncles with the remaining three portions of the encephalon, the
peduncle above uniting it with the cerebrum: that below with the
medulla oblongata ; whilst the commissure, known as the pons Varolii,
unites the two symmetrical halves which go to make the cerebellum
itself. |
42 STUDIES IN MICROSCOPICAL SCIENCE.
The pons Varolii, or tuber annulare, is a thick band of nervous matter
arching forward, and stretching, as we have said, between the two halves
of the cerebellum. It is made up of transverse (commissural) fibres,
which are pierced by longitudinal fibres passing up from the spinal cord to-
the cerebrum.
The medulla oblongata appears to be the uppermost part of the spinal
cord, but lies within the cranium, hence it is said to be a part of the
encephalon. It is wedged between the pons Varolii and the cerebellum :
the former spans it and partly encloses it. It is irregularly cone shaped :
the thicker part of the cone being uppermost.
“The cerebellum or hinder brain consists of two lateral hemispheres
joined together by a median portion called the worm or vermiform pro-
cess. This isseen on the under surface in the fossa between the hemi-
spheres, asa well-marked projection named the inferior vermiform process,
but above forms only a slight elevation, the superior vermiform process.
In birds and in animals lower in the scale, this middle part of the cere-
bellum alone exists, and in animals it is the first part to be developed ;
moreover, in most mammals it forms a central lobe very distinct from the
lateral portions. The hemispheres are separated behind by a deep notch.
The upper vermiform process, though slightly elevated, is not marked
off from the hemispheres, so that the upper surface of the
organ, which is somewhat flattened in the middle and sloping downwards,
at each side, is uninterrupted. Below, the hemispheres are convex, and
are separated by a deep fossa named the vallicula, which is continuous
with the notch behind, and in it the inferior vermiform process lies con-
cealed in a great measure by the surrounding parts. Into this hollow
the medulla oblongata is received in front, and the falx cerebelli behind.
The greatest diameter of the organ is tranverse, and extends to about
three and a half or four inches. Its width from before backwards is
about two or two and a half inches ; and its greatest depth is about two
inches, but it thins out towards its lateral borders. The surface of the
cérebellum is everywhere marked by deep, closely set transverse fissures
which extend a considerable depth into its substance. One of these, the
great horizontal fissure, divides the cerebellum into an upper and lower
portion, corresponding in fact to the upper and lower surfaces, in each
of which there are several lobes.”
The internal arrangement of the grey and white nervous matter com-
posing the cerebellum is well seen in the accompanying slide. The
central part is composed of white nervous matter which sends out
divergent and gradually thinning layers into the interior of the laminae,.
larger and smaller, the grey nervous matter forming everywhere the outer
covering. In consequence of tlis arrangement of white and grey matter
sections of the cerebellum crossing the laminae present a foliated appear-
ance named arbor vitae. This appearance is seen in any vertical section,.
but is most conspicuous in a section which passes through the median
plane, where the relative quantity of the central (white) matter is small.
HUMAN CEREBELLUM. 43
The foliations are arranged somewhat pinnately, the sections of each
primary lamina having those of secondary laminae clustered round it, like
leaflets on a stalk. “The main br anches of the white (central) nervous
substance, or groups of them correspond with the lobules which, though
we have not mentioned it, receive names according to their shape, or
appearance, or position, or fancy of the anatomists who have described
them.
“The outer or grey nervous matter, also called cortical, is composed of
two distinct layers, having between them at their junction a layer of cells,
called the corpuscles of Purkinje. Outside the whole is the pia mater,
whose blood-vessels pierce the nervous substance. The two layers are
named respectively
The outer layer,
The inner layer.
The outer layer cousists of a delicate matrix, containing cells and fibres.
Most of the fibres have a direction at right angles to the surface; the
greater number of them are the processes of the large (Purkinje’s) cells.
The ced/s of this outer layer are granule-like bodies, some very small, and
belonging, probably, to the matrix, others somewhat larger, and probably
nervous, with processes extending from one or more sides. Some of the
corpuscles are connected with the processes of the large cells of Puikinje.
The inner part of the layer, contiguous to the cells of Purkinje, contains
nerve fibres running parallel to the surface.
The inner layer, that next the medullary centre, consists of granule-
like corpuscles, imbedded as close groups in a gelatinous matrix, which
contains also a plexus of fine nerve fibres. The corpuscles of Purkinje
dip into and are, therefore, almost surrounded by these granule-like
corpuscles.
The corpuscles of Purkinje lie, as we have said, between the outer and
inner layers of the grey cortex, They are mostly flask-shaped, with
their longer axis at right angles to the surface. Processes extend from
them into both the inner and outer layers ; the outer processes being by
far the larger and more conspicuous, branching and dividing as they
approach the surface. The inner process, after passing into the granular
layer, becomes the axis cylinder of a nerve fibre, therefore it is fine and
undivided.
The white (central) nervous centre of each lamina consists of nerve
fibres arranged in parallel or interlacing bundles, which pass from the
central or white matter of the hemispheres, etc., and appear to turn
obliquely into the cortical grey substance. These disappear in the
granule layer and are believed to be continuous with the axis-cylinder
processes of the corpuscles of Purkinje, but some anatomists are of opinion
that they arise in part by the union of the fine fibres of a plexus in the
outer layer.”
44 _ STUDIES IN MICROSCOPICAL SCIENCE.
Mops or PREPARATION.
The cerebellum of a human being, cat, dog, or rabbit may be taken and
cut into pieces half an inch square. These pieces are then to rest on
cotton wool on the bottom ofa jar filled with three parts of Muller’s fluid
and one of common alcohol freshly mixed, but allowed to cool before use.
Keep ina cool place during hardening. Renew the fluid in twenty-four hours,
then in seven days. The pieces should be left about twenty-one days in this
mixture altogether. They are then to be transferred to a large quantity
of a 2 per cent. solution of bichromate of ammonia for another fourteen
days to complete the hardening. Now wash away all the preserving
fluid by repeated changes of clean cold water and transfer to common
alcohol. |
Sections are to be made across the folia or leaflets either by freezing or
imbedding. The latter is preferable if very thin sections are required,
because if freezing be employed the leaflets are apt ‘to fall asunder, and
the pia mater also gets torn away. The sections are then to be stained
in an alcoholic solution of anilin blue-black make as follows :—
Take of
Anilin blue-black 1 decigram.
Distilled Water, 4 c.c.
Rectified Spirit, 100 ce.
Dissolve the dye in the water thoroughly, then add the spirit and filter.
This is to be kept in a well-stoppered bottle till required.
The sections are to be stained in the above, then cleared and mounted
in balsam in the ordinary way.
BIBLIOGRAPHY.
We have largely used Quain’s Anatomy, Vol. ii. in the above description, where a
full account will be found, accompanied by excellent wood-cuts. Klein’s elementary
histology (Cassell and Co.) also contains a clear, concise account.
Llatel2
SAE L
T W.Watson del clith. *
(after Klein.)
HUMAN CEREBRUM
Watson & Son talh 936 Charles 8¢ Bum”
HUMAN CEREBRUM.
a
Vertical Section of the Grey Matter of a Cerebral Convolution
Toy, LOO: diam,
Etymology. —Arachnoid (dpaéyvy, a spider’s web, esos, like) Arcuate
(arcus, a bow). Corpus callosum (corpus, a body and callus, hard).
Dura mater (mater, mother ; durus, hard).
GENERAL DESCRIPTION.
The largest part of the human encephalon is called the cerebrum, and
extends from the fore-head to the back of the head, also from one side of
the head to the other; the depth—roughly speaking—is from the top of
the head to a line drawn round the head through the eyes across the
temples and through half the ear-lobes, which would become a complete
band meeting high up on the neck. In other words the cerebrum is the
brain as seen from the outside, so to speak.
The cerebrum is composed of two cemetrical halves which nearly
touch. The two halves together form an ovoid mass flattened on its
under surface, having the front end the small and the larger end behind.
The two halves, though nearly touching throughout their course, are
separated by a very deep cleft called the longitudinal fissure. Hach
cerebral hemisphere, therefore, has three surfaces: a convex surface in
contact with the cranial vault, a flat surface which helps to form the
longitudinal fissure, and an irregular under surface which mostly lies on
the floor of the cranial vault.
The two large hemispherical masses we call the cerebrum are separated,
as we have said, by the longitudinal fissure, but in the middle this fissure
is not. complete. A large transverse mass of white brain-substance links
the two cerebral hemispheres together. This transverse mass of white
brain substance is called the corpus callosum or great commissure.
The surface of the hemispheres forms an arch corresponding to the
top of the head; the outer portion of the cerebrum or surface is not
smooth like an eg, but is composed of eminences called convolutions,
and depressions called sulci. Besides the ordinary swlcz there are deeper
46 STUDIES IN MICROSCOPICAL SCIENCE.
ones called furrows, which divide each half of the cerebral mass into six
lobes. These lobes from their position or function are called—
1.—Frontal.
2.—Parietal.
3.—Occipital.
4,—Temporal.
5.—Central.
6.—Olfactory.
At the present day it is of the first importance for a doctor to be able
to define pretty accurately the boundaries of these lobes. For our
present purpose, we may say roughly that the frontal lobe occupies the
front or fore-head ; the occipital lobe occupies the back of the head ; and
the parietal lobe the intermediate space, and so forth. The reason the
lobes are so important will be described presently.
‘ The interior of the cerebrum is studied by paring away successive
layers horizontally. The first cut displays the internal white matter of
each hemisphere, surrounded on all sides by the grey matter. This is
called centrum ovale minus. A second section on the same level as the
top of the corpus callosum discloses a still greater area of white matter
called centrum ovale majus. We now see that the white matter of the
hemispheres is connected by the corpus callosum itself white matter. A
third layer removed discloses the hollow space in each hemisphere called
the lateral ventricles. On the floor of each ventricle are several struc-
tures : the most noted being the two large masses of grey matter, the
greater part of each being imbedded in the white substance of the hemis-
phere in which it lies. These large ovoid masses are called the corpora
striata or ganglia of the cerebral hemispheres.
The brain and spinal cord being continuous structures are covered by
continuous membranes, three in number :—
1.—The dura mater.
2.—The arachnoid.
3.—The pia mater.
The dura mater is a very strong, dense, inelastic, fibrous tunic, which
adheres closely to the inner surface of the bones of the skull and forms
their internal periosteum, the adhesion being more intimate opposite the
sutures, but within the vertebral canal, z.e., as it surrounds the spinal
cord it forms a loose sheath. The dura mater within the skull is doubled
upon itself and thus is enabled to leave the bones and return to them at
the same place. Such a duplication is called a process. There are three
such processes or partitions, namely :—one running lengthwise from the
forehead to the back of the head in the middle line, which dips down and
separates the two hemispheres of the cerebrum: a second has a hori-
zontal direction, stretching across the back part of the skull between the
cerebrum and cerebellum: and a third which, like che first, is vertical,
and separates the two hemispheres of the cerebellum. By means of the
dura mater, therefore, the four large masses (2 cerebral, 2 cerebellar
hemispheres) which form the brain, practically, are partitioned off, and
enclosed with much firmness, but without pressure.
HUMAN OEREBRUM. “47
The arachnoid membrane invests the brain and cord closely, but does
not dip into the sule?. It is a delicate membrane, consisting of fine fib-
rous tissue bundles interlacing with each other. The intervals between
is spaces are filled up by delicate membranes, composed of expanded
cells,
The pia mater is a delicate highly vascular membrane, closely enveloping
the surface of the convolutions and dipping into the sulci of the cere-
brum. From its inner surface numerous minute blood vessels penetrate
the brain substance. The same also obtains in the case of the cerebellum.
Around the cord the pia mater is thicker, firmer, and paler (from being
less vascular) and more adherent to the nervous matter of the cord.
It will be seen then that the membranes of the brain and cord
have three distinct offices :—the dura mater mechanically supports ; the
arachnoid secretes serous fluid, which also acts as a packing agent; and
the pia mater supplies the means of life.
THE CorTICAL OR GREY MatTTER.
Our section and drawing give a representation of the grey or cortical
matter which caps the convolutions and dips into the sulci of the cere-
brum. It contains cells and fibres embedded in neuroglia, with numerous
blood vessels which pass vertically inwards.
The cells of this cortex are arranged in layers; the most external
layer is narrow and forms about the ~,th of the whole thickness of the
grey cortex. It is composed chiefly of neuroglia and contains a few small
cells with fine processes, probably not of nervous character. A few
medullated nerve-fibres occur in it forming a thin superficial white
stratum immediately underneath the pia mater. The next layer of
nearly the same thickness is characterised by containing a large
number of small nerve cells mostly pyramidal with branch-
ing processes. The third layer is of paler tint and much
greater thickness. It contains pyramidal branching cells, large and
small, arranged as above described, with the pointed extremities
towards the surface of the convolutions, and separated into groups by the
bundles of radiating nerve fibres. The inner portion of the layer, in
which the cells are larger and the separation into groups more distinct, is
sometimes described as a separate layer. The fourth layer is narrower,
aud contains many small irregularly shaped corpuscles, round or angular,
with fine processes placed irregularly and less distinctly separated into
groups. The fifth layer, of greater width than the last, and blending
more orless with it, is composed of fusiform and irregular cells. The
fusiform corpuscles have a definite arrangement, being placed for the
most part vertically at the summit of a convolution, but in the sulci,
parallel to the surface, where they correspond in direction to the arcuate
fibres passing from one convolution to another; they are said to be
connected with these fibres. Beneath the last layer is the medullary
centre with which it gradually blends.
48 STUDIES IN MICROSCOPiCAL SCIENCE.
The cells are of various forms and sizes, many of them have numerous
processes. Some of these branching cells are irregular in form and
position, but the majority are more regularly pyramidal in shape, with
the apex of the pyramid turned towards the surface of the convolution.
The average size of the larger pyramidal cells is the jginch in diaméter
at the base, and each has a rounded nucleus having an average diameter
of a inch. They generally contain a little yellowish pigment. The
cells often appear to lie in distinct cavities in the grey matter, but it is
uncertain if these are natural or produced by _ shrinking
after death. The process from the apex of each cell may be
traced for some distance towards the surface of the convolution,
giving off one or two branches as it passes outwards. The undivided
axis-cylinder process probably arises from the centre of the base of the
cell. The processes of these cells, as well as the body of the cell itself,
possess a distinct longitudinal striation. ‘The smaller angular corpuscles
are also provided with branches which run in various directions and
probably unite into a fine network. Rounded cells, having no visible
processes, also occur.
The fibres radiate from the white centre of each convolution in all
directions into the grey cortex having a course for the most part perpen-
dicular to the surface. In passing through the grey substance they are
arranged in bundles about the ,,, inch in diameter, and thus separate
the nerve cells into elongated groups and give the section a columnar
appearance.
Mopr oF PREPARATION.
If possible, we ought to obtain a portion of human cerebrum, and
choose a frontal convolution.
It is to be prepared like the cerebellum, as described in the last histo-
logical number, and stained with aniline blue black, and mounted in
Benzole Balsam.
BIBLIOGRAPHY.
The second volume of Quain’s Anatomy—from which we have largely quoted—
contains a very concise description, explained also by the use of excellent wood-
cuts.
If the reader wishes to know how very important a matter it is to know the exact
locality of the various convolutions, he should procure Ferrier’s work on the -
Brain (Macmillan and Co.) Ferrier has found by applying the interrupted current
to certain given areas on the convolutions of the brains of dogs and monkeys, that
he can cause the movements of various sets of muscles to a certainty thus :—By ap-
plying the current to one area he causes the hind leg to advance as in walking ; to
another given area, the tail is wagged ; to another, the shoulder is elevated ; to an-
other, the lip is elevated, and the nostril dilated ; also numerous other combined
muscular movements, can be produced with precision and certainty. When spicule
of bone or matter press on these known areas, that area the surgeon determines by
the results produced ; he trephines, and is able thus to relieve it of the offending
substance, which would cause death if allowed to remain. This terrible knowledge
has been obtained by taking away the skull-cap of numerous dogs and monkeys, and
as it has been the means of saving numerous human lives, and will doubtless restore
to his family many a human bread-winner in the future.
APPENDIX.
SECTION I.
ANIMAL HISTOLOGY.
——
Pace 9.—1. 5 from foot ; for ‘* cartilage is tissue” read ‘‘ cartilage is a tissue.”
PAGE 11.—1]. 2 from foot ; for ‘‘the white corpuscles is not,” &c., read ‘‘ the white
corpuscle isnot,” &c,
PAGE 25.—1]. 11 from foot ; for ‘‘ their areolar character of is shown” read ‘‘ their
areolar character is shown.”
PAGE 29.—I. 14 from top ; for ‘‘ the proportion of carbon and hydrogen” read ‘‘ the
proportions of carbon and hydrogen.”
Pace 44,—1. 13 from foot ; for ‘‘ solution of aniline blue black make as follows ”
read ‘* made as follows.”
Pace 45.—l, 15 from top; for ‘‘cemetrical” read ‘‘ symmetrical.”
Page 48.—1l. 2 from foot; for ‘‘and as it has been the means” read ‘‘and it has
been the means.”
INDEX.
SECTION I.
ANIMAL HISTOLOGY.
A
Adenoid tissue, 4.
Adipose tissue, 29, 31,
Amoeba, 2, 7.
Arachnoid Ereb rane, 46,
Areolar tissne, 21, 23,
B
BipLiioGRAPHY —Adipose tissue, 32,
Areolar tissue, 34.
Blood, 12.
Bone, 36.
Brain, 44, 48.
Cartilage, 19.
Epithelium, 16.
Nerve, 40.
Tendon, 26.
Blood, 9. (Corpuscles), 10, 11.
Bone, Development of, 33.
Brain, 41,
Cc
Cartilage, 17, (Hyaline), 18
7 (Elastic), 18.
¥ Ossification in 35,
Cell, Morphology of the, 1.
99
of Brain, 48.
;, Wall (The), 5
Cerebellum (The), 41, 42.
Cerebrum (The), 45,
Ciliated Epithelium, 14.
Columnar _,, 14,
Connective Tissue, 3, 21.
Corpuscles of Purkinje, 43.
Cortical Matter of Brain, 47.
Cytode (The), 1
33
D
Development of Bone, 33.
Dura Mater (The), 46.
E
Elastic Cartilage, 18.
Eucephalon (The), 41
(Lobes of), 46
(Fibro), 18
Theory (The), 1. (Rutherford’s), 5
Epithelium, 13.
ciliated, 14.
r columnar, 14.
glandular, 14.
pavement, 13.
stratified, 15.
transitional, 15.
F
Fat, 29.
Fibrin, 10,
Fibro Cartilage, 18.
Fibrous Connective Tissue, 21.
G
Glandular Epithelium, 14.
Globegerina, 8,
Glycerine, 29,
Grey matter of Brain, 47.
H
Haemoglobin, 11
Histology, 1
Hyaline Cartilage, 18.
Hydra, 2
L
Liquor Sanguinis, 10.
Lobes of the Cerebrum, 46.
M
Margarine, 29.
Medulla Oblongata, 42.
Membrane (ossification of), 36.
METHODS OF PREPARATION.
Adipose Tissue, 31.
Areolar 24,
Blood, 12,
Bone, 36.
Brain, 44, 48.
Cartilage, 19.
Epithelium, 16. °
Nerve, 39,
Tendon, 26,
3)
Mucous Membrane, 3. Protoplasm, 5, 8.
Muscle, 26. Purkinje (Corpuscles of),. 43
Muscular Tissue, 4.
Ss
N Serum, 10.
Nerve, 37. Stearine, 29.
Nerve cells 38 (fibres), 38. Stratified epithelium, 15,
Nervous system (The), 37. Stroma of blood, 11,
Newt, 6.
Nucleus, 2, 5. T
| Tendon, 25.
O Tissue adipose, 29, 31.
Oleine, 30. », areolar, 21, 23,
Ossification, 34. », White fibrous, 22,
9) yellow elastic, 22,
Pp Transitional epithelium, 15
Pavement Epithelium, 13. WwW
Pavardicee &. White fibrous Tissue, 22.
Polycystina, 8.
Pons Varolii, 42 | Y
Protomeeba, 2, 4. | Yellow elastic Tissue, 22.
| Sto Plate 7
E|D delad nat
TW. Watson del et lth.
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STUDIES IN MICROSCOPICAL SCIENCE,
SECTION II—BOTANICAL HISTOLOGY.
CHAPTER I.
Tur MorpeHouocy oF THE CELL.
Modern vegetable histology may be said to have had its origin in
SCHLEIDEN’S! enunciation, that the tissues of plants are built up of cells.
Literally, histology? is concerned with the general morphology of tissues ;
it is only since the introduction of the microscope, as an instrument of
power in anatomical research, that histology has ranked as a science
which deals exclusively with mdnute structure. The cellular nature of
vegetable tissues, especially of such as are likely to be examined by the
beginner, viz., those of the higher plants, is apparent at first sight when
viewed with even a very low power of the compound microscope, but it
must be borne in mind that when ScHuEemen framed his theory, he
laboured under technical methods of manipulation of a very primitive
character ; his discovery, therefore, marks an epoch in the history of
botanical science.
THe Crti TxHeory.—The foundation thus laid by ScHLEMmEN
in one department of biology, was speedily extended to in-
clude the more obscure nature of animal tissues, and ScHwWANN
immortalised his name at this early period by the statement
that, amongst animals, ‘‘ there 7s one universal principle for their develop-
ment, and that principle is the formation of cells,”® and this dictum is the
\MWiiller’s Archiv, 1838.
2Gr, loTOS, web, tissue; and Adyos, discourse. Also written Histiology, from
Gr. ioTiov, tissue.
3Mikroskopische Untersuchungen, 1838; Syd. Soc. Transl., London, 1847,
p. 165. :
2 STUDIES IN MICROSCOPICAIL SCIENCE
more remarkable from the fact that it was arrived at when the known
methods of investigation at the command of the histologist, were such as
to involve the utmost difficulty in research, and when the optical means
at his disposal were often quite unreliable. Even at the present nee
when microscopes and the methods of research have reached so high :
standard, that it may with justice be doubted whether they can be nae
improved, it is sometimes most difficult to imagine that certain tissues
are built up of elementary units, which preserve an individuality more
or less independent of each other. That such is in reality the case does
not now admit of any dispute ; all tissues that have hitherto been exa-
mined microscopically prove the universality of ScHwann’s doctrine.
But, whilst investigating the morphology of tissues, ScHwaNnw at-
tempted to account for their origin; and the imperfect means at his
command led him erroneously to believe that cells may arise de
novo by a_ sort of precipitation in a structureless pre-
existing substance which he called a cytoblastemu.! Ropert Brown,’
in 1833, drew attention to the nucleus, which had been figured as early
as in 1802, by F. Baumr,’? and Scuwann* applied the term nzcleolus, to
the smaller denser body within the nucleus which had already been
observed by ScHLEIDEN, but here again he fell into the error, that the
formation of the cell commences within the cytoblastema by the sepa-
ration and coalescence of particles which form the nucleus ; around this
centre an analogous precipitation produces the cell-wall, and between
these two, the so-called cel/-fluid accumulated. Barry,° and subsequently
Goopsir,° protested against this theory of cell formation, and established,
that all cells arise through regular descent from pre-existing cells.
The second great advance in histology was the discovery, by H. von
Mont, of protoplasm’ in the cells of plants, and here, as in the former
instance, its animal analogue was shortly afterwards identified by Coun,
Remak, and others. But now a complication ensued, which somewhat
retarded the progress of histological science ; ScHwaNn defined a cell as
essentially—a nucleus and a cell-wall ; to the cell-wall he attributed the
power to elaborate and modify the cell-contents, and this view of the
case was all but universally accepted, when Lrypia® pointed out the error
by showing that certain cells, e.g., pus, mucus, etc., do not possess cell-
walls, and that the cell-substance, or protoplasm, is the essential portion,
1Gr. KUTOS, cell ; Bracrnpa, bud, sprout.
2 Wiscellancous Botanical Works, Vol. I, p. 512.
3In the cells of the stigma of Bletia Tankervillie ; also figured in 1830 by MEYEN
in his Phytotomie.
4Schwann and Sch'eiden’s Researches, p. 38.
>Phil. Trans. Roy. Soc., Loudon, 1838—39.
6 Anatomical and Pathological Obser vations, Edinburgh.
‘Ueber die Saftbewegungen im Inneren der Zellen, Bot. Zeitg, 1846, p. ie:
SHandbuch der Histologie, 1856.
THE CELL THEORY. 3
from which the cell-wall is merely a secondary derivative, and is produced
either by condensation of, or secretion from, the protoplasm, or body of
the cell. Goodsir’s researches reverted to the importance of the nucleus,
and, from its frequent division preliminary to cell multiplication, he
averred that it must be the germinal centre of the cell. Such was the
condition of things, when, in spite of Lrypia’s demonstrations, VircHow!
insisted on the cell-wall as an indispensable moiety, and it was not until
1861 that Beate? and Max Scuuurzn* succeeded in abolishing the pri-
mary importance of the cell-wall once more. The cell was now considered
to be essentially a@ nucleated mass of protoplusm.
Vegetable histology again took the lead in the important announce-
ment by Brtcks,* that many cells, eg., the cells of Mung, are devoid of
nuclei; and once again it was speedily discovered that the nucleus is
not always present in the cells of animal tissues. Beate demonstrated
a minute non-nucleated colourless corpuscle in the blood, Scuunrze des-
eribed his now well-known Protumaba porrecta, and Harcxen laid the
foundation stone of the order Monera (the members of which consist of
formless masses of protoplasm which have been banded about from the
vegetable to the animal kingdom), in his then unique Protogenes
primordialis. And now, with the rapidly increasing variety of forms,
a complication arose, of a most serious character, which threatened
to throw histological nomenclature into chaos. Since Leypie, ReMak
and Scuuutrze had applied the term cell to a nucleated mass
of protoplasm, Harcken sought out a new name for his non-
nucleated form in its Hellenic equivalent — cytode, anil the term
came into general use. But this manufacture of terms would need to be!
carried to a much greater extent to be at all adequate, and new nmes
would have to be invented for such things as the cells of the periderm
of the higher plants, which have become thoroughly suberised, the corky
change having supervened to such an extent as to leave no trace of any-
thing but a thickened cell-wall, alike impervious to airand water ; or the
lignified cells and cell-fusions of woody-tissue, upon whose passive
mechanical properties the healthy continuance of the life of most of the
higher plants depends, would have to be described by other names, which
indicate that they consist merely of thickened cell-walls, from which
both cell-contents and nuclei have disappeared.
A way out of the difficulty has been pointed out by RurHErForp,’
who maintains that the classical term cell should be retained to indicate
any one of three things :—
1Cellular Pathology, translated by CHANCE, 1860, p. 12.
2The Sruc'wre of the Elementary Tissues, London, 1861.
3Miiller's Archiv, 1861, p. 18; Das Protoplasma, Leipzig, 1863.
4Die Elementar. Organismen. Sitz. d. hk. Akid , Wien.
5A Text-Book of Physiology, Kdinburgh, 1880, p. 30. Here the terms protoplast
and periplast are used as synonymous with cell-contents and cell-wall respectively.
They point to the relative positions of the parts of the cell. i
4 STUDIES IN MICROSCOPICAL SUIENCE.
=~ ee ee
lo, A simple protoplast, with or without a periplast.
20, A nucleated protoplast, with or without a periplast.
30, A periplast.
Examples of the first variety of the cell are to be found only amongst
the lower orders of plants, and most abundantly in that debateable group,
half plant and half animal, the Regnum Protisticum of Harcken. In
certain stages of some of the lower cryptogams, as amongst the Myaxomy-
cetes, (e.g. Didymium, Physarum, etc.,) plasmodia, or creeping masses of
protoplasm are formed which are not unlike some of the lower forms of
animal life ; their true plant nature has, however, been determined through
a study of their life- -history which is essentially analogous to that ‘of
other undoubted plants, the well-known Pandorinew.
But sooner or later most vegetable cells develop cell-walls of cellulose
and thus come under the second category ; instances are to be found in
almost all orders of plants ; amongst the Wungi the unicellular forms as
in the common yeast (Zorula or Saccharomyces Cerevisie), or the multi-
cellular mycelial varieties, (Agaricus, etc. ), possess only cell-walls and
cell-contents without nuclei ; the tissues of most of the higher plants
possess nucleated cells, and the cell-walls are usually held tovether by an
interstitial material, the significance of which will be fully discussed
hereafter. In some of the * Alge, this intercellular substance becomes
enormously developed and modified, so much so, that it seems to be
entirely distinct from the cellular elements, which appear to lie embedded
in it.
The epidermal tissues of plants, the outer protective coverings of
their organs, and the inner lignified elements which either remain
distinct and truly cellular, or become fused to form vessels or ducts,
are all examples of the third variety of cell, viz., a cell-wall from which
cell-contents have vanished. Although the lignified cells of woody-
tissue have lost their protoplasmic contents, they cannot be looked
upon as dead cells, because in the latter case a certain amount of
natural decay and disintegration would take place in the exposure to
which they are subjected; they are not dead although they are fune-
tionally passive. On the other hand, certain of the cells which lose
their contents and are eventually reduced to mere cell-walls, as in the
outermost layers of the bark of trees, are practically dead ; they are
to be compared to the desquamated horny epithelium of the skin of the
higher animals.
All these considerations taken together point to the diversified mor-
phology of the cell, but they also show, that its primary and essential
part is the protoplasm, or, as Huxuey! has aptly termed it, the
“oh leit hasis of life.”
hee Fe ors hema efe., London.
FORMS OF CELLS. 5
Toe Vartapiuity of Form 1x Cetis.—From what has already been
stated with regard to the nature of the cell, it naturally follows that in.
form cells present innumerable differences, and that these are dependent
upon the relative development of certain parts.
It has been pointed out that the protoplasm is the primary and essen-
tial part of the cell, for without it the growth of the cell ceases, and its
multiplication becomes impossible ; from it the cell-wall is produced, and
as the latter becomes larger and thicker, the protoplasm lessens relatively
in quantity, and, at the same time, contributes to the production of a
contained fluid, the cell-sap, until, finally, it is entirely absorbed, and
nothing save a dead cell-wall remains. This is the condition of things to
be observed in such a simple form as the common yeast plant (Succharo-
myces Cerenisice ). |
In order to understand the facts just stated, the development of the
yeast should be studied. The first or gemmiparous condition may be
observed thus :—
Procure some brewer's yeasti, and sew a small quantity in a vessel con-
taining the following modification of Pasrrur’s fluid2, and keep it in a
warm place.
Water (H, O).. : Bey ... 8576 parts
Cane Sugar (Cy. yy OR iti Jes ; oe 1500 nares
Ammonium tartrate (C+ H, (NH, ¢ cay oe O00 wim:
Potassium phosphate (KHz PO,) ... ee a's
Calcium phosphate (Ca, Pe Os) Late ag be IR
Magnesium sulphate (MgS Ot)... rity 2H §;
Oxygen (O)
Very soon the fluid will begin to froth up, and show that the active
life of the plants has commenced. ‘To make out the peculiarities of the
cells a high power of the microscope (about from 700-1200 diameters)
will be required. A small drop of the fluid should be placed on a glass
slip, covered with an extra thin cover glass, and examined. The cells
will probably be found in every stage of development. Some are
isolated, whilst others are connected in groups. Amongst the isolated
forms every variety may be discovered by the use of reagents, but it is
not always easy to find a group which shows every stage in the develop-
ment by budding of the yeast ; for this purpose it may be necessary to
keep the plants under continued observation for several days in a moist
chamber.
1This is commonly known as barm, (A.S. beorma ; Ger. .barme), and may be pro-
cured from any brewery, or from most public houses.
2PASTEUR himself used yeast ash, but the fluid given above is, easier to prepare,
contains all the constituents of the ash, with the addition of the ammonium tartrate
and sugar, and serves quite well for all ordinary purposes. (See PASTEUR, Comptes
Rendus, Paris, T. xlvii, p. 1011).
6 STUDIES IN MICROSCOPICAL SCIENCE.
Magenta solution! is perhaps one of the most’ useful in revealing struec-
ture here. A small drop of the dye should be placed on the glass slip at
the edge of the covering glass, and drawn through the field uf view by
means of a piece of blotting paper applied to the opposite edge of the
cover. It will be noticed that some of the cells will not stain or only be-
come faintly tinged when a strong solution of the dye is used ; these are
the old cells from which the protoplasmic contents have disappeared, and
are therefore merely cell-walls. Other cells become deeply stained, and
it may be observed that the smallest of them, especially those which
exist in the form of buds, imbibe the dye most readily of all.
These very young buds are apparently devoid of any cell-wall, but
gradually, as they grow older and larger, a very thin membranous enve-
lope may be discovered. The next stage shows the envelope plainly, and
at the same time the centre of the protoplasm becomes hollowed out,—a
vacuole 1s produced in which the cell-sap accumulates. That it is indeed a
vacuole, and not a nucleus, ordenser portion of the protoplasm, may easily
be proved. When the object i is living, and unstained, a slight variation
in the fine adjustment of the microscope causes it to become alternately
bright and dark, thus showing it to be a space of some sort in the
protoplasm. On the introduction of the magenta or other stain, this effect.
is only heightened ; whereas if it were a nucleus, as rarely happens to
be the case, it would become darkly stained, and remain so under
a slightly varying focus. Again, when such reagents as a strong solu-
tion of potassium hydrate or acetic acid are used, it disappears altovether ;
the reaction of these fluids being solvents of protoplasm, so that if it
were a denser portion of protoplasm, or a nucleus, it would at first resist
the action of the reagent and stand out in relief ; but, as it is only a space
in the protoplasm, it vanishes.
*
These confirmatory tests prove it indisputably to be a vacuole, and
that the space is filled with fluid is shown by its contour which is -
strikingly different from that of a bubble of air; the outline of the latter
is much more marked because of the greater differences in the refractive
indices of the two.
As the cell grows older the protoplasm becomes more and more vacuo-
lated, and the cell-wall increases in thickness ; either the vacuole becomes
larger, or several are produced. Finally, the protoplasm gradually lessens,
adheres to the sides of the cell-wall, and eventually disappears altogether.
The cell now consists of a mere envelope, its fluid contents are all ab-
sorbed, and it decays,—a sign of the absence of life.
1To make this solution, dissolve 1 decigr. of crystallised magenta (roseine) in
160 cubic centimetres of distilled water: add 1 cub, cent. of absolute alcohol.
Keep in a well-closed bottle. (Huxiry and Marrin’s Alementary Biology, 1879,
p. 269.) ;
FORMS OF CELLS,
Although the protoplasm can be observed clearly through the cell-wall,
it is otherwise demonstrable. If a small pad of blotting paper is placed
upon the top of the cavering glass of a specimen which has been stained,
and gently tapped with a pen- ‘holder or knife-handle, some of the crushed
cells will show the protoplasm clearly cxtruded from the cell-wall.
The action of iodine solution on the cells is of value to show that
they do not contain starch, otherwise they would show blue colourations.
Osmic acid is useful also to reveal particles of a fatty nature in the
protoplasm.
If now a small piece of dry German yeast is procured from a baker,
shaken up in a large test tube, and allowed to stand for about an hour,
the yeast cells will have separated sufficiently to enable them to be spread
upon thin slices of a freshly-cut potatoe ; this can be done with a camel’s
hair brush. The slices thus treated should be laid upon a plate of
plaster of Paris, this, in its turn, upon sheets of wetted blotting paper ;
or a blotting pad alone may be used, and the whole placed under a bell-
jar. The blotting-paper must be kept continually moistened with water.
At the end of the eighth or ninth day, a fine scraping may be examined
under a high power of the microscope, and will then show the process of
development by ascospores or endogonidia. This process may also be
observed by sewing ordinary barm in plain drinking water for a few
days.
The protoplasm of some of the cells will be found to sub-divide in-
ternally into four rounded parts. At first these ascospores are devoid of
any cell-wall; they are merely surrounded by the common envelope of
the parent cell. But as they develop, each particle secretes a cell-wall,
the original envelope bursts, and they are liberated to proliferate by
gemmation in the manner already described.
In both instances the buds or young cells began life as simple undiffer-
-entiated masses of protoplasm, to these envelopes were superadded, and
vacuoles developed. Lastly, the protoplasm, or seat of growth, vanished
vradually, until its total disappearance heralded death and dec cay. These
record some of the simplest cases in the development of the individual
cell, the external form of the cell varies but slightly during its increase in
volume.
Amongst the higher plants the growth in size of a cell from a simple
mass of protoplasm is usually accompanied by a variation in form whereby
an originally spherical or ovoid cell may ultimately become polyhedral,
elongated, prismatic, tabular, or even branched. These parts of the cell
(its ‘protoplasm and wall) may become so modified that they subserve
the special requirements of the various parts of the economy of the
plant.
In the reproduction of the common bladder-wrack (Fucus vesiculo-
sus) an excellent example is afforded of a simple mass of protoplasm
8 STUDIES IN. MICROSCOPICAL SCIENCE.
becoming clothed with a cell-wall, developing places for cell-sap and
eventually growing into a large complicated system of cells, some of
which perform special functions, but are nevertheless simple enough to
be compared with the primitive yeast plant on the one hand, and com-
plex enough to foreshadow the various organs of the highest plants on
the other.
Certain branches of these large sea-weeds possess peculiar enlargements,
studded all over with small spores, each of which opens into its respec-
tive conceptacle as these are termed. If thin slices of these conceptacles are
examined in salt water, or normal saline solution, those obtained from
the female conceptacles will be seen to contain certain large cells termed
oogonia. EKach oogonium consists of a cell-wall filled with a finely
granular protoplasm, which in its young condition seems to be quite
structureless, but ere long the contained protoplasm breaks into eight
nearly equal parts, known now as oospheres. The eight oospheres entirely
fill the cavity of the oogonium, and as they. are closely pressed against
each other, their external shapes are polygonal. The outer wall of the
oogonium now splits, and the eight oospheres are expelled, surrounded by
a very thin membrane, which once formed the inner coat of the
oogonium ; the membrane becomes distended by the absorp-
tion of water, and each of the oospheres now assumes a_ spherical
form. They thus collect in numbers at the mouths of their
conceptacles, while the fertile branches are lying outside of
the water when the tide has receded. On the rise of the tide, the thin
membrane bursts and liberates the spherical oospheres which are still
devoid of any cell-wall. At the same time other small bodies termed
antherozoids, are set free from the male conceptacles, and come into
contact with these naked oospheres. Profound changes now go on which
result first of all in the formation of a transparent cell-wall, and the cell
fixes itself to some external body, and begins at once to germinate. This
it does not do after the manner of the yeast plant, but the whole of its
cells remain organically united. The fixed portion produces a root-like
organ of attachment, whilst the free end develops leaf-like branches, on
which conceptacles are afterwards produced.
The cell-walls in these plants undergo a pecuhar change which is
common to most of the Aly, and which is worthy of attention here. If
a thin section of the thallus of the plant, preferably taken from its
thickened stem-like portion, is examined under a power of about 150
diameters, it is seen to consist of a number of cells which vary in form
in different parts of the structure, but which agree in producing cell-walls
of a two-fold nature. Each cell is surrounded by a wall which evidentiy
belongs to itself, but the interspaces between the cells are filled with a
material which differs from the ordinary cell-walls in that it is distinetly
mucilaginous. There is reason to believe that it is produced by a separa-
tion and subsequent coalescence of particles derived originally from the
primary cell-walls. . a
VARIABILITY IN FORM OF CELL: i)
In some of the simpler forms of Alge this jelly-like substance is often
used for social purposes. For example, many unicellular individuals,
like Gleocystis and Pulmella, are able to live together in colonies, owing
to the formation of stratified mucilaginous outer boundaries to their cell-
walls. In many cases comparatively large ‘‘ families” are formed, as in
Botrydina, while in others the co-operative result may be the formation
of a tube, or tubes, as in Hormospora, or a pear-shaped colony, as in
Apicystis.
But the cell-wall in unicellular Aigee may suffer a perhaps still more
marked and decided modification. The silicification of the cellulose
membrane, weakly developed in some desmids, is carried to the highest
possible perfection in the Diatomacete. These organisms varying infinitely
in form, and, from actual invisibility to our eyes, to an appreciable size;
are provided, as is well known, with flinty coats of mail, most wonderfully
marked with faultless geometricaldesigus, The cases or fristules, as they
are technically called, are two-valved, and as multiplication by division
is by far the most common mode of reproduction in this group, and also
as when the mature cell divides, an old half-frustule is retained by each
daughter-cell, while a new silicious half-case is built on the free face of
each separating rejuvenised mass, it of course follows that the two valves
are of different ages. Hach valve is made up of a back and an inturned
hoop-like rim or ‘girdle. The girdle of the old valve—often likened to
the lid of a pill- box—slips over the girdle of the younger, the line of
junction being descriptively known as the suture.
One of the disciform valves of the frustule of Arachnoidiscus
Ehrenbergii | Plate 3] is selected to illustrate this differentiation of cell
wall brought about in these, in other respects, simple organisms. The
genus Arachnoidiscus is distributed in the seas of both hemispheres, and,
according to Smith, Ehrenbergii is the only species belonging to Britain.
The gathering from which the accompanying preparation was selected
was taken in Monterey Bay, where the forms were found growing upon
sea-weed,
The valve, although so extremely thin, is nevertheless made up of
two distinct layers, as may be easily seen by using a good +} inch ob-
jective and focusing for the two levels. The outer layer is said to be of
a remarkably tough, more or less flexible, acid-resisting, horn-like nature,
while it is the inner coat alone that is impregnated with the silica,
The two layers can, by prolonged boiling in nitric acid, be actually
separated. I¢ will be noticed that the inner layer is marked with lnes
of puncta, arranged both radially and concentrically, and that there is
a central plain spot, the “pseudo-nodule” of descriptive writers.
Around this pseudo-nodule may be seen a well-defined double row
of “puncta,” the individual markings of the inner circle being linear,
while those of the outer are round. Respecting ‘the outer layer of the
valve, it is marked with radiating bars of equal lencth, springing froni
the circumference, and approaching, but not quite meeting, in the eentre,
their concentrically arranged terminations forming a boundary to the
double row of markings surrounding the pseudo-nodule noticed above ;
while shorter and less conspicuous lines of unequal length alternate with
10 STUDIES IN MICROSCOPICAL SCIENCE.
these more fully developed rays. To the somewhat striking resemblance
in appearance of these markings to aspider’s web the generic name of
this Diatom is due.
In the higher types of vegetable life we meet with a greater diver-
sity of form in cells. Here various systems of tissues are developed
to subserve the physiological demands of the more highly speci-
alised individual. A section through part of the body of
any vascular plant will serve as an illustration. A young shoot of
Scotch fir (Pinus sylvestris), seen in cross section, has been selected
(Plate 2). It presents, roughly speaking, five regions—(1) pith, (2) wood,
(3) cambium, (4) cortex, (5) dermis. The cambium zone, immediately
surrounding the green-stained wood, is made up of thin-walled elongated
cells, growing closely together, each cell presenting a brick-shaped out-
line in transverse section. A magnification of 30 diameters is not
sufficient to clearly define them, hence the drawing fails to show this
region with satisfactory distinctness ; but the preparation itself, examined
under eithera + or 4 inch objective will most clearly display it, These
cells, during the life of the plant, are filled with protoplasm, and never
(so long as they are members of the zone) advance beyond this simple
torula-condition. Like Torula, they require, as food, constructive
materials of an organic nature, and when so fed, also like Torula, they
multiply themselves by a process of division. The daughter-cells so
formed may advance towards no higher type of cell, as may be seen in
the plates (lines in the section) of cellular tissue connecting the pith with
the cortex.1 But, on the other hand, these primitive cells may morpho-
logically progress to a very special stage, as is exemplified by the tissue
cells of the wood. Here, to give strength to the structure and for other
physiological reasons, the cell walls are thickened from within, while, at
the same time, to provide for the passage of liquids and gases in all direc-
tions, numerous spaces opposite to one another on contiguous walls are
left unaltered, and the weak separating double membrane may eventually
become absorbed, thus making a direct communication between
neighbouring cells. These specialised cells (or tracheides as they are
termed) may be well seen by making a thin longitudinal section of any
of the Conifer, and after very carefully heating the slice in nitric acid
and potassium chlorate for some time, if it is transferred to a slide and
the cover glass gently tapped before examining, the “ pits” will be very
clearly observable.
The cells pushed outwards by the active cambium zone also become
specialised in time, but as the changes in form and physical properties of
this or similar regions will be the subject of future study, they need not
even be broadly referred to now, as our present object is merely to
indicate, in a general manner, the possible variability of form in cells.
SECRETION-CELL.—Cells may become strikingly differentiated from
neighbouring cells by becoming specialised to secrete from the circulating
1These rays being very narrow, are not shown in the drawing, but may
be easily made out in tiie preparation under a 4-inch obj., as the cells have
taken up the carmine stain.
SECRETION CELLS—OELLS WITH SPECIAL CONTENTS. ll
sap materials which, in some cases at all events, may be looked upon as
excrementitious matter. In the region of the wood in the seetion of
Pinus, such cells may be discovered ; they have taken up the carmine
stain. With a good 4-inch objective four nucleated cells lying in the
same plane will be seen, and, owing to the withdrawal, or rounding off,
of the cell-walls in each cell at the point where the edges of the four cells
primarily met, a space is left which serves as a receptacle or passage for
the material secreted by the cells. The material secreted by the Scotch-
fir is a resin which may be of special use in cases of injury to the trunk
or its branches, acting at once as a balm and protection to the suddenly
exposed surface or wound. In the cortical region owing to the formation
of a wider tube through repeated division of the four primary cells, wider
passages occur ; these are in communication with the wide resin passages
of the leaves?.
Crus with Specian Contents.—Biennial or perennial plants, whose
assimilating organs suffer destruction in winter, lay by during the season
of activity, a store of assimilated food to be used in the following spring,
for the purpose of nursing the buds through the critical period of nutri-
tive dependence—that is, until the green leaves burst and_ spread
themselves out to the air and light. The bulk of the reserve material
is usually starch, but it may be some other substance, isomeric with
starch, while always there will be mixed with it a small quantity of food
of a protinaceous nature. This constructive material is stored away in
cells, which must, of course, be thin-walled ; while at the period of the
in-filling, at all events, they must also contain working protoplasm.
To show these starch-containing cells, a section of the thick scale-leaf
from the bulb of Crown Imperial (fritillaria Imperialis) has been
selected. The preparation is stained with logwood. Those cells that
have not been cut into by the section knife, display a well-filled ca ity of
variously-sized granules ; while in some cells the old nucleus of the proto-
plasmic contents is still persistent. If thin sections are made from the fresh
bulb, cells may be discovered in all stages from those containing nucleated
protoplasm, with vacuoles, to the completely filled starch-bearing cells, as
shown in the preparation. It will be found that those cells lying
near the surfaces of the succulent scale-leaf will contain few or no starch
grains, but will exhibit in a marked manner the ordinary contents of
living cells, If the slice is treated with weak potash-water, the proto-
plasm may be seen dissolving away, leaving the large nucleus a very
conspicuous object in the cell. It would be well to study the starch
grains in a fresh specimen, either in section or isolated, by a process of
maceration. Inform they somewhat resembie one of the valves of the
shell of a fresh-water mussel. At the narrower end lies the hilum, and,
starting from here, concentric layers, alternately dark and light, may be
easily observed by a proper adjustment of the light. The potash solution
used above to display the nucleus, will cause these grains to swell so
enormously, and at the same time render them so transparent, that
they will become almost, if not quite, invisible.
1Vol. I. page 286—preparation 46.
12 STUDIES IN MICROSCOPICAL SCIENCS.
In the preparation, other structures can be seen, namely, sections of
the feebly-developed fibro-vascular cords that run up the succulent
leaves, from the -flatly-stunted stem at base of bulb, but as these have
no present interest, they need not be described here.
MstHops oF Preparation, &e.
The gathering from Monterey Bay, California, from which the valves
of ‘* Arachnoidiscus Ehrenberg,” for the accompanying preparation were
selected, is extraordinarily ‘rich, in respect of the variety of forms it
contains, yielding Arachnoidiscus’ Ehrenbergii (in profusion), Arach-
noidiscus ornatus, Aulacodiscus oreganus, Eupleuria pulchella (in
abundance), Isthmia nervosa, Hyalodiseus ste] liger, Hyalodiscus subtilis,
Triceratium arcticum (vars. a and b), and many small N avicule, Amphitetras,
&c.,&c. The Diatoms being in an exceptionally clean and perfecteondition,
growing parasitically upon an alga, the prolonged boiling in nitric aeid, fol-
lowed by sulphuric acid, which is ordinarily necessary, and from the effects
of which the valves frequently hecome seriously abraded, was avoided and
a perfectly clean and pure Diatomaceous residuum, easily freed alike from
heavy sand and light floating particles, obtained by means of the follow-
ing simple treatment. The ‘alga having been placed in a large basin, in
order to provide space for effervescen ice, Many organisms containing lime
being present, was left to soak for twenty- four hours in 5 parts water "and 1
part hydrochloric acid—2 parts more of the acid were then added, andafter
the subsidence of the renewed effervescence, the mixture was thoroughly
stirred for some time with a glass rod. The gathering was then carefully
strained through very fine muslin, water being poured upon it with con-
siderable force. The diatoms and finer sand, only, could pass through
the muslin, which retained the coarse sand and all the flocculent matter,
which it is so difficult to remove when the alga has been boiled together
with the diatoms. The strained matter was then boiled in pure nitric
acid for twenty minutes, some crystals of chlorate of potash being added
during ebullition. The acid was entirely removed by repeated
washings, and the gathering gently boiled for one hour (in a large
test tube) in a very weak solution of bicarbonate of soda, and,
lastly, repeatedly washed in distilled water. The diatoms, thus
perfectly cleaned, were spread upon slips and dried, the
finer forms being selected and transferred to covers, and mounted
in balsam. Most interesting “strewed” slides may be made from such
gatherings by allowing a drop of the cleaned material to fall (from @
heighth in order to spread it evenly) on to a covering glass from a glass
tube of small diameter, and mounting the forms so spread in balsam
or “dry.” The alga itself, also, if perfectly freed from salt by prolonged
caged in water, repeatedly changed, will yield beautiful slides either
“dry” or mounted in balsam. In. the litter ease the alea must be
placed in spirit after being removed from the water, and. afterwards in
turpentine, where it must remain for some days, in order that the air
may be expelled from the frustules and replaced by the turpentine,
before applying the balsam.
E|p 242 adnae TW.Watson del et lath
MICRASTERIAS DENTICULATA
X 200
Watson & Son teh 93,6¢ Charles St Burmng™
THE CELL AS AN INDIVIDUAL. 13
CHAPTER Il.
THE CELL AS AN INDIVIDUAL.
In Torula, as we have already seen, a single histologically simple cell
may perform all those physiological functions that are necessary for the
maintenance of life; and that under certain favourable external con-
ditions (presence of warmth, moisture, suitable food, and oxygenated
air) the cell will also grow, and in time increase itself by a process of
budding,
It was shown that the natural food out of which the protoplasm of
the light-shunning yeast plant was ab'e to construct new protoplasmic
material was sweet juices, the nutrient constituents of which had been
elaborated throuzh the vital actions of other plants, and that, therefore,
being itself unable to manufacture such ternary organic compounds as
sugar or starch, it is hence wholly dependent upon the energy of pre-
existing life for the greater bulk of its foo.l supplies.
In unicellular plants, having the power of producing chlorophyll, we
have individuals differing, physiolovieally, very widely inde d from the
torula type. These green cells have the power of producing, through
agencies at work within their own cell walls, the ternary compounds, so
essentiil for the construction of protoplasm, and the raw materials out
of which such compounds are manufactured are water (H2O) and
carbonic acid gas (COg). Provided, then, with such simple substances
in an available condition, and enjoying a suitable warmth together with
a proper amount of licht, such cells are able to .‘‘assimilate” within
their chlorophyll bodies either starch or some other material chemically
allied to that organic compound. Cells such as these, therefore, may
be looked upon as Nature’s laboratories, wherein inorganic molecules are
transformed into organic through the comLined actions of many converg-
ing energies focussed within the chlorophyll-bearing corpuscles ; while,
also, such green cells may be looked upon as pione rs of life, elaborating
not only necessary material for the use of their own protoplasm, but
making life—funyal and parasitical existence generally as well as animal
—really possible.
The organism selected to represent the individual life of a green cell is
the desmid Micrasterias denticulata. It is a not. uncommon plant, and
may be often found in boggy pools, or in the shallow water ditches of a
marsh. The specimens figured and distribute herewith were gathered
14 STUDIES IN MICROSCOPICAL SCIENCE.
last month (October) from a narrow, sluggish water ditch, in a boggy
slope on Wimbledon Common, Surrey. “The bottom of the ditch was
filled to a considerable depth with peaty matter, and, in certain places,
the thin sheet of water was fairly covered with this Micrasterias, some as
isolated individuals, others associating themselves in small colonies, or in
broad, deep masses, formed almost entirely of these cohering org inisms.
In the latter case the lower surface of the vreen mass was generally
attached to, or even mixed with, the soft brownish peaty matter at the
bottom of the ditch, making anything like a clean “dip” a matter of
some difficulty. This species of Micrasterias is, as may be
seen, a flat, obtusely-oval, much denticulated organism, the
mature individual presenting an all but complete separation
into two similarly shaped sub-hemidiscoid cells, each half being
partially separated from its closely opposed fellow by two deep,
straight, and opposite clefts ; the cell cavities being united merely by a
median, hollow, narrow isthmus of cell wall substance left as a junction
collar between the two bilaterally symmetrical half cells. The cell is filled,
or almost so, with a densely granulated, intensely green protoplasm, often
containing in addition, numerous, scattered, variously sized, oily-looking
globules. Each half cell is deeply indented into five primary ‘lobes, having
the free, lateral faces in each case plane and closely applied. Each lobe
(excepting the polar or terminal one in each half) is similarly indented,
but not more than half so deeply as the last, while the secondary lobes so
formed are themselves still again indented each by a shallow, wide, or
wedge-shaped cleft forming the ternar y and ultimate truncated denticula-
tions of the little plant. The primary polar lobes are narrower, and only
once indented while the sub-lobes are shorter than the secondary, but
somewhat longer and broader than the ternary denticulations of the
primary lateral lobes.
The endochrome does not, seemingly, fill the whole cell, but a clear
margin, varying in breadth in different individuals, may be seen along
the entire denticulated circumference of the cell. Widening at the
polar regions, it here forms a comparatively large and distinctive “vacuole-
like feature e; while a similar clear space, usually more or less round, .
exists in the central region—the isthmus above referred to—and its
immediate surroundings.
Under a good }inch obj., and by focussing exactly above the
endochrome, and just below the cell-wall, in a living and vigorous
specimen, a number of small, but variously-sized, clear-looking globules
may be watched moving, usually with a more or less jerky motion to and
fro between the clear space in the centre and the clear polar
regions. The clear space at the poles usually contains a consider-
able number of these granules, and these are always in a very
active free-moving state, owing, apparently, to the increase of
space discovered here, after their obviously partially retarded move-
ments over the surface of the endochrome. At the equatorial
clear space the number of granules is never so large, neither are
their movements ever so active as at the ends. Many granules, after
journeying to this region, seemingly strike themselves against some part
THE CELL AS .AN INDIVIDUAL. 15
of the cell-wall and then glide backwards, retracing their pathway in the
direction of the pole ; while others may be seen to pass through the neck
opening, and to accompany those granules that are seen streaming for-
wards towards the opposite pole.
The individual cell, forming the complete Micrasterias plant is able, as
before stated, to perform all the physiological functions required to keep
up the vitality of the contained protoplasm. Through its thin cell wall
the organism is able to absorb the soluble food materials existing in the
soft drainage water of the ditch, within which it lives. Oxygen and
carbonic acid gases are found dissolved in such waters, the former gas is,
of course, used for the purposes of respiration, the induced oxidation
liberating a sufficiency’ of heat for the proper maintenance of that
energy that is manifested by this as by all living things. The latter
gas, as is well known, is, under the influence of light and other
forces made to contribute, at least, its carbon element as: a needful con-
stituent of that product of green cell activity—starch.. The nitrogen,
phosphorus, potash, and such like, exist, combined with other elements
in the form of earth salts, in solution 4 in the water, and can, hence be
readily absorbed by the growing organism, From such simple inorganic
compounds then, the protoplasm of the desmid plants can. elaborate
all the constructive materials nécessary for its own increase and after the
growing cell has attained its full size and maturity it begins to divide,
while divison takes place in the following manner.
The protoplasm in the neck uniting the half-cells becomes specially
avtive, it increases in size and somewhat distends the cell walls, while
a double, median, new cell wall is soon formed within the canal,
shutting off therefore all direct communication between the two
half-cells. The protoplasm. still continuing active on each side
of the partition the two processes increase in size and, rounding them-
selves olf at their ends, soon become organically separated, a Ithough still
cohering by the viscid material, which is in this, as in other aloe
before noticed, derived from the substance of the cell-wall. A mutual
parting has thus taken place between the two mature half-cells of the
complete individual, and the small convex process now protruding from
the level face of each old half is the rudiment of a new half-cell that
will immediately grow, and, developing after the form and character of
the species, restore in time the bilateral symmetry of the cell.
During the season of greatest vegetative activity 1t seems that the
young “bud” grows most rap idly, and that the margins only assume
the characteristic denticulations by degrees, the final indentations
making their appearance when the young half-cell has attained:a size
almost equalling the older half—that is, as the young outgrowth
increases in size, its margin, owing to an unequal surface growth ‘of the
bounding cell-wall, first becomes shortly three-lobed; then, further increase
taking place, the. five primary lobes make their appearance, the twin
daughter half-cells. still continuing however to’ remain coherent by the
apex of their midlobes as is represented in the accompanying plate. The
secondary lobes will next be formed as the half-cell continues to increase
in size, while the ternary denticulations will be the last to make their
16 STUDIES IN MICROSCOPICAL SCIENCE.
appearance. In seasons of less vegetative activity these denticulations
may make their appearance, however, before the offshoot has arrived at
even half the size it will eventually attain, andl most of the multiplying
individuals observed in the present gathering were following this latter
mode of new half-cell increase.
All the individuals referable to the class to which Micrasterias belongs
(the Desmip1m) are inhabitants of fresh water and are characterised
(among other points) by the separation of the chlorophyll-bearing
protoplasm into two portions within the same cell. In some,
division of cell simply takes place by construction or formation
of a cell-wall along the median plane of colourless protoplasm,
while each new cell so formel grows independently, and attains
in time the size and appearance of the original or mother cell. In
many cases the cell wall surface grows equally, as may be observed in
Closter‘um—a desmid found in our present gathering, and as no pains
were taken to exclude it, it will, in the majority of cases, appear in the
same “mount” along with its near relation the Micrasterias. In the
various species of Staurastrum, on the other hand, we have forms whose
cell wall surfaces grow unequally as in Micrasterias, producing some
of the most beautiful and varied forms of cells to be met with in the
whole vegetable kingdom. Outside the desmid’s own class we have of
course many unicellular green plants, some like Chlamydueoccus, whose
cell-wall surface, growing equally all round, produce a more or less globu-
lar cell, while others like some species of Polyedrium produce more or less
star-shaped cells through unequal growth of the surface of the
wall; while in yet other cases we have as in Corlio-
lum, an elongated, club-shaped cell, the endochrome being
confined to the upper and wider portions of the cavity, while the free
end of the lower elongated hyaline portion is actually attached to some
support, thus foreshadowing the development of roots as hold-fast organs
in the higher plants.
In some of the Desmiliez (Didymoprium and Spheerozosma, for
example) after division of cell has taken place, and even after the
daughter-cells have attained their full development, instead of these
newly-formed cells separating from one another, they remain, cohering in
the midst of a rather copious supply of gelatinous cell-wail material, the
rod-like colony so formed having an appearance strongly resembling a
multicellular individual. In the same water as Micrasterias, a few
similarly-formed colonies of a species of Scenedesmus were observed. These
alow are small, oval-shaped organisms, living hy association in rows,
the two end-cells being each seemingly provided with a pair of slender,
or spine-like horns.
In Pediastrum we have still another example of a similar mode of life.
Here the cells form a four-, eight-, sixteen-, or thirty-two-celled, flat,
disciform colony, the outer boundary cell-wall surfaces of the marginal
cells growing unequally result in the formation of two ineurved horns to
each cell; while in Gonium, Pandorina, and the well-known Valvox, we
have this association-ship of unicellular forms carried to the very highest
state of morphological development. LA ole
West, Newman&C°lith.
TYPES OF SIMPLE TISSUES.
EID del. ad-nac. West,Wewman & C? lith.
PROTHALLUS OF FERN.
A 280.
CHAPTER lil.
THE MORPHOLOGY OF TISSUES.
INTRODUCTORY,
If portion of the thin layer of dark green slime so commonly seen
covering the sides and bottom of muddy roadside gutters be carefully
gathered, and examined under a suitable power, it will be discovered, in
all probability, to consist entirely, or almost entirely, of exceedingly fine,
yet rigid, short, wavy threads ; each separate filament presenting a slender
row of disc-like cells, resulting from the formation of frequent transverse
partition walls of extreme tenuity. In presence of a sufficiency of
moisture the filaments display peculiar oscillatory movements, hence their
generic name Oscillatoria. Like many of the Desmidee these organisms
may occasionally surround themselves with a rather copious jelly, and
form, in suitable habitats, lumps, or balls of greenish slime.
Oscillatoria differs structurally from Didymoprium and other Desmids
that form rod or thread like colonies in this important respect ; in the
latter, as we have before seen, the cells, or structural elements of the
filaments, are separate individuals, and in no way organically united,
whereas in the former the cells are not only physically, but biologically
connected, and the stock of available nutriment contained in the cell-sap
of any cell is, as it were, the common property of all the cells in the
same filament, and may be used for purposes of growth by protoplasm
located in any part of the multi-cellular individual.
The passage of nutritive lquids, from cell to cell, in many-celled
plants, has hitherto been explained by a reference to the well-known
physical process of osmosis; but from the important results of recent
researches by GARDINER, 1t now seems highly probable that the working
protoplasm contained within every living cell throughout the entire
individual, even in the highest plants, may be looked upon, in reality, as
one mass, as every cell-contained moiety of living substance would
appear to be in direct union, one with another, by means of very
slender threads of protoplasm, which pass through _ holes
of a corresponding fineness, left in the walls of the tissue cells. From
the highly suggestive results of this research, it would, therefore, most
certainly seem that the dissemination of nutriment from one living cell
to another takes plave, not by the operation of a mere physical process
of diffusion through a thin membrane, but rather by a vital process of
uninterrupted transmission.
Other common types of similar, but larger, filamentous forms may be
studied in Mesocarpus, Spirogyra, or Zygnema ; alge of extensive dis-
tribution in quiet, fresh-water pools throughout the kingdom. Spirogyra
Quart. Journ. Micr. Sci., Oct., 1882 ; Roy. Soc. Proc., Nov. 11th, 1882; Quart.
Journ. Micr Sci., April, 1883; Roy. Soc. Proc., April 26th, 1883.
18 STUDIES IN MICROSCOPICAL SCIENCE.
with its characteristic spiral arrangement of chlorophyll bands is, of the
three, perhaps the best known; anil, as it is admirably adapted for
observation it may be briefly referred to here.
As seen during its early growth from the mud-buried spore in the spring
time, and ata time when the young Spirogyra consists of a row of
merely a few cells, there is a manifest functional distinction between the
two end cells; one (the basal) is evidently concerned in holding the
the germinating thread to the spore which is safely fixed in the mud ; :
while the other (the apical) is free and specially active, adding new cells
to the young individual by repeated bipartitions, and, therefore, function-
ally differentiated to carry on the vegetative growth of the organism. As
the plant grows this differentiatior is, however, overcome, as, living in
waters where there is no possible risk of suffering harmful transportation,
and hence deriving no benefit from being permanently fixed, the basa] end
soon loses its early special function ; while, at the same time, each cell—
presumedly along the entire length of the filament—becomes empowered
to exercise self-multiplication by transverse division of contents.
This binary sub-division of cell takes place rapidly and during the
night. The different stages may be clearly studied by suddenly arresting
the life of the active protoplasm, which may be easily effected by
immersing (sometime after midnight), a wisp of vigorous specimens in a
phial of absolute alcohol which will not only kill the plants, but
fix, without contraction, their protoplasmic cell contents, or the different
stages of new cell-wall formation may be well seen by causing
the protoplasmic contents to suddenly contract, by placing the specimens
in dilute alcohol, or solution of sugar. The growth of the new partition
wall takes place gradually, and is, seemingly, initiated by a centralization
of vitality, quickly resulting in the formation of a median peripheral
ring of rather dense protoplasm, in which arises the collar of cellulose
cell-wall material. This process of special growth continuing, the
cell is ultimately sub-divided, while each twin cell, starting an in-
dividual development, increases in length, and ultimately reaches the
approximate size of the original or mother cell.
In the genus Conferva, represented by the green “ Silk-weeds” of our
coasts, we have multicellular plants structurally resembling the Spirogyra
so far as the arrangement of the cells in a single row is concerned ;
but here—the plants living in constantly agitated waters,—the basal cell
exercises its function as a hold-fast organ, during the whole period of
growth, while in the majority of cases, perhaps, the apical cell alone is
concerned in the function of vegetative increase.
As types of structure somewhat in advance of conferva, any species
of the genus Cladophora may be very conveniently examined. Clado-
phora ruprestris is marine, its shrubby tufts of dark green filaments
being attached to rocks over the entire breadth of the coasted tide-
run; while Cladophora glomerata is a very common fresh-water species
erowing from stones or other objects in almost every clear stream or
rock-girt spring.
In this genus, the threads, instead of being simply a single file of
cells, have spread themselves laterally by the formation of branches.
The primary branches arise in each case from the principal row or axis,
MORPHOLOGY OF TISSUES. 19
by the concentration of individual cell activity beneath a certain
spot in the cell wall. Towards this spot the nutritive sap is
specially directed, and the protoplasm here being over-fed, as it
were, increases unequally in bulk to the rest of the contents, resulting at
length in the growth of an offshoot, which becomes in time shut oft
from the main cell by the gradual formation of a cell wall very much
after the manner described in Spirogyra. Although the cells in Clado-
phora are filled with nucleated protoplasm, yet it seems that—unlike
what takes place in the vast majority of cases in the higher plants—the
nuclei are in no way concerned in the process of cell division. The
newly-formed lateral cell so produced will however increase in size,
and may ultimately sub-divide, forming in time a multicellular branch of
limited growth.
In Penicillium glaucum the common greenish-grey mould that covers
damp bread, old boots, and moist organic substances generally, we have an
organism structurally resembling in most points the Cladophora type,
although differing from it physiologically very widely indeed. Living a
saprophytic life, it feeds like Torula upon already formed constructive
material, and hence its cell contents are devoid of chlorophyll ; while
the filaments creep along or pierce below, the surface of the supporting
mass, only throwing up free aérial branches for the production of spores.
The hyphe branch dichotomously, and, as the branches of neighbouring
individuals closely interlace a rather dense, somewhat papery mycelium
is the result.
In Mushrooms (Agaricus) Peziza and other similar fungi we have
examples of how such well-defined structures may be built up
out of a vast number of interlacing hyphx, weaving themselves together
after a definite plan, but still the ultimate product of a single spore.
For example, when the mushroom spore germinates it forms a branching
underground mycelium, which, in process of time, throws up—not
solitary unbranched threads as in Penicillium—but numbers of erect,
aérial freely branching, interlacing filaments for the production of its
spores, the mature sporocarp being made up of the well-known, definitely-
formed structures—the stipes, pileus, and so forth.
In the stipes of the agaric, the hypha—as may be seen in the longi-
tudinal section of that organ—run vertically and parallel with one
another and so produce an elongated stem, upon the top of which is borne
the structure (pileus) carrying the inferior, plate-like, closely-set,
radiating, spore-producing organs, the /amelle. A section of the pileus,
as given in the accompanying preparation, displays the hyphe running in
all directions and freely interlacing, forming the broad, thick, more or
less spongy, cap-like mycelium—but a tissue withal that is built up of
simple hyphe resembling that of Pendcilliwm.
The thallus of a Lichen is structurally composed of similar interlacing
fungal hyphae, growing, not in genetic connection, but parasitically
upon unicellular or multicellular algee, which form a green or ‘‘ gonidial ”
layer, completely surrounded by the insinuating threads of the domi-
neering fungus. Physiologically, these fungi possess an immense advan-
tage, as they have their hosts, or food producers, under complete control,
20 STUDIES IN MICROSCOPICAL SCIENCE.
and are hence able to live under conditions, and affect habitats, totally
unsuited to the wants of any of the other members of this food dependent
group.
In Cladophora (to return to that type), cell multiplication takes place
in apical cells. In the main filament or axis, growth may be described
as being practically unlimited, while the frequency of bipartition is often
very limited indee ‘d, in the apical cells of the lateral branches.
Chara and WNitella, slender-stemmed alga-looking gregarious plants,
with whorled leaves, found submerged in many fresh water pools and
streams, grow as Cladophora does, by terminal and lateral apical cells,
and they illustrate, in a marked manner, the apparent comparative com-
plexity of structure, arising from a difference in the subsequent indi-
vidual course of growth of the successive new cells, cut off from the
active apical one.
But before the leaf-bearing structure, which ‘ultimately carries iat re-
productive organs, arises, a “distinetly ale:
is produced. This is an unbranched oscillatoria-or conf Peay
with limited apical growth, which grows directly from the spore, and
from some special cell of which, somewhere behind the apical one, an
erect off-shoot cell arises, which ultimately develops into the ordinary
leafy-stemmed individual.
Every fresh celi arising from the bipartition of the apical follows one
of two lines of deve lopment ; it will either lengthen itself in the ordinary
or conferva-like fashion producing a cell often. of considerable length ;
or it will remain short, and, retaining the primitive function of self-
division, will proceed to break itself up into a ring of sub-cells by the
formation of numerous vertical septa. This plate of small cells is known
as a node, and as the new cells formed from the apical cell follow the one
mode or the other alternately, nodes in the stem are always separated by
the long one-celled internodes. The nodal cells then throw ont offshoots
which, like the branches of Cladophora not only in their origin but in
the limited growth of their apical cell produce the nodal whorl of leaves
so characteristic of the Characee.
In Funaria, or other leaf-bearing Moss, the spore so far resembles a
uni-cellular alga, as to consist of a single mass of walled protoplasm, con-
taining oil, grains of starch, and chlorophyll. When this spore germi-
nates, it forms ad: itk-green, branching, uni-cellular, eladophora-like
structure, known as the protonema, which may in its growth, cover a
comparatively large surface, while, at the same time, possessing the power
of assimilation, it may have a somewhat extended period of existenice,
Each filament of the protonema increases in length by bipartition of
an apical cell, the newly-formed transverse walls being always oblique,
an important character in the vegetative development of the moss plant.
From one or more of the cells a vigorous lateral filament may vertically
arise, the apical cell of which dividing very rapidly and with oblique septa,
throws back short cells, cut off in such a spiral manner, that they must
of necessity intercross in their growth, and hence a structure of many-cell
thickness may be form«d, resulting in the formation of a stem which, so -
far as it alone is conceined, may therefore be looked upon as a highly de
veloped or specialised filamentous alga.
MORPHOLOGY OF TISSUES. AM)
The forked Scale-Moss ( Metzgeria furcata) a gregarious plant very
common on stones, rocks, and trees, presents another and different type of
structure, being composed of a flat surface of chlorophyll-beariug cells,
forming a thin, membranous, and, as the name implies, forked thallus,
varying, in size, from a half to three-quarters of an inch in length. This
thallus is only one cell deep, excepting along lines or bands carried back-
wards from the forks—the midribs—where the cells are several in depth.
Along the anterior margin of the thallus, and lying within the depression
of each of the younger forks, is an active, apical cell, where all new growth,
by cell-multiplication, is initiated. Larlier, that is just after germination
from the spore, growth was carried on by means of a single, apical cell,
but, as the thallus increased in size, similar cells at different points, right
and left, eventually arose, and aided in the production of the bifurcating
structure, so characteristic of the mature individual.
When viewed from either the upper or lower surface, the apical cell has
the form of an isosceles triangle, the base of which is curved and directed
forward, and hence always free or exposed. New cells are produced first on
one side and then on the other by the formation of oblique walls, alternately
parallel with opposite sides of the flat, triangular mother-cell. The
daughter-cells so thrown off form. on each side, therefore, a plate com-
posed of a series of diverging cells, the inner, end walls of which form a
zig-zag median line carried back from the growing point. The cells so
produced still retain the power to divide, and they enter at once upon
a rather vigorous period of growth. Each daughter-cell is first of all
divided by the appearance of an obliquely transverse wall, forming a
posterior (smaller) and anterior (larger) cell, the subsequent growth of
which respectively is carried out along very different developmental
lines.
The posterior cells—all of which are lying, of course, on one side or the
other of the before mentioned zig-zag line—increase by the formation of
divisional walls, produced in two directions. The first formed cell wall
in each of these ceils, cuts the cell in a plane, parallel with the surface of
the thallus, thus producing two superimposed cells, and as all subsequent
bipartitions are made either parallel with or at right angles to the surface
of the thallus, a band of tissue—the midrib— of several cells in thickness
is the ultimate structural result.
The anterior cell divides only by vertical walls, and as the cells grow
rapidly, and also as cell multiplication is rather frequent, a flat, luxuriant
tissue of one cell deep is formed on each side, and these, spreading them-
selves to the right and to the left, around and beyond the growing apical
cell, produce in time the characteristic thalloid forks of our type.
In the common horse-tails or Hquisetum, the individual passes through
two distinct life periods or generations—one a simple, vegetative structure,
which grows from the spore, producing early, in point of time, the
essential organs of sexual reproduction, and the other a spore-bearing
i)
bo
STUDIES IN MICROSCOPICAL SCIENCE.
structure, formed of variousiy differentiated tissues, the result of a more
specialised, vegetative growth from the fertilised oosphere.
The unicellular spore is a walled mass of nucleated protoplasm, and
contains, like the spores of /unaria, distinct grains of chlorophyll.
When the spore escapes from the sporangium of the parent, and falls
upon damp earth, it almost immediately germinates. Owing to a one-
end growth or elongation, the spore first of all assumes a pear-shape form,
and then divides, forming two cells of unequal size. The smaller is the
narrower, and its contents are colourless and non-granular. It speedily
lengthens, forming a comparatively long root-hair. The larger does not
lengthen but divides, the division walls being formed parallel with the
axis of strongest growth forming two cells lying side by side.
These cells containing chorophyll, and hence possessing the power
of assimilation are self-supporting ; they enlarge, and division soon takes
place again, but this time in a direction at right angles to the first, and,
as growth continues, so the cells divide, forming in time a flat plate of
cellular tissue—the simple prothallus, or individual, representing the
sexual generation of the horse-tail. In this stage the structure of the
vegetative body of the equisetum advances no further than that found in
the simplest of the scale-mosses, and, it is not until the subsequent growth
and development of the generation that arises from the fertilised germ
cell contained within the archegonium produced upon the under surface
of the prothallus, that the different systems of tissues are formed
that are so characteristic of this latter stage in the life history of
the plant.
In this latter, morphologically higher structure, apical growth is carried
on through the activity of a single cell. This cell has the form of a
triangular pyramid, having its curved, three-sided base lying in front, and,
therefore, free or exposed. A new cell is cut off in regular, intermittent
succession by the formation of a wall parallel in turn with each
of the three sides of this apical mother cell, and as each succeeding
new cell after its appearance lies at a slightly higher level than -
its just previously formed fellow—owing to the interim growth of the
apical cell—the primary daughter cells traced backward from the growing
point, form one-third segments of a descending solid spiral. With the
subsequent mode of growth of these cells we are not at present concerned,
but the ultimate result of their further division, and clearly marked
differentiation may be learned by an examination of a transverse section
made through any part of the stem a little distance behind the growing
point!. F
The prothallus of a Fern has been selected in illustration of a tissue
formed merely of a plate of cells, and the genus Péeris, in an early stage
of growth, has been made the subject of the accompanying drawing.
1SrupDIES IN MicroscoprcaL Science, Vol. I. ; see article—The Field Horse-Tail,
page 127, and Preparation and Plate of T.S. of Stem.
MORPHOLOGY OF TISSUES. 23
—_
Taking the particular individual here represented}, there is, as may be
seen, an uniserial thread of three cells length, as the first-formed product
of the germination of the still persistent spore. The rudimentary pro-
thallus grew, so far, at all events, by the formation of transverse walls
alone, and, therefore, at this stage, it exactly resembled in its mode of
vegetative increase a filamentous alga, and the protonema condition in
the life history of a moss. Indeed, in one species of Hymenophyllum
(the filmy ferns) a cladophora-like protonema is produced from the spore,
upon which prothalli subsequently appear as offshoots, exactly as the
homologous, sexual generation of a moss plant is similarly produced as
lateral buds from the moss protonema.
As the development of the prothallus advanced a partition wall arose
in the terminal cell of the row, having a direction at right angles to that
of the previously formed transverse walls, producing the two
cells~ that are seen lying side by side immediately beyond
the first formed series of three cells. Growth continuing, and
cell-multiplication taking place by repeated transverse and longitudinal
bipartitions ; a broad surface of cells such as is here shown is the ultimate
structural result. Imbeddedin the protoplasm are well-formed grains of
chlorophyll, and by the icdine test the presence of already assimilated
starch may, in fresh specimens, be also easily discovered in the cells.
Long, unicellular, root hairs are produced from certain cells as the result
of an unequal growth of the walls. These are functionally concerned in
the in-taking of water and soluble earth salts, The rudiments of sexual
organs are also shown in the drawing.
As in Hquisetum, so we find in ferns that the complicated histological
structureg that eventually grows up from one of the fertilised oogonia of
the simple prothallus, is produced through the activity of a single apical
cell, the segments thrown back becoming gradually modified to subserve
the functional requirements of a highly-developed organism.
EXPLANATION OF PLATE YV.
I. Filaments of Oscillatoria.
II. Portion of filament of Spirogyra.
III. Cell of Spirogyra, in the act of division after contraction of the cell-contents
by the addition of the solution of sugar; the portion of the cell-wall,
already formed, being thus made visible (THOME).
IV. Portion of branching filament of Cladophora.
VY. Portion of filament of Cladophora, showing process of cell-division (CARPEN -
TER).
1As the accompanying preparations cannot possibly be all alike, a typical indi-
vidual—the one sketched—has been selected and described.
2STUDIES IN MicroscopicaL Science. Vol. I. See Art.—Bracken Fern, p. 75,
and Preparation and Plate of T.S. of Rachis.
24
STUDIES IN MICROSCOPICAL SCIENCE.
" Ponieltlinum. (a) Spore just commencing to germinate. 0) Same further. advan-
ced. * (c) Portion of mature hypha.
. Interlacing fungus hyphe.
. Portion of underground hyphee of Agaricus, with young sporocarps (SACHS).
. Portion of lichen thallus, showing gonidia surrounded by fungalhyphe. 4
. Chara, showing growth of pro-embryo from spore (SAcHs). a
. Growing point of Moss ( Funaria ), (SACHS),
. Spores of Moss germinating (SACHS).
. Protonema of Moss.’ (a) Main filament. (0) Branch’ of protonema. (c)
Young bud. (d) Rootlet (SAcHs).
. Growing point of Chara (SACHS).
Spores of Equisetum germinating. (a) Commencement of germination. .(b)
Later stage (SACHS).
Plate 7
Sec:
TW Watson del et ith-
L.S. THROUGH APEX OF ROOT OF MAIZE
(Sachs )
Watson & Son, lth 93 C¢ Charles 5¢ Burrriung™
PRIMARY TISSUE.
In the Vascular Cryptogams as represented by the genus Equisetum,
a single apical cell by its growth and continuous bipartition gives rise to
amass of primary tissue composed of a number of active daughter cells
that are the direct progenitors of all the variously modified, histological
elements of the different tissue systems of the mature individual. A
similar tissue, having the power of self-division and capable of sub-
sequent development, exists at the apex of the stem and root in plants of
a higher order—the Phanerogams. Except, however, in a few extremely
rare cases,’ the primary tissue does not arise in these flowering plants from
the activity of a single apical cell, but from several cells (not unfrequent-
ly four), all the cells of the group being of equal histological value. The
possibility indeed of the existence of a solitary apical cell is, it would
seem, entirely prevented by the characteristic mode of cell division that
takes place during the early embryological development of these plants.
The oosphere or germ mass in the Phanerogams is contained within
the embryo sac—an extraordinarily developed sub-epidermal cell of a
special structure, the ovule. After fertilisation is effected, the oosphere
clothes itself with a cell wall of cellulose, gets somewhat elongated, and
becomes attached, by one end, to the inner wall of the enclosing vesicle.
The impregnated oosphere then divides, by a cross-partition wall, into an
upper (attached) and lower (free) cell. The upper cell then next
divides by the formation of a transverse septum, and, growth continuing,
this simple mode of cell increase may be repeated several or many times,
producing, at length, either a short or long conferva-like thread known
as the suspensor. When the lower or embryo cell divides, it does so,
first of all, by the formation of a median longitudinal wall, hence the
two resulting daughter cells are of the same size, and lie, not end to end
(as in the suspensor), but side by side, and as they both retain the
power of self-multiplication and, also, as the direction of the
next division wall is at right angles to the last, a globular
mass of four cells is soon found at the end of the suspensor.
Each of these cells will again divide, and form an _ enlarged
sphere of eight cells and so on; but it is just somewhere about this
stage in the development of the embryo that the first differentiation of
tissue manifests itself. Owing to tangential segmentation, an outer layer
of cells is cut off—the dermatogen or rudimentary epidermis. At this
stage, therefore, we have a cluster of cells touched above by the end cell
of the suspensor, and bounded on all other sides by these recently
developed cells of the dermatogen. This end cell of the suspensor that
is in contact with the daughter cells of the embryo-cell, is endowed with
a potential of growth and development unpossessed by the other cells of
lEleocharis palustris, according to Schwendener, has an apical cell, while on the
authority of Dingler the seedlings of Picea excelsa havea single apical cell, although
this disappears in the older plants.
26 STUDIES IN MICROSCOPICAL SCIENCE.
the suspensor. This cell is known as the hypophysis, and is ultimately
destined to take a greater or less share in the formation of the embryo.
When, in due course, activity sets in, the first formed cell wall lies
transversely to the longer axis of the suspensor, and it is the
lower of the two cells thus formed that gives rise in
a great many cases. to the primary tissue of the embryonic
root. Just as in the case of the embryo cell so in this the lower cell of
the hypophysis, the first formed septum arises in a median longitudinal
direction forming two twin cells lying side by side; and this division by
longitudinal walls may continue until a number of cells are formed, after
which, by the formation of transverse or tangential walls, a layer of outer
cells arise, which are continuous with the similar but previously formed
dermatogen cells of the rest of the rudimentary plantlet.
REFERENCE TO PLATE 7.
Longitudinal section through the apex of the Root of Maize (after Sachs).
a. group of apical cells.
b. calyptrogen.
c. dermatogen.
d. periblem.
e. cortex.
f. epidermis.
g. cuticle.
h. t. k. plerome.
h. cells that will develop into xylem or wood.
i. row of cells that will produce a vessel.
k. pith.
i. younger layers of root-cap.
m. older layers of root-cap.
It is in this way, therefore, that the ‘developing embryo becomes
possessed of two apical growing regions that tend to lengthen the plant
in two opposite directions ; and where growth, instead of being carried
on by single apical cells, takes place in each case amid a group of cells
that arose as we have just seen as the result of longitudinal, instead of
transverse, septa, taking place in each of the two primary cells of the
future stem and root.
As cell multiplication goes on, and development advances, a further
differentiation of tissue soon takes place in the now slowly lengthening
organism. The majority of cells pushed back or left behind by the
active apical cells, enter upon a special course of individual development,
and consequently lose all power of self-multiplication ; some for example
are destined to become fibrous, others to become fused together in rows
NOTE.—In the plate, one half of the Section is drawn, as it appears, under
normal conditions ; in the other half, the Section has been subjected to the action of
potash which has dissolved out the protoplasm, and left the cell-walls clearly
defined,
PRIMARY TISSUE. 27
forming tubes, while the cells in another region may suffer little or very
little change in form, becoming simply inactive through loss of proto-
plasm,—and so on. |
A central mass of tissue may be early distinguished, as being the
primary tissue out of which the future pith and fibro-vascular systems
will arise. It is known as the plerome. Surrounding this, and bounded
externally by the dermatogen or rudimentary epidermis is the periblem,
or primary tissue of the cortex. As the radicular end of the embryonic
axis grows, at first, much more rapidly than the plumule or stem end,
the radicle, in most embryos is much more conspicuous than the plumule,
whose longitudinal growth is usually delayed by the production of lateral
outgrowths, or rudiments of future foliage leaves. The radicle is,
therefore, a more convenient subject than the plumule, for studying the
histology of the growing point, and itis the growing point of the root of
a germinating embryo of Maize, that has been selected to typically
illustrate the primary tissue of Phanerogams.
While the region of apical growth in the stem is protected by the
rudimentary leaves of the bud, the growing point of the root (which pro-
duces no lateral parts, at all homologous with leaves), is furnished with a
special protective development, the root-sheath or root-cap. This, in
the Maize, is derived (according to Janczewski), from a special region of
active or meristem cells lying in front of the growing point, and to which
he has given the name of calyptrogen. The new cells cut off by this
vigrous layer, are gradually pushed outwards, adding layer after layer
to the depth of the “cap,” until a structure of considerable thickness is
formed. As the cells become further and further removed from the
layer of primary mother cells they gradually lose their contained proto-
plasm, and eventually die; hence an inner part where the cells are filled
with protoplasm and closely arranged; and another region where the
cells are empty and rather loosely placed may be easily distinguished in
the section. The cells of this latter region are being continually rubbed
off by friction against the particles of earth in the soil, in which the roots
of the plant are growing.
Lying behind the group of apical cells and taking up a central posi-
tion in the section, we have the plerome. In this, longitudinal rows of
short but broad cells completely filled with granular protoplasm, and
each exhibiting a very large globular nucleus may be clearly seen, under
even a l-inch obj. power. Associated with these are narrower, but
longer, or at least as long, cells, also filled with granular, nucleated pro-
toplasm. Some of these will develop into fibres or wood cells; while
others will contribute to the formation of a pith.
The periblem lying around the tip of the plerome (on each side
of it in the section) is also made up of small cells completely
filed with granular nucleated protoplasm, but if this be traced
backwards into the cortex (which as_ has been already said,
is produced from it) the individual life history of each cell
may be very clearly traced. As the cells get older, they enlarge
28 : STUDIES IN MICROSCOPICAL SCIENCE.
and vacuoles or water cavities soon make their appearance in the midst of
the protoplasm. Further back, representing still older cells, the vacuoles
have become much bigger, and the nucleus may be generally seen lying
in the centre, or almost in the centre of the cell, with strings or bands
of protoplasm connecting it with the peripheral protoplasm or the proto-
plasm closely adhering to the inner side of the wall of the cell. In yet
older parts of this tissue the various vacuoles in each cell have coalesced
to form one large sap cavity, the nucleus being driven to one side and
forced to embed itself in the peripheral protoplasm.
The dermatogen, it seems, is derived from the same meristematic layer
as the periblem: continued backwards, it forms the epidermis, the outer
or exposed walls of which become somewhat thickened and eventually
coalesce to form a continuous, specially protective layer—the cuticle. _
In different plants, or groups of plants, there are widely varying
differences in the histological structure of the apical meristem region of
the root. The most recent contribution to the comparative structure of
growing points is comprised in the comprehensive researches of
JANCZEWSKI. These have been summarised by Dr. Vines, from whose
abstract we extract the following notes :—
Type 1. The meristem consists of four distinct layers, Plerome,
Periblem, Dermatogen, and Calyptrogen ; Example,
Hydrocharis Morsus Rane.
Type 2. A distinct Plerome and Calyptrogen ; the Periblem and
Dermatogen have common initial-cells; Hxamples, Many
Monocotyledons (Maize, &c.)
Type 3. A distinct Plerome ; the Calyptrogen, Periblem, and Der-
matogen have common initial cells; Hxamples, Many —
Monocotyledons (Lilies, &c.) :
Type 4.
W Watson del e& Lip.
E[D del ad rat
T.S. OF AERIAL ROOT OF DENDROBIUM.
130
™
Burm
Lh 93.0¢ Charles 5°
Watson & Son
EPIDERMAL TISSUE.
Tn all the higher or vascular plants, we meet with a more or less well:
developed, and, genetically distinct outer or boundary tissue-system—the
Epidermis, which, in its earlier stages at all events, consists of a single
layer of flattish, closely-fitting cells, usually sharply differentiated from
the underlying tissues. Certain cells of the epidermis may develop into
guard cells of stomatze, the portals of an intercellular aérial system; while
others may produce hairs of various forms and functions.
Among the lower forms of vegetable life, as included in the sub
- kingdom THatiopuyta, there is no absolutely strict morphological dis-
tinction between the general mass of body tissue and its sometimes
apparently distinct, investing, protective layer. Even in such individuals
as Laminarza among the Sea-weeds, and Puff-balls among the Fungi, the
dense and clearly seen boundary layer of the one, and the easily separable
boundary layer of the other, are formed of cells genetically equivalent to
those of the rest of the thallus, but physically and functionally modified
to subserve the special requirements of their respective growths.
As we ascend, however, into the next sub-kingdom—the Muscinza,
we discover a number of forms, each presenting a truly distinct epider:
mis. In Metzgeria, referred to on page 21, we have a simple member of
this small, but highly interesting group: but the thallus of Metzgeria
being—with the exception of the ‘ mid-ribs”—merely one cell deep, a
boundary layer of any kind is, of course, entirely absent. In Anthoceros
(Horn-liverwort), although the lobed thallus is formed of several layers
of cells, yet the upper or exposed layer presents no differentiation what-
ever from the layers upon which it rests—in other words there is no real
epidermis ; while in Riccia (Crystalworts), on the other hand, a clearly-
defined epidermis, but without stomate, is always present upon the upper
surface of their flat, often deeply-forked, thalloid stems. In the Mar-
chantie (Marchantia, Lunularia, Fegatella, &c.) the thallus not only
presents upon its upper surface a very distinct epidermis, but an epi-
dermis provided with stomats, the guard cells of which, in many cases,
being more than usually complex, owing to the repeated bipartition of
the original mother cell of the stoma-bounding group.
In the true Mosses (Musci)—but excepting the Sphagnums—the
leafy plant of the first or sexual generation has, as a rule, ho properly
30 STUDIES IN MICROSCOPICAL SCIENCE.
differentiated epidermis, the outer or boundary layer, or layers, of
cells (in the stem) being merely smaller, thicker-walled, and more
elosely packed than the inner or axial cells. It is not until the moss
plant enters upon its second stage, or spore-producing life period, that a
distinct epidermis (furnished by the way with peculiar stomatz), makes its
appearance, and then only upon the developing spore fruit.
In Sphagnum (Bog-mosses) the stem is provided with a very con-
spicuous epidermal tissue-system, composed, in some species, of only a
single layer of cells, but, in others of two or four such layers. The cells
are large, colourless, and thin walled and contain either air or water.
The frail walls are generally strengthened by slender, spirally arranged
thread-like thickenings, while in many cases the cells are in direct com-
munication with one another, and with the outside by means of minute
pores. It is up this tissue, as through a sponge, that the water rapidly
passes, and within this tissue, also sponge-like, that water is retained by
these bog-loving plants. .
In the two groups lying above the mosses—that is, in the VascuLaR
CryprocaMs and PHANEROGAMS—an epidermis is an invariably occurring
structure, clothing alike the roots, stem, and leaves, and becoming
variously modified under the influence of individual conditions of
vrowth, and by the physiologically imperative requirements of the plant.
In its origin the epidermis of Phanerogams arises, as we have before
seen, from the dermatogen, a structure that makes its appearance at an
early stage in the plant’s embryonic development. As it gets older, the cells
become more or less flat, while whatever changes may take place in their
outer or exposed walls, the radial walls always remain thin and possibly
porous. Simultaneously with these changes certain developments may
take place among its cells, some, as has been before stated, may produce
hairs, while others may become the guard cells of stomate. Hairs are
freely thrown out by the epidermal cells of the roots, and these, wnder
many circumstances, are functionally concerned in the absorption of
water for the benefit of the whole plant. Hairs are also found upon the
epidermis of stem, leaf, and flower, and are utilised for the performance
of the most varied functions ; ordinary hairs seem to be especially pro-
duced to decrease the rate of transpiration, hence exposure to air and
light tends to promote an increased development of these appendages.
Sometimes a hair is a stinging organ, as in Nettle; a digesting organ, as
in Sundews ; a scandorial organ, as in Bramble ; and so on.
When stomatze make their appearance upon the epidermis, they are
invariably situated above intercellular spaces, to which they offer a direct
means of communication with the outer air. They are not formed in
subterranean or subaqueous structures, and their formation seems to be
regulated (in addition to heredity) by retardation of growth, and an
available accumulation of food material: as has been partially proved by
growing in the air branches of certain water plants that naturally grow
entirely submerged. It was found that, concurrently with a slower
growth, and greaterconcentration of food,a ‘number of stomate made their
EPIDERMAL TISSUE. a1
appearance upon the artificial rial leaves. While further, it has been
recorded that stomatz have been found on galls upon the upper side of
the leaf in vine, although normally. they only occur upon their lower
surface. Here the accumulation of food, due to the flow of sap to the
seat of irritation, was evidently the chief factor in the formation of these,
in this case, apparently functionless stomate.
When the epidermis is fully formed, and, if it is subject to aérial
exposure, the outer boundary walls of the cells are often considerably
thickened, sometimes enormously so, as in many leathery leaves like
holly, mistletoe, and the like.
There exists upon the surface of most leaves a continuous, mem-
branous, transparent layer, the cuticle possessing most extraordinary
resisting power, and useful not only for purposes of protection, but as a
check to transpiration, and thus preventing a too rapid loss of water.
Iodine colours the cuticle brown, while oxidising agents and boiling
potash water dissolves it. A resinous or waxy substance, soluble in
boiling alcohol, covers the surface of the cuticle and forms an effectual
protection from the wet.
It would seem that in addition to the function of protection, the epi-
dermal cells perform other and important duties in the economy of the
plant. They store up a reserve of water which, owing to the thinness
of their radial walls can easily pass from cell to cell, thus enabling them
to meet within certain limits any extraordinary demands brought about
by the necessities of transpiration, while at the same time they are also
able, should the necessity arise, to deliver up to the chlorophyll-bearing
cell a quantity of water for purposes of assimilation.
Occasionally the epidermis gives rise, as in the leaves of Ficus,
Begonia, and many Piperacezw, to an inner layer of cells with thin
walls and watery contents. They are functionally concerned in the
storage of water, and are known as aqueous cells.
In the aérial roots of Orchids and Aroids there is, outside the true
epidermis an extraordinary cellular development that completely invests
the root stretching from the extreme tip to its point of insertion in the
stem. This structure has a remarkable power of absorbing water, and is
known as the Velamen.
A transverse section of the aérial root of a species of Dendrobium,
double stained, and well exhibiting this velamen growth, has been
selected as the subject of study under our present heading. Its structure,
together with the structure of the epidermis proper, may be readily made |
out from the accompanying preparation, by working through the follow-
ing instructions. It may be explained that although we are at present
mainly, if not wholly, concerned with epidermal tissue, yet I have not
hesitated to point out the most important features to be observed in other
parts of the section.
3o4 STUDIES IN MICROSCOPICAL SCIENCE.
rest of the cortical cells, all gradation from these cells to larger ones,
where the thickenings are disposed in irregularly disposed bands of vary-
ing thicknesses (reminding one of the parenchymatous cells from the
lower portion of the thallus of Marchantia)—will be readily observable.
Having completed our observations of the minute anatomy of these
remarkable aérial roots of Dendrobium ; and if we now remember that
this genus of orchidaceous plants grow in such situations (that is, upon
trees), where ordinary roots can do little more than merely play the part
of holdfasts : and, if, at the same time, we remember that the plants
affect regions where the warm air is for ever loaded with an abundance of
watery vapour, we can, I think, readily understand how functionally ser-
viceable such aérial root organs as these must prove themselves to be in
the physiological economy of this or similar epiphytal organisms. Spring-
ing from the exposed base of the succulent stem, the green-tipped roots
soon become curved, and eventually freely hang in longer or shorter cords
in the moisture-bearing air. Water, be it rain or dew, is, strictly speak-
ing, scarcely pure, containing as it does dissolved ammonia and various
salts derived from the impurities of the air; and this water, possessing a
varying nutritive value is readily absorbed by the thin-walled velamen
cells until that tissue becomes more or less gorged. The true
epidermis has evidently a merely skeletal function, a cylinder of
strength, as it were, between the two regions of mechanical weakness—
the velamen and_ cortex. Through the very thick walls
of the. cells of this epidermal system the water would
find a slow and difficult passage, but, as we have just seen, the continuity
of these cells is interrupted by the presence of numerous small, isolated
cells provided with pores, and through these the water from the turgid
velamen cells readily and directly passes into the banded cells of the
cortex ; while from these cortical cells the axial fibro-vascular bundle
obtains its supply of water, and this very essential fluid, the bundle, in ~
pursuance of its ordinary duty, will speedily carry upwards into the stem.
D OX
seshntdasorante
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TW Watson del et tith.
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Sieve Tubes & Inber Cells.
Watson & Son Lethe. 93 Ct Charles $¢ Burm :
VASCICULAR TISSUE.
1.—GENERAL STRUCTURE OF A FrBRO-VASCULAR BUNDLE. -
es
A distinctly differentiated tissue-system usually assuming the form of
isolated cords or strands, is commonly found traversing the various organs
of all the higher or leaf-bearing plants lying above the Mosses in the
scale of complexity of organisation. In this group (that is the true
mosses) there appears for the first time an axial string of dense or closely
packed cells, considerably elongated in the direction of the plant’s most
rapid growth, and still further differing from the other cells of the stem
in having their walls regularly thickened to an appreciable extent. Such
a system as this, composed merely of simple fibres, obviously foreshadows
the much more complex, but still exactly equivalent system of fibres,
tubes (or vessels), and cells that make up the histological elements of the
ramifying cords (or fibro-vascular bundles) of the Vascular Cryptogams,
Gymnosperms, and Phanerogams.
In our study of the growing point of Maize, it was therein learned
that during the whole period of its embryonic condition, a plant is made
up entirely of cells ; and that, although at one stage, these cells are to all
intents and purposes exactly similar, so far at least, as outward form or
general appearance goes, yet the individual cells of different groups are
so fully endowed by the strong force of heredity, each with its own
special physiological potential, that different cell-groups are thereby
compelled to develop towards a permanent or mature state, along certain
lines in gradual yet definite stages of growth, resulting at length in the
production of all the different systems of tissue that are so markedly
characteristic of the species to which the individual in question belongs.
Referring to plate 7 we see, for example, in the longitudinal row of
short broad cells marked (7.) an early stage in the development of a
vessel. Subsequently in the life of such a row, the superimposed cells
would become completely fused, and the transverse separating walls be.
come, perhaps, first ruptured, and then probably absorbed while simul-
taneously with this the contained protoplasm would gradually thicken
certain parts of the now long and common wall, by the addition of new
cell wall material, elaborated in the form of bands, spirals, or the like.
Such special tubular structures are clearly of great functional importance,
inasmuch as by virtue of the peculiar mode of thickening, not only is
there a considerable gain of strength, but the thin or unthickened portions
of the vessel-wall permit, at the same time, an easy passage of gases in
a lateral direction.
36 STUDIES IN MICROSCOPICAL SCIENCE.
A fibro-vascular bundle is made up of two distinct portions—the xylem
or wood, and the phloéra or bast; but while differing considerably from
one another, both histologically and functionally, each region is neverthe-
less typically made up of fibres, vessels and parenchymatous cells.
The vessels, however, present the chief differences, as, while in the wood
these structures, as we have just seen, are completely open or continuous
throughout, and secondary thickenings are freely deposited upon the side
walls ; in the vessels of the Bast, the elements retain to a greater extent
their cell individuality, owing to the non-destruction of their transverse
partitions ; at the same time the walls show little tendency to become
thickened, while numbers of minute pores are found upon either the end
or side walls permitting direct inter-communication between the proto-
plasmic contents of the entire ‘ vessel.”
In all the vascular cryptogams, excepting the Hquisetacew, the
bundles are concentric, that is the xylem is entirely.surrounded by bast ;
while in the Equisetums and in most Phanerogams the xylem and bast
are radially disposed with respect to one another, the xylem being towards
the centre and the bast towards the circumference as in Fig. IL. in the
accompanying plate. Such bundles are known as collateral.
Collateral bundles may be open, as in typical Dicotyledons, where a
region of cambium separates the woody from the bast portion; or the
bundles may be closed, as in Monocotyledons, where no such generative
layer exists. In afew Dicotyledons two regions of bast are present,
one in the usual position, or on the circumferential side of the wood,
and another on the inner or axial side. These have been called bzcol-
lateral bundies. In the subject of our last study (the aérial root of an»
orchis), it was incidentally observed that the xylem and bast of the axial
bundle were therein arranged alternately, that is, in different radii ;
this arrangement is (with very few exceptions) universally characteristic
of roots, and such bundles are known as radial ones.
In the subject of our present study—a preparation of the transverse
section of the stem of Cucwmzs—it will be found that the elements of
the bundles are arranged in a bicollateral manner, and hence in this
respect the cucumber is an exception among the rest of its class. With
the view of obtaining a general notion of the structure of a fibro-vascular
bundle and its position and comparative histology with respect to the
other tissue elements of the stem, the accompanying preparation may now
be examined, according to instructions given below, and sketches made
of the various systems and groups of tissue as they appear under the
different magnifying powers used.
The following characters may be made out with the simple lens :—
(a.)—The somewhat irregularly waved outline of section ; the lobes
agreeing with the distinct ridges that run parallel with the
direction of growth in the stem; the hollows with the corre-
sponding grooves or channels.
(b.)—The epidermis consisting of a narrow line, just slightly
darker than the immediately underlying tissue.
(c.)—The hypoderma, a dark band of closely packed cells, separated
from the epidermis in the ridges by a depth of thin-walled
parenchymatous cells, but actually touching it in the channels,
VASCICULAR TISSUEF.—SIEVE-TUBES. oe
(d.)\—The jibro-vascular bundles arranged in two groups or systems.
An outer sub-circle corresponding with the ridges, and an inner,
corresponding with the channels, ach is seen to be made up
of (1) a middle region—the xylem or wood, composed of empty
tubes (two at least of which are exceedingly large), intermixed
with and radially surrounded by groups and masses of narrow-
celled and denser tissue; and (2) end regions (peripheral
and central)—the phloém or bast—of narrow tubes, many
of which apparently contain some homogeneous contracted
_ material, and presenting a dotted appearance in consequence.
Examine the section again, using an 1 inch obj. power. Make out :—
(.)—The epidermis, a single row of small, but otherwise not very
distinctly marked cells.
(c.)—The hypoderma, of narrow cells, with thickened walls.
(d.)\—The jibro-vascular bundle (1) the thick-walled narrow fibres,
and the thin-walled, small parenchymatous cells, together
with the large and small vessels of the xylem. (2) The vessels
of the bast, some with contracted contents ; others presenting a
circular plate continuous with the inner walls of their respec-
tive tubes; intermixed with these vessels are narrow, thin-
walled, parenchymatous cells ; while true bast fibres appear to
be entirely absent.
Examine bast region under a higher power—say a } or an } obj.—
and carefully observe the structure of the circular plates
noticed in the vessels under the lower power: they are thickly
pierced by minute pores, and present a characteristic appear-
ance, hence their name (szeve-plates).
Oblique and longitudinal sections of the stem show, that the very
wide tubes of the xylem are dotted vessels, the walls of which are
additionally strengthened by banded, irregularly-meshed, thickening
layers ; while the smaller tubes are seen to be spiral vessels.
2.—Bast (PaHtoim)—Sigeve Tupes anD Liper CELLS.
The bast, or phloém portion of a fibro-vascular bundle is, as we have
before seen, typically made up of vessels, thick-walled, elongated cells,
and succulent parenchymatous cells. In form, the elements of the
vessels are usually prismatic, with either slightly oblique, or truncate
ends. The walls are invariably composed of pure or unmodified
cellulose, and are never thickened to any considerable extent. Certain
of the walls (the transverse ones in cucumber) are further characterised
by the possession of pores, through which pass connecting threads of
protoplasm (Fig. 5)1. A peculiar albuminous thickening, known as the
callus, covers the surface of the sieve plate during the active period of
the “tube.” This is also shown in Fig. 5. A parietal layer of proto-
1The continuity of the protoplasm can be well demonstrated by following the
directions given by Sacus. ‘‘It is sufficient,” he says, ‘‘to saturate thin longitudinal
sections of the phloém with iodine-solution until the contents of the sieve-tubes
begin to turn brown, and then to add concentrated sulphuric acid ; this dissolves
the cell-walls and the substance of the sieve-plates, and nothing is left but the
mucilaginous contents coloured a deep brown.” (See Fig. 6),
38 STUDIES IN MICROSCOPICAL SCIENCE.
plasm will persist for a longer or shorter period. With its disappearance
all activity will cease, and the tube become passive or dead. Although
a nucleus is not ordinarily observable, yet in the Scotch fir (Pinus
Sylvestris), according to Russow, several nuclei exist, when the elements.
are ina young stage. In addition to the protoplasm, sieve-tubes also
contain a watery fluid, a sort of peculiar mucilage and starch grains.
In Dicotyledons, where the bast is developed from the cambium,
when a cell is cut off that is destined to take part
in the formation of a tube, it first divides longitudinally, and while
one of the twin daughter cells evolves into a tube element without
further division, the other becomes the mother cell of several bast
parenchymatous cells. The row of cells marked (s) in Fig. 2 are young
sieve-tube elements. According to JANczEWSKI, a number of symmetrical
dots or “ warts” of callus substance make their ‘appearance upon the
transverse walls, the wart material spreads, until, by the coalescence of
the approaching borders, it cover the whole surface of the plate, after
which the pores are formed at pointsagreeing with the position of the warts.
The complete life history of a sieve-tube may be divided into four
periods—(a) the evolutive, during which the vessel is acquiring its dis-
tinctive characters ; (0) the active, within which it attains its fullest
vigour—it contains protoplasm, mucilage, and starch, and performs very
important physiological work ; (c) transitional, during which period it
loses its protoplasmic contents, while at the same time the callus begins
to disappear also; (d) passive, when the tube is empty, and
the plate, viewed from above, has merely a recticulated appear-
ance (as may be seen in the lower part of Fig. 7). In Dicotyle-
dons, where, owing to the activity of the cambium new sieve-tube
elements are periodically cut off, the changes just indicated may take
place in a few months ; but in the closed bundles of the Monocotyledons,
on the other hand, where the sieve-tubes are formed from the procam-
bium, the activity of the elements may continue for years—indeed, as
long as the life of the bundle itself.
In the Vascular Cryptogams, the sieve-tube elements are compara-
tively small, being, in fact, no larger than the neighbouring paren-
chymatous cells. It appears, so far as present research goes, that the
‘“‘ nores” are not actual openings but simply pits, and that they occur
upon both lateral and terminal walls. In Gymnosperms, as represented
by the Scotch fir, the elements are square or longer tangentially. The
radial and end walls present irregular thickenings, and lying within these,
upon the weaker walls, are the sieve pores, here however actual open-
ings. The Monocotyledons have the pores upon the lateral walls only
of the tubes, while the Dicotyledons may have them upon either of the
walls—lateral or terminal.
Respecting the cells of the bast, little requires to be said—In Fig. 8,
the elongated, thick-walled, pliable liber cell is shown, while Fig, 9,
which represents the cut ends of a group of such fibres, displays the
characteristic stratification of the thickening layers. In Fig. 2 they are
shown at (7). The “middle lamelle” may in some cases be lignified,
while in other cases it may be mucilaginous. We havealready seen that
a system of thick-walled liber cells or hard bast is absent in our type-
plant—the cucumber.
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VASCICULAR TISSUE.—WOOD VESSELS AND CELLS. 39
3.—Woop (XyiEM). Woop VESSELS AND CELLS.
The Wood or Xylem of a fibro-vascular bundle, is, like the bast portion,
made up of vessels, thick-walled elongated cells, and cells of a parenchy-
matous nature. The vessels form long and, usually, continuous tubes,
developed, as hereinbefore described, from rows of superimposed and
histologically distinct cells, containing nucleated protoplasm, and bounded
by excessively thin walls formed of pure or unmodified cellulose. In
the ordinary course of development the transverse partitions eventaally
disappear, while the lateral walls of the completely fused cellular elements
are, in part, thickened by the deposition of new cell wall substance in
the form of spirals, bars, hoops, reticulations, and the like. These
secondary deposits are gradually built up as the growing point lengthens
and new cells are added to the forward extremity of the primary vessel-
row. The markings first make their appearance at the lower end, that
is, the end further removed from the apex of the axis, as is shown in
Fig. 2 (plate 10), which represents a portion of the margin of a fibro-
vascular bundle of the common bracken fern, seen in longitudinal section
at a spot where, it will be noticed, the parietal thickenings are just
making their appearance at the distal end of one of the younger ele-
ments of a spiral vessel. Simultaneously with these structural changes,
other changes of a distinctly chemical nature arise within the substance
of the cellulose cell wall, that give, in this relation, a very distinct
character to the xylem or wood vessels.
While pure cellulose is easily dissolved by concentrated sulphuric acid,
or by an ammoniacal solution of copper oxide, the material forming the
Solid portions of the woody tissue remains entirely unaffected when
subjected to the influence of these chemical re-agents. This cellulose
modification—known under the name of Vasculose—may, however, be
readily dissolved by the application of any oxidising substance, such as
nitric acid, chlorine water, or permanganate of potash. Vasculose differs
chemically from true cellulose in containing more carbon and less hydro-
gen and oxygen than that well-known carbo-hydrate.
This chemical metamorphosis of cellulose into vasculose is, however,
an important one, and has a direct influence upon the physical character
of the bundle, inasmuch as the formation of vasculose gives considerable
additional rigidity and strength, or power of resistance, to the stem or
other organ through which the vascular bundles ramify.
A typical group of vessels is shown in Fig. 4, wherein it is seen that
vessels in the same bundle not only differ in appearance, but also in size,
and that they are intermixed with elongated thick-walled cells—the pros-
enchyma. One of the vessels—the largest—is dotted, the ‘‘ dots,” of
course, representing the thin, or unthickened places on the cell walls.
Two have spiral markings, while two others—the nariowest—may be
described as ‘‘ annular,” the secondary deposits having here taken the form
of rings.
40 STUDIES IN MICROSCOPICAL SCIENCE.
eee
The preparation sent out herewith—a longitudinal section (double
stained)—of the stem of a Sunflower (Helianthus annuus), typically and
clearly displays the’ minute structure of the xylem of a fibro-vascular
bundle. (See Fig. 1).
In the cucumber—the subject of our last study—it will be remembered
that the fibro-vascular bundles were absolutely destitute of true bast
fibres, while in the subject of our present study the hard bast (as this
region is commonly called) has, on the contrary, attained an almost extra-
ordinary development.
We will find it therefore instructive to examine in the accompanying
section not only the xylem portion of the bundle (with which we are at
present more particularly concerned), but also the region of the bast,
and especially the hard bast ; while, at the same time, it will give us
an opportunity of observing all the various tissue elements of a fully
developed stem, as displayed in longitudinal section. The student will .
- further find it extremely interesting to compare this vertical section with
that of the growing point of the root of Maize, described in the present
chapter, under the heading “ Primary Tissue.” In this latter preparation
the epidermis, cortex, fibro-vascular system and pith are shown in their
primitive or rudimentary state, while the preparation about to be exam-
ined displays these systems of tissue in their fully developed or mature
condition. It will, of course, be understood that the layer of cambium is
a region of persistent meristematic cells, or cells that have not yet passed
over into a permanent or specialised form ; that each cell in this layer
also possesses the primitive power of multiplying itself by bipartition,
and that from the new cells generated in this way fresh layers of bast are
evolved on the one side, and additional layers of wood or xylem elements
on the other.
The following points of structure will be readily made out in the sec-
tion. It will be well to examine the preparation first under an inch obj.
power, and then under a “quarter” or an “ eighth ” :—
(a.)—The epidermis (slightly green-stained) with scattered uniserial
hairs seated upon multicellular sockets.
(b.)—The cortex (stained carmine), the parenchymatous cells of
which are thin-walled, and of different shapes and sizes, but
all are more or less elongated in the direction of growth of
the stem.
(c.)—The hard bast (green-stained) very strongly developed, and
made up of comparatively wide and moderately thick-walled
cells, with obliquely pointed ends, exactly fitting into one
another, and forming a dense tissue of closely-set cells.
(d.)—The soft bast (stained carmine), composed of sieve-tubes with
thin walls, and contracted granular contents, together with
much elongated parenchymatous cells.
(e.)—The cambium cells (which have also taken up the carmine
stain), lying on the inner side of the soft bast, and made up of
VASCICULAR TISSUE.—WOOD VESSELS AND CELLS. 4]
long but very narrow and extremely thin-walled cells, filled with
protoplasm; the cells lie in radial rows, while the rows are
arranged longitudinally in tiers.
(7.)—The aylem or wood (stained green) made up of wide dotted
vessels towards the cambium and narrower spiral vessels towards
the inner side: intermixed with these are seen long, narrow,
thick-walled tapering cells (prosenchyma ).
(g.)—The pith (stained carmine) formed of irregularly shaped cells,
varying very much in size and apparently empty.
Respecting the vessels noted above under (/) it should be observed
that the transverse partitions indicating the boundary between superimposed
cells may be very clearly seen in all the vessels displayed in the section.
In this case the end walls have only suffered partial absortion, and are
interesting as being forms of vessel somewhat transitional between simple
cell fusions and wood vessels proper. They also demonstrate (on being
compared with similar primary tissue cells out of which the vasicular
system was evolved) that during the formation of the first-formed
fibro-vascular bundle all the cellular elements were lengthened to a
considerable extent, and further, that as the first formed vessels arise
towards the pith, and as therefore the parietal thickenings would be
deposited therein before such vessels had attained their full length, the
spirals have, to a certain degree, been pulled out under the influence
exerted at that time by the stretching walls of the then growing vessels,
- A transverse section of the Sunflower (and double stained) should either
be made or procured by the student, and compared, first, with the longi-
tudinal section of the same plant, and, second, with the preparation of a
transverse section of Pinus Sylvestris, previously distributed with the
present series of “Studies” (slide No. 2, plate 2).
Tn a transverse section of the stem of the Sunflower each fibro-vascular
bundle is seen to be made up of a large patch of hard bast (often sub-
circular in form), to the inner side of which lies a much smaller region
of soft bast, with its convex outline lying against the narrow band of
brick-shaped cells of the cambium. The xylem displays towards its outer
side a closely grouped assemblage of prosenchymatous cells (Fig. 3), and
vessels presenting a concave surface towards the cambium, and sending
rays of wide-tubed vessels among the parenchymatous wood cells that
form the principal constituents of the bundle towards its inner side.
In the transverse section of the young shoot of Pinus (and it would
be well to examine also a longitudinal section of the same), it will be
observed that with the exception of a narrow region of spiral vessels
bordering upon the pith, all the rest of the Xylem portion of the bundle
is made of prosenchymatous cells, which, in longitudinal section display
“bordered pits” upon their lateral walls (Fig. 5, piate 10). When the
thickening process sets in, in these cells, comparatively large circular
areas are left at different points on the walls, but invariably at spots
opposite to one another, in neighbouring opposed cells. As the thick-
42 STUDIES IN MICROSCOPICAL SCIENCE.
ening proceeds, these areas are in time spanned by an all but closed in
dome roof, owing to the pushing over, as it were, of the thickening
material, until when growth ceases, a small circular. opening only is left
facing the interior of the cell. The thin double wall of each unthickened
area is eventually absorbed, and direct communication is thus established
between all the cells of the bundle ae: 6).
EXPLANATION OF PLATE 9.
Fig 1. T.S. of the stem of Melon, showing the concentric arrangement
of the collateral fibro-vascular bundles (mag.) (Le “Maout
and Decaisne ).
L. S. of portion of a fibro-vascular bundle of Ricinus, showing
(c) cambium, (s) row of cells that will afterwards develop.
into a sieve-tube, (p) bast-parenchyma, (f) bast-fibres, (c. p. )
cortical parenchyma, (7) portion of vessel of the wood
(Sachs ).
» o& L. 8. of phloém of Cucurbita Fepo, showing two young tubes
(with contracted contents), and a single ‘tube (to the left),
with sieve-plates in course of formation (Sachs).
Sieve-tube of Bryonia dioica in longitudinal section (Thome ).
L. 8S. through a transverse partition-wall of the gourd, showing
the callus and the connecting threads of protoplasm (Thomé ).
,, 6. Preparation from a sieve tube of cucurbita after solution of the
cell wall with sulphuric acid (Sachs).
» 7. Sieve-plate viewed from above ; upper part represented as being
in an active condition ; lower portion as being in the passive
state (Thome),
, 8. A thick-walled bast cell (fibre).
, 9. I. 8. of a group of bast fibres.
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EXPLANATION OF Puate 10.
Fig. 1. Radial longitudinal section of stem of Sunflower (a) cambium
[with a sieve-tube to the right], (>) wood-fibres, (c) small,
and (d) large spiral vessel, (e) pitted vessel, (f) pitted
vessel in course of foriianor After PRANTL,
Longitudinal section of the margin of a principal -vascular
bundle of common Bracken Fern (Pteris Aquilina) at the
place where the thickening layers begin to appear in the
spiral vessels. After HormuistEr.
,, o. Transverse section of wood cells of young stem of Sunflower,
showing ‘‘ middle lamella” and thickened portions of wall.
After Sacu.
' 4, 4. Longitudinal section of stem of Italian Reed, the cortex lies
towards the right of the bundle, and the pith towards the
left. After CARPENTER.
Detached woody fibre of Pinus showing the bordered pits,
Longitudinal section (somewhat diagramatical) of wood of
Pinus showing the nature of the “pits.”
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T.S. PETIOLE OF LIMNANTHEMUM.
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Watson & Son Lt 93.6¢ Chocrles S¢ Furm?”
FUNDAMENTAL TISSUE.
“Fundamental” is a term which has been applied to all permanent
tissue, not referable to either of the twosystems we have just been study-
ing—epidermal or vascicular. In its simplest form—such as we find, for
instance, in the accompanying preparation—it consists merely of thin-
walled parenchymatous cells, functionally useful in the conveyance of
assimilated material from one part of the plant to another, and for the
storage of starch and such like reserve material in organs that are destined
to enjoy a biennial or perennial existence. As this system forms a ground
tissue through which the isolated fibro-vascular bundles ramify, it is, in the
stems of Dicotyledonous plants, generally separable into three regions—
the pith or medulla, cortex and medullary rays. So far as their compara-
tive extent of growth is concerned, these regions vary very much in differ-
ent plants. Compare, for example, the smallness of the pith and the wide
region of cortex in the section about to be examined, with the thick pith
and narrow band of cortex as displayed ina transverse section of the sun-
flower—and the exceedingly narrow medullary rays in Scotch fir, with
the broad ones so clearly seen in the section of the stem of the cucumber.
In roots—as typically displayed in dendrobium—owing to the axial
position of the fibro-vascular bundles, the pith is never large, while even
that, small as it is, is subject to complete obliteration if the roots even-
tually increase very much in thickness.
In most leaves the fundamental tissue is largely developed, while the
cells contain an abundance of chlorophyll, and are therefore functionally
different from those to whose contents light cannot readily penetrate.
In aquatic plants, the cells of the fundamental tissue are not so closely
arranged as in those of the various land plants, sections of the stems of
which we have already examined. In all the aquatics, large or small
intercellular spaces, bounded by plates of cells, are invariably left in the
ground tissue, thereby providing a convenient receptacle for the storage
of air required either for purposes of respiration or to give buoyancy to
the various organs of the sub-aqueous plant.
The subject of our present study is a transverse section of the petiole
of a species of Limnanthemum, logwood stained, and drawn under a
magnification of 75 diameters. It is selected to illustrate unmodified
44. STUDIES IN MICROSCOPICAL SCIENCE.
fundamental tissue, intercellular spaces and idioblasts. Limnanthemum
is an aquatic genus of exotic plants belonging to the same family as our
own bogbean and gentians. The petioles are long, slender, alternate and
submerged, and carry round heart-shaped leaves, and umbellate heads of
small, regular flowers.
The following points of structure may be observed in the section :—
(a) The epidermis of small, thin-walled cells scarcely differing
(except in size) from the underlying cortical cells.
(Lb) The vascicular system made up of four closely arranged axia}
bundles, each presenting the cut ends of several wide vessels
(spiral vessels as may be seen in longitudinal section) sur-
rounded by cells, the walls of which are thin and un-
lignified.
(c) The fundamental tissue consisting of (1) a small region of pith >
(2) short but comparatively broad medullary rays; (3) the
bundle or plerome sheath' a distinct hoop or line of cells,—thin-
walled and containing grains of stareh—running round the
axial vascicular system, curving over the convex outer
end of each fibro-vascular bundle and dipping into the
medullary rays between the bundles ; (4) the cortex composed
of an outer deep region, and an inner narrow region of closely
arranged sub-globular, thin-walled cells, and a wide breadth
lying between these, where the cells are disposed in radially
long and tangentially short reticulated rows, kept apart by the
existence of comparatively large intercellular spaces.
(/) The édioblasts (or internal hairs) isolated, stellate cells scattered
throughout the intercellular region of the cortex,
It will be noted that the petiole of Limnanthemum being a submerged
organ, it is in consequence not subject to the trying and ever-varying
vicissitudes of a sub-aérial life, and that, as might be expected, a func-
tional epidermis is found in this preparation to be all-but entirely absent.
It will be also noted that the position of the fibro-vascular system -in
the petiole of this plant is similar to that observed in roots (compare with
Dendrobium), that is, it is axial ; and that still further, as in roots, there
is a distinct plerome sheath enclosing the vascicular system. In common
bogbean (Menyanthus) above referred to each bundle is enclosed in a
sheath, a point of structure in which it departs from typical Dicotyle-
dons, but which is very characteristic of Ferns, and perhaps the majority
of all other vascular cryptogams.
1This point of structure is, unfortunately, not clearly shown in the accompanying
drawing.
FUNDAMENTAL TISSUE. 45
In our type, as in water plants generally, we find a very poorly
developed prosenchymatous system ; but remembering that functionally
the woody fibres are concerned, first, in giving mechanical support to the
plant ; and second, in conveying water from root to leaf, the non-
advantage of lignification in these tissue elements in the water-covered
organs of aquatic plants is, of course, easy to fully understand.
The fundamental tissue, or rather, perhaps, certain regions of it, in the
majority of land plants are subject to many adaptive modifications, the
exact nature of which is, or has been, determined by the external conditions
to which the plant or its progenitors have been subjected. For example,
in the long succulent, rapidly growing stems of cucumber, a clearly
differentiated cylinder of thick walled cells (the hypoderma) forms in the
cortex (as we have previously seen) a region of strength in the otherwise
weak and generally soft-celled leaf-bearing axis. Similar hypodermal
regions are very common in stems, and’ we may mention the well-
known meadow-sweet as a good example wherein this modi-
fication of the fundamental tissue system is tolerably well represented.
In some cases the modification reaches extreme limits, as is exemplified
in the formation of such hard tissue as the fruit-stones of plums, cherries,
and the like. Such intensely strengthened tissue is known as scleren-
chyma.
A modification of the fundamental tissue of a totally different nature
is characteristically displayed in the transverse section of the stem of
cucumber (slide No. 9). If the isolated groups of cells lying within the
circumferential ridges of this preparation, referred to in paragraph
(c) in the table of instructions given on page 36, are carefully
examined under a high magnifying power, it will be discovered
that the description of “thin-walled,” as therein applied to the cells,
is, at best, only partially accurate, as, by a proper adjustment of the
light, it will be observed that the angles formed by the meeting of the
lateral or longitudinal walls are filled with a clear-looking, finely
striated thickening material, the presence of which reduces the cavity of
each cell to an almost circular form in sectional outline. This special
kind of tissue is known as collenchyma, it possesses the power of
swelling to a greater or lesser extent by the absorption of water ; while
functionally it is concerned in giving strength and a considerable degree
of elasticity to the organ within which it is generated. The cells are,
generally speaking, moderately long ; they are filled with sap, and con-
tain either only a few grains of chlorophyll or none at all. The cell-walls
may be coloured a bright blue by submitting sections to the action of
chlor-iodide of zine.
Although the occurrence of collenchyma is comparatively rare in
Monocotyledons, yet it seems to be generally present in all the climbing
species, such as Smilax, or that commonly cultivated Chilian plant with
crimson flowers and edible berries—Lapigeria rosea.
46 STUDIES IN MICROSCOPICAL SCIENCE.
——$ +
The function of the intercellular spaces in Limnanthemum has been
already referred to, but, for the sake of comparison, we may here again
direct attention to the intercellular spaces in the stem of the Scotch fir.
As has been already stated on page 11, the intercellular spaces in this
plant take the form of canals, and act as receptacles for the resin secreted
by the cells that form the walls of these canals.
In the Umbelliferz we find intercellular spaces, containing a mixture
of resin and gum, while in other cases—the water plantain (Alisma),
for example—the canals are receptacles for a kind of latex.
In the fundamental tissue of the leaf, intercellular spaces occur that
are placed in direct communication with the atmospheric air through the
medium of those important epidermal intercellular spaces—the stomata.
Finally, with respect to the idioblasts (Sacu’s term for “individual
cells in a tissue otherwise homogeneous” that ‘ become developed in a
manner strikingly different from their neighbours”), we have seen that
those in Limnanthemum bear a striking resemblance to hairs—hence
their special name of ¢richoblasts. As examples of other forms of
idioblasts we may refer to the /¢thocysts—comparatively large cells, con-
taining clusters of crystals (cystoliths)—typically displayed in the hypo-
dermal cells of the leaf of the Indian-rubber tree (Ficus Elastica) or to
the laticiferous idioblasts as exist in the tissues of Spurges (Huphorbia)
and other plants.
Set, 2. LFlate le
——r}
E|D del ad’ nat TW Walson diel, et bith
TRANSVERSE SECTION STEM OF MAPLE.
Shewmg annual wings.
Kaos
Watson & Son ath 93, 6*lharles S¢ Bom
SECONDARY TISSUE.
In all perennial structures, provided with open fibro-vascular bundles,
fresh growths annually arise through the persistent activity of the meris-
tematic cells of the cambium. These secondary layers of wood and bast
may be observed in almost any woody-stemmed Dicotyledon, but a three-
year-old branch of the common Maple (Acer Campestre), in transverse
section and double stained, has been selected asa typical example of such
secondary increase in thickness.
_ Early in the history of the branch, and while it was yet in the bud
stage, the first-formed or primary bundles arose directly out of the meris-
tem of the apical region, after the manner previously described herein.
These bundles were of course open, and the layers of cambium lying
between the regions of wood and bast (fascicularcambium) were connected
by similar plates in fundamental tissue (interfuscicular cambium) so as to
form a complete cylinder of active meristematic cells. As the bud
lengthened into a branch its axis increased in thickness through the
additions made to it by new cell formation in the cambium.. Fresh
layers of wood and bast were formed by the interfascicular as well as by
the fascicular cambium, and as a consequence the primary wood appears
as so many processes outstanding in the pith, while the primary bast
bundles get more and more widely separated from one another, as they
are outwardly pushed by the thickening stem. One histological difference
between the primary and secondary wood is that in the former the vessels
are spirally marked, while in the latter they are deeply pitted. Owing
to this difference the cylinder formed by the primary system is
descriptively known as the medullary sheath.
During the later weeks of the growing season, and when vital energy
is on the wane, there is a marked difference in the size and diameter of
the xylem elements, therefore, when, in the next returning Spring, the
cambium again becomes active, the comparatively large and normal tissue
elements stand out conspicuously beside the dwarfed growths of last
autumn, so that a clear and well-defined boundary marks the line where
one year’s growth ends, and another begins.
Furthermore, in structures that are destined to withstand subserial
exposure for years, the ordinary epidermis is early replaced by a more effi-
cacious protective layer of squarish cells (cork ),containing (when mature)
nothing but air, and whose walls have suffered a characteristic moditica-
tion. The material (swberin) of the cell-walls, while being very elastic
and extensible, is most resisting, standing, as it does, without solution,
the action of concentrated sulphuric acid. Water also is unable to pass
through it. Physically and chemically, therefore, cork is eminently
fitted to act in the capacity of an external protective tissue.
Before examining the section it will be well to procure a twig of Maple
and make a few careful observations with the naked eye. Selecting there-
48 STUDIES IN MICROSCOPICAL SCIENCE.
fore a bit of a three-year-old twig, it will be seen that, externally, it is
covered with a dry, dark-brownish flaky ‘‘ bark” with pimple-like excre-
scences (lenticels), scattered pretty freely over its entire surface. Owing
to pressure from below, the “bark” is split longitudinally into narrow
anastomosing bands, exposing an ashen-hued investment beneath. The
lenticels are formed of a collection of loosely arranged cork cells that
take the place and perform, in many young stem structures, the functions
of stomata. By scraping the outer coat away the underlying ashen-grey
layer may be fully exposed. It is a cylinder of cork, papery in texture
and known as the wpertderm. If this layer is in turn care-
fully scraped away, a green layer of a parenchymatous nature may
be easily displayed. Using the knife again, but this time very carefully,
anumber of very fine white threads will be discovered lying in softer
tissueimmediately beneath thelayer of greencells, Thethreadsare primary
bast fibres, and the succulent tissue the soft bast. By continuing the
scraping, broad strands of secondary bast will be exposed that form alto-
gether an almost continuous cylinder, around the stem. This cylinder is
very easily detached from the internal shaft of wood, and when so re-
moved the outer surface of the wood and the inner surface of the bast
present asmooth moist appearance. The moisture is due to the spilt con-
tents of the smashed cells of the tender cambium that lay between. By
cutting the wood away on one side an internal mass of pith may, lastly, be
laid bare.
Turning now to the section issued herewith, the following general
points of structure can be made out with an ordinary lens :—
1.—A central disc of pith (crimson stained), made up of comparatively
large roundish cells.
2,—A broad ring of wood (green stained) clearly marked out, by two
dark, thin- lined circles, into three regions (representing three years
of growth). The dark ground tissue represents the individually
narrow and closely-arranged woody fibres while the clear specks are,
of course, the cut ends of wide tubes, or wood vessels. A dark,
wavy tissue-band lies to the inner side immediately surrounding the
pith.
3.—An external circular band of ‘‘cortex” (stained red), with three or four
narrow, isolated, interrupted hoops (of a greenish-yellow tint) occur-
ring within Te substance. The aie or circumferential layer
(brownish hued) is burst, and shows a tendency to “ peel.”
4,—Numerous slender lines—medullary rays—starting from the pith
and passing through the wood and cortex to the circumferential
layer.
By using an l-inch obj. the following particulars can be made out with
respect to the various systems of tissue :—
1,—The pith of roundish or polygonal cells becoming larger and laterally
compressed towards the circumference.
SECONDARY TISSUE. 49
2.—The wood or xylem system made up of densely packed, narrow cells
(woody fibres) interspersed with isolated or associated (in twos,
threes, or even fours) wide tubes or wood vessels. The woody pro-
cesses (primary xylem) that are pushed into the pith and the boundary
lines between the annual growths are formed, as will be seen, of
much narrower tissue elements than those found in the rest of the
same system.
3.—The cambium represented by an often contorted (becoming so during
manipulation) band of cellular tissue that has taken up very strongly
the carmine stain ; the outline of the individual cells may be per-
haps just made out in parts where contraction has not taken
place.
4,—The cortex (so named here for convenience) made up of (a) hard and
(b) soft bast, (c) green layer, (d) younger or inner, and (e) older or
outer layer of cork.
(a.)—The hard bast, comprising an outer series of green-stained
patches (the primary hard bast) concentrically arranged, and
three inner greenish or yellowish-stained more or less continuous
circles.
(b.)—The scft bast of thin-walled, carmine-stained elements, in
which the interrupted hoops of hard bast are imbedded.
(c.)—Green layer of rather larger and tangentially compressed cells,
the chlorophyll of which has been dissolved out, and the walls
and contents carmine stained.
(d.)—-Younger suberous layer composed of rectangular cells, the
walls of which are slightly stained with green.
(e.)—Outer suberous layer made up of irregularly compressed or
contorted cells passing into an amorphous brownish superficial
layer of varying thickness.
5.—The medullary rays, some (the primary), commencing at the
circumference of the pith, others (the secondary) commencing in
the wood of the second and third year.
Under a quarter-inch obj. the following details may be observed :—
1.—In the pith, clusters of starch grains may be discovered in some of
the cells, but in the cells of the two or three outermost layers of all
(which are roundish in outline, and have taken up the green stain,
appearing therefore under a low power as belonging to the xylem
system) starch grains completely fill up the cell-cavities.
2.—In the azylem system may be noticed the difference in diameter and
outline between the woody fibres in the primary and secondary
crowths, in the regions marking the boundary between the annual
layers and in those touching or bordering upon the vessels.
3.—In the cambium region the thin-walled rectangular meristem cells
may be seen regularly disposed in radial rows, the protoplasmic
contents being stained a deep crimson.
50 STUDIES IN MICROSCOPICAL SCIENCE.
4,—The hard bast elements are displayed as closely set angular fibres,
with walls so completely thickened as to leave an extremely
narrow internal cavity. Faint striations may be distinguished in
the substance of the walls. Compare with fibres of xylem.
5.—In the soft bast the sieve plates of some of the phloém vessels may
be discovered by careful search and focussing.
6.—The medullary rays in the wood are filled with minute grains of
starch. In the bast region they appear to be empty. The indi-
vidual cells are generally larger (at least towards their terminations)
in the bast than in the wood.
7.—The cells of the green layer are large and tangentially elongated
(oval in sectional outline), and their contents are granular and
crimson stained.
8.—The inner suberous layer is made up of square or sub-rectangular
cells, disposed in radial rows. It is clear-looking as the cells are empty.
9.—The outer suberous layer is made up of distorted and disorganised
cells, portions of which are lying on the circumference as brown,
structureless masses.
It may be noted, as points that may be made out in longitudinal sections
of the fresh stem, that the cells of the pith are dotted, and that the
vessels of the primary wood are provided with spiral thickenings, while
those of the secondary growths are closely pitted. The woody fibres run
off to a point by an one-sided slope, after the manner of the
cutting edge of a chisel. The bast fibres are very slender and very
long. The cells of the green layer are a little longer than their greater
breadth, the walls are thick, clear-looking and homogenous. The inner
cork cells are almost square, their walls are thin and their contents are
merely air. Chlorophyll is not only found in the green layer, but it
pervades the cells of the medullary rays, and is even (in one and two
year old twigs) found in the outer starch-bearing cells of the pith.
This preparation will, it is hoped, sufficiently demonstrate the normal
mode of increase in thickness in dicotyledonous stems, by the formation
of secondary vascicular tissue through the activity of cambium. Secon-
dary increase in roots is effected by a similar process of new cell develop-
ment from a layer of cambium cells. There is an initial difference, how-
ever, as to the origin of the cambium. It will be remembered that in roots
the bast and xylen a bundles are arranged radially, and not collaterally as
in stems ; now the cambium from which the secondary vascicular tissue
is generated arises in the parenchymatous tissue behind the phloem
masses only, and very soon, owing to its activity, new or secondary wood
is formed on its inner or medullary side, and secondary bast on its outer,
or against the inner side of the primary phloém. A cambium layer
appears in front of the primary xylem bundles, but this will merely pro-
duce parenchymatous tissue to keep pace with the thickening of the
stem by woody increase. From this date increase in thickness goes on just
as in stems, and the secondary wood may or may not subsequently coalesce
with the primary.
APPENDIX.
—————
SECTION IL.
BOTANICAL HISTOLOGY, :
Ft 5
nes 7 from top, 9 from foot, a 5 from foot ; for ‘‘ stomatae” read “a
| ;
error occurs several times on pages 30 and 31. a
Sie 16 from top ; ; for ‘‘it cover the whole surface” read ‘it covers the J
“7
| 22 from foot ; for *‘ homogenous” read ‘* homogeneous,” ibs By
a
er
=
a
:
.
* «
ee
INDEX.
SECTION II.
BOTANICAL HISTOLOGY.
A
Acer campestris, 47.
Aerial roots, 31.
Agaricus, 19,
Algae, 4, 8, 9.
ty filamentous, 17.
Anigosperms, 28.
Autherozoids, 8.
Apicle Cells, 27.
Apicystis, 9.
Aquatic plants, 43,
Arachnoidiscus Ehrenbergii, 9.
Bark, 48.
Barm, 5.
Bast, 33, 37, 40, 49.
Botrydina, 9
Cc
Calyptrogen, 27, 47, 49.
Cambium, 36, 47, 49.
Cells, 40,
Cell ‘(as an individual, The), 13.
» binary subdivision of, 18.
,, Morphology, of the, 1
,, Rutherford, on the, 3.
,, Schleiden, on the,1.
», Schwann, on the, 1.
Theory (The), 1
Cells (green) 13.
», Protoplasm in, 2.
», Variability of form in, 5.
Cells with Special Contents, 11.
Cellulose, 39.
Chara, 20.
Chlorophyll, 50.
Cladophora, 18, 20.
Closterium, 16.
Collateral Bundles, 36.
Collenchyma, 45.
Conferva, 18.
Cork, 47.
Cortex, 40, 48, 49.
Crown Imperial (Scale- leaf of), 11.
Cucumber, 40.
Cucumis (Stem of), 36.
Cuticle, 31.
Cystoliths, 46.
D
Dendrobium (aerial root of), 31.
Dermatogen, 25.
Desmidiz, 16.
Diatomacee, 9.
Dicotyledons, 28, 38, 47.
Ei
Eleocharis Palustris, 25.
Embryo Cell, 25 (of Maize), 27.
Endochrome, 14.
Epidermal tissue, 29.
Epidermis, 31, 36, 37, 40.
Equisetum, 21.
F
Fern (Prothailus of), 22.
Fibrovascular bundle, 36, 37, 39.
Fritillaria imperialis, ge
Fucus vesiculosus, 7.(Conceptacles of) 8.
Funaria, 20, 22.
G
Gleocystis, 9.
Growing point, 27.
Gymnosperms, 38,
H
Helianthus annuus, 40.
Hormospora, 9.
Hypoderma, 36.
Idioblasts, 46.
Laminaria, 27,
Leaves, 43,
Lenticels, 48.
Liber cells, 37.
Lizhens, 19.
Limnanthemum, 43.
Lithocysts, 46.
Mi
Magenta solution, 6.
Maize, (Root of), 26.
Maple, 47.
Marchantiae, 27.
Medullary rays, 48, 49.
Pes sheath, 47.
Metzgeria furcata, 21, 27.
Micrasterias denticulata, 13.
Monocotyledons, 28, 38.
Morphology of the Cell (The), 1
of the Tissues, 17.
Mosses, 20, 27, 30.
Muscinee, 27.
N
Nitella, 20.
oO
Oosphere, 8, 25.
Oscillatoria, 17.
P
Palmella, 9.
Pasteur’s Fluid, 5.
Pediastrum, 6.
Pencillium Glaucum, 19.
Periblem, 27.
Pericambium, 32.
Periderm, 48.
Petiole of Limnanthemum, 43.
Phanerogams, 25.
Phloém, 37.
Pinus sylvestris, 10, 38, 41.
Pith, 33,41, 48.
Plasmodia, 4
Plerome, 27.
Primary Tissue, 25.
Prothallus of Fern, 22.
Protonema, 20.
Protoplasm, 2, 6, 37.
Pseudo-nodule of Diatoms, 9.
Puncta of Diatoms, 9.
R
Regnum Protisticum, 4.
Root of maize, 26.
Roots, 43.
S
Saccharomyces Cerevisiee, 5.
Scale Moss, 21.
Schleiden on the Cell, 1
Schwann ,, a
Scotch Fir, 38.
Secondary Tissue, 47.
Secretion Cell, 10.
Sieve Plates, 37.
Sieve Tubes, 37, 38.
Sphagnum, 30.
Spirogyra, 18.
Starch Grains, 11,
Staurastrum, 16.
Stomata, 29, 30, 31, 46.
Suberin, 47.
Sunflower, 40, 41.
T
Thallophyta, 27.
Thallus of Lichens, 19.
Tissue, Epidermal, 29.
. Fundamental, 43.
», Secondary, 47.
5, Vasicular, oo:
Tissues vaior of ae 17.
Torula, 4.
Trichoblasts, 46.
U
Umbellifere, 46.
Unicellular Plants, 13.
Vv
Vasicular Tissue, 35.
Vascular Cryptograms, 30, 38
», Phanerogams, 30.
Vasculose, 3.
Velamen, 31.
Vessels, 39.
Volvox, 16.
W
Wood, 39, 41.
9) Cells, 39, 48, 49,
», Vessels, 39, 48, 49.
xX
Xylem, 39, 41, 49.
Popular Mucroscapical Stadves Vol LPMatel.
Aidel.ad nat. JWWatson. del.et lith.
rESBRUDLAN (GN ETS S
Flannan Islands
X 25
Watson & Son. Chromo litheg™! Newhall St, Birm
POPULAR MICROSCOPICAL STUDIES.
HEBRIDIAN GNEISS.
From the Flannan Islands, x 25 diameters.
J. Felspar ; g. Quartz; 2. Hornblende.
On the Hebridian Gneiss of the Flannan Islands, by M.
Forster Happs, M.D., F.R.S.E., Erc., Professor of Chemistry in the
University of St. Andrew’s, Past-President of the Mineralogical Society
of Great Britain and Ireland.
It is always well to begin at the beginning. Sections of several. rocks
will, from time to time, be laid before our contributors ; for rocks, equally
with the petals of flowers, the wings of Insects, and the feathers of birds,
are things of beauty ; do they disclose the
genius of constructive power, the adaptation of means to an end. We
begin at the beginning, that is, with the oldest rock,—the first brick of
the edifice,—the deepest film of the crust of the earth. We know down
through or into that crust for about twenty-eight miles. Not that we
have ever bored a hole nearly so deep as that, or could have gone to the
expense of so doing to supply an illustration; but that convulsions and
elevations and denudations have tossed up, or brought within our reach,
portions which originally lay even so deep down. But, tobe perfectly precise,
it has to be said that the rock which forms the Hebri les, conferring upon
these barren islands their sinuous coast lines, and their rugzed crests,
is not altogether and absolutely the deepest known of any part of the
earth’s surface, though it belongs or pertains to that which is. That
oldest rock is found in the Gulf of St. Lawrence in Canada, and this
rock of the Hebrides is a little higher in the scale—a kind of upper
crust to it. It is so old, however, so deep down, that GeErkiz happily
has called it the “ Floor of Europe ;’ and more happily, and with pro-
phetic prevision, our forefathers commonly, and somewhat jauntily, but
with dignity profound, were wont to speak of ‘‘ Old Scotland ;” and is it
not now generally admitted, that, if not an uneducated man, he is an
2 POPULAR MICROSCOPICAL STUDIES.
undereducated man who does not know that Gaelic was the oldest spoken
language,
‘¢ When Adam first met Mother Eve,
All fresh from Nature’s dew,
The first word that he’ll speak to her
Was Comarashin du.”
And then again had not that great invader, The Fairshon
oD o b 5]
‘¢ A son who married Noah’s daughter,
And almost spoiled the flood
By drinkin up the water ?”
Scotland is indeed so old that, in comparison England is quite a
recent fabrication—a kind of many-coloured geological carpet spread over
Scotland—worn through here and there from its thinness and hasty
manufacture, and disclosing at the bare places some of the old joist-
ing, though no actual foundation stones like this.
Some ingenious gentlemen, who do not hestitate to stretch a point or
two, have connected this old rock of the Hebrides with the rock in Can-
ada, below the Atlantic ;—a stretch of imagination which is quite as
long as the cable itself. While unable to go quite so far as that, we
went as near to Canada as we could, while still keeping a grip of British
land ; away out westward upon the Atlantic, until only St. Kilda, with
its dead and caved-in volcano, stood further.
How few of our readers can have heard of the Seven Hunters or the
Flannan Islands; how many fewer can have seen them! We question
if one has landed on them. And yet here—here, where only at sore cost
in many ways, can we now, under favourable circumstances, plant the
sole of our foot, did the indomitable energy and proselytising zeal of the
Romish faith, generations past, plant a chapel.
There, where no trace of men’s habitation now remains—sole refuge of
the otter and the seal, aud the fowls of the air—do the roofless walls
still stand in testimony, demanding of us, however much we are com-
pelled to differ, that we be magnanimous and just in awarding our re-
spect. Truly, it was a strange home, both for teachers and for taught !
Seven precipitous rocks, some of which can feed a score of sheep, when
they can be got there ; separated some two miles from the others, and all
so far from the nearest land, that it is only the grand hill of Meallashaval
in Lewis, which, with its nineteen hundred feat of altitude, makes that
land visible.
Little could the zealot who there laboured, though stored in full
plenitude with the richness of Rome’s learning, have imagined that when
the first law of “dust to dust ” had swept him and his flock into the
insatiable grave of the forgotten, some chip of the senseless rock beneath
his foot might raise him to remembrance, and bring the scene of his
labours closer to the eye than had his self-sacrifice, and immediately
under the ken of a centre of civilisation mightier even than the mighty
Rome.
Truly might a chip of the rock of the Seven Hunters serve as
the text to a volume on “The Microscope,—its place and power.”
HEBRIDIAN GNEISS. 3
And is there anything very wonderful, or very beautiful about the rock
after all?
Not very beautiful direstly ;—it is not even what would be called ;
handsome rock ;—it seems indeed as do all created things to ‘eae
the great Histinetion between man’s works and God’s works, namely,
. that the more one magnifies or examines the former, the coarser, more
faulty, and uglier they are; while the more we so treat the latter, the
more beautiful, the more wonderful they appear.
As for the wonderful things which the microscope shows in this rock,
neither would this paper, nor this publication suffice to expand them
all; but we will tell what are some that you will at once see.
First, there isa very transparent, glassy, colourless substance; that is
called quartz. It forms the yreater pirt of the crust of the earth ; when
crushed up it forms sand ; and this sand, when stuck together again any-
way, forms sandstone. Then there isa green thing, rather muddy green,
—that is called hornblende, and this is the bneieturiatis mineral of this
kind of rock ;—so it is sometimes termed hornblendic gneiss. Next,
there is a semitransparent, and whitish coloured thing, which is felspar ;
when this is disintegrated down, 1t forms mud, and when melted up it
forms artificial teeth. Now, this is about all that is seen at first sight ;
but, if you take a higher power! and examine the first thing, you will
perceive myriads of minute round spaces, like drops of colourless oil ;
and if you look more closely you will see in the centre of some a small,
round, very brilliant speck. The central speck is filled with a gas which
kills man and beast in the “ Poison Valley” of Java, and feeds plants all
over the world.2 The space round the central speck is filled with the
same thing condensed into a liquid, by a force about as great as could be
given by the blow of a steam hammer.
Now, if you have a polarising apparatus, and examine the green part
of the slide by looking through it, using light whicly has passed through the
lower Nicol prism, you will find that the green colour changes to a kind of
brown if you turn the Nicol. And lastly, if you put into position the
upper Nicol, and examine the thing they make teeth of, you will find it
to be barred and crossbarred all over by a kind of rectangular network of
beautiful colours ; while if you examine it with a high-power, even with-
out the Nicols, you will find it to contain many flat crystals of a great
many shapes, but in which you can generally count six sides. These have
been unhappily called micro-/’ths.—more happily endomorphs.
The meaning of all these things you may wish to work out. To do
this you would require many slices cut in many ways. It is the
common rock of the Islands, and you may go and take enough. Here is
how you can most easily do it, and what it may cost you.
Hire a yacht at Oban, provision her for say three weeks. Go cannily
through the Sound of Harris, as many a craft has met misfortune there ;
YA f-inch objective with an ordinary eyepiece will ap:
? Carbonic acid gas,
4 POPULAR MICROSCOPICAL STUDIES.
proceed to Loch Thamana-bhaidh, as the nearest harbour south of the
Islands, and here lay in a good stock of patience. If it has been blowing
gently for say four days “from W.S. W., make your first venture. Sail
round the islands, examining the spots where your captain says landing
can be made. Probably you tind a surf rushing fifty feet up the cliffs.
Shoull the wind run round to the north, seek h: hour in Loch Carloway,
Loch Roag ; in order to hold a vantage start. Here lay in a second stock
of patience, but hold self and crew ready to turn out, even at the moment
they feel most ready for turning in.
Should it fall “flat calm” when you are within six miles of the islands,
during your next venture, and you feel that you must draw heavily upon
your stock of. patience, do so by all means ; but spice abundantly with
determination, and kee} ) hanging on day and night by the islands, for
your chance is now or Het “fora month, Ifon jumping ashore after
your companions you come down crunch on one knee, you be dragged by
those companions half fainting beyond the sweep of the second surge (the
first has gone over you to the neck ), you lie for a fortnight on the deck
of the yacht with your knee strapped in bandages, and of the colour of
a copper Indian from tincture of iodine, and if you carry a notch in your
kneepan to your grave, still be thankful—you have got your specimen.
You icy have esc aped worse things than a notched kneepan ; especially
if it may have chanced that your pilot was the same as he who had charge
of the Lively when she lately tried conclusions with the Chicken.
How to Prepare a Rock Section for the Microscope.
It is not necessary to procure expensive slitting and grinding machines
for this purpose. In the production of a large number. of sections elako-
rate lnstimments save time and Jabour, but for all ordinary work, such as
the preparation of a dozen sections or so, a few simple tools will be found
quite sufficient. Let us see how we can prepare a good seetion without
the aid of a lapidary’s bench.
The following articles should be procurcd :—Ist. A good geological
trimming haminer and chisel.! 2nd. Two thick zine or lap-metal plates,
each about 12 x 15 inches in surface, also a slab of plate glass of the same
size. 3rd. A Water-of-Ayr stone, or a slab of marble. 4th. Fmery
powder of three kinds—(i.) Oukey’s No. 50 or No. 60 hole; (ii.) Oakey’s
No. 90 hole ; (iti.) Oakey’s finest flour emery. Oth. A few bits of stout
window elass cut into pieces of about an inch square each. 6th. Some
hardened Canada balsam, made by heating ordinary hquid Canada balsam
iia sand or water bath, until on cooling the balsam become as hard as
ice; 1t may be put up in the form of rods of sealing wax. 7th. Canada
iThese may be obtained from My. Russell, 48, Essex Street, Strand, London,
W.C,
HEBRIDIAN GNEISS. 5
SY a
balsam hardened and redissolved in benzol, may be obtained of any
dealerin microscopical specialities. 8th. Glass shps and cover glasses.! 9th,
Commercial benzol.
Ist Process.—Take a chip off the rock. By dint of perseverance, a
tolerably large and thin chip may be obtained with the hammer and
chisel ; or, to prevent mishaps, such as the loosening of any of the com-
ponents of the rock, get a slice cut off by some working lapidary.?
2np Procuss.—Place a little emery, No. 60 hole, on one of the metal
plates, moisten it with water, and by carefully rubbing one face of the
chip or slice with a circular movement from the edges towards the
centre of the plate, the specimen will acquire a flat but rough
surface. If the motion on the plate is not carried on uniformly over its
surface, 1t will inevitably wear the plate into hollows, and prevent the
possibility in future of securing a flat face. Now wash the specimen
thoroughly in water to remove any adhering particles of emery.
3RD Procrss.—Follow the directions just given above on the second
inetal plate with No. 90 hole emery. This will smoothen the already flat
surface of the specimen. Wash thoroughly in water.
47TH Procrss.—Repeat the operation of grinding, on the glass plate
with flour emery, or another metal (pewter) late may be used, The
face ousht now to be perfectly smooth and free from scratches, but to
ensure success, rub it upon the Water-of-Ayr stone, or on the smoothened
marble slab, until the surface is perfectly smooth or even polished.
Should the marble slab or Water-of-Ayr hone become uneven, the
irregularities may be readily effaced by rubbing them flat on similar
slabs with water. It is not absolutely necessary to polish the surface of
the specimen, as the mounting in Canada balsam will overcome any
superficial deficiency, but the surface must be perfectly smooth and quite
flat. Jf it is scratched, the rents so produced may be sufficient to destroy
the specimen in a subsequent process, and if it is not quite flat, that
uniform thickness, which is generally preferred, will be difficult to attain
afterwards.
5rH Procrss.—Fasten the smoothened surface on one of the little
square pieces of glass ; to do this dissolve a little of the hardened balsam
over a Bunsen or spirit flame, on to the glass, and after warming the
specimen place its smooth surface on the balsam ; gently squeeze out the
superfluous medium to the exclusion of air-bubbles, and scrape it clear
with a blunt knife blade. When cold the slice of rock will be found
securely fastened to the square piece of glass.
6rH Process.—If the chip or slice is very thick, its other face will re-
quire to be considerably reduced, and this should therefore be done on the
first metal plate with the coarsest emery (No. 60 hole). When reduced
to about one-tenth or one-twelfth of an inch in thickness, it should be
x
1The beautiful oval cover glasses, now so much used for rock sections, may be pro-
eured from Mr. Aylward, 15, Cotham Street, Strangeways, Mancheste .
2Mr. Turner, of 44, Berners Street, Great King Street, Birmingham, cuts good
thin slices at about 1d. per slice. :
6 POPULAR MICROSCOPICAL STUDIES.
thoroughly washed in water, and still further reduced on the next plate
with finer emery (No. 90 hole) until it is tolerably transparent and of uni-
form thickness throughout.
77TH Process.—Rewash well in water, and progress carefully with the
grinding on the glass plate with fine flour emery. During this process
the section ought to be constantly examined under the microscope until
the desired degree of thinness has been attained, when it may be finished
off with care on the Water-of-Ayr stone or on the smooth marble slab. In
the case of the Flannan Islands Gneiss, the muddy-green material, or
hornblende, ought to appear clearly greenish, and when placed under a
singly rotating Nicol’s prism ought fo be seen to change in colour to a
brownish hue; if the crystals appear black instead of green, then the
section is not thin enough.
.
It is sometimes useful to have both thin and thick sections, but, as a
rule, the sections ought to be transparent enough to enable the observer
to distinguish ordinary printed letterpress through them. The sections
may combine thin and thick parts ; it is always easiest to prepare them -
thus ; to have the edges thin and the central portion thicker, and these
are more useful than uniformly cut sections, where only one specimen is
available. To attain uniformity of thickness, when the centre happens
to be perversely thick, a slightly convex grinding surface, such as a
turned disc of wood or metal, may be used with the finest flour emery,
or with jeweller’s rouge, or rotten stone.
8tH Process.—Pour a little benzol into a saucer, or better still, into a
white porcelain saucer-shaped artist’s palette! Gently heat the square
piece of glass with the adherent section over a Bunsen or spirit flame ; as
soon as the hard balsam has been melted, the section may be removed
with the edge of a penknife into the benzol, and allowed to soak there
for about five minutes or more. A soft camel’s hair brush should be
used as a lifter; with a little care the section, however thin, may be
transferred on to a glass slip into a drop of balsam, and covered in the
usual way with a thin covering glass.
OO ee ee ee ee ee
1These palettes, which are far more useful than watchglasses, may always be pro-
cured from Messrs. Rowney, of 52, Rathbone Place, London, W.
Popular Mucroscopual Studres Vol 1 Plate 2
ap dl adnat J WWatson del e lth
HUMAN SCALP. H. S.
A130.
Watson & Son Uth C+ Charles St Burm
POPULAR MICROSCOPICAL STUDIES.
THE SCALP.
HorizontaL SECTION oF HuMAN SGALP.
DovuBLe STAINED.
x 130 Diameters.
Etymology.—Sealp, or Skalp, ». (Shelp, Schulp, in Dutch), meaning
literally the skull ; cranium ; brain-pan ; also, that part of the integument
of the head usually covered with hair; hence, the skin of the head, or a
part of it, with the hair belonginy to it, torn off by North American
Indian warriors as a token of victory.
INTRODUCTORY REMARKS.
If we lookupontheskin of the head merely as skin, with or without hair
covering it, this is exactly as we ought to do: it is really only integn-
ment, such as is found all over, or nearly all over, the body, under a
modified form. It has all the properties of skin, and its hair has all the
properties of hair, but these are in many ways peculiar. For exainple,
no part of the skin of the body, except that of the head, can be mo ed
upon the parts beneath to any perceptible degree by any mechanism
specially attached to it. If the reader has noticed a fly alight on
the flanks of a horse, ne will have observed the skin of the flank quiver,
and the fly dislodged, The skin in this region has the power of move-
ment, not residing within itself, but a sheet-like, delicate muscle, called
the panniculus curnosus, has the power of vibrating the skin to and fro.
This is so in many quadrupeds. In human beings, there is a muscle
beneath the skin of the head, which can move the skin backwards and
forwards. This is called the occipito-frontalis, because it is attached to
the occiput at the back of the head, and to the frontal bone at the front
of the head. The scalp sits quite loosely upon the bones of the skull,
8 THE HAIR AND ITS FOLLICLES, &c.
with thismuscle between the two. In most people, this muscle is never
exercised, so that it remains thin, and weak, and quite incapable of
drawing the skin of the head backwards and forwards, except to a very
limited extent. The human ear lobes have also two or three little deli-
cate muscles, which man, having his hands always at the ready, never
exercises. Now, with perseverance in their regular exercise, these little
muscles of the scalp and the ears can do their work very efficiently,
indeed. ‘The writer has seen an old Edinburgh professor, who used to
insist that most muscles were under the control of the w///, if one liked
to exercise that will, who could and did demonstrate to his class every
winter this fact in a remarkable manner. He would say:—‘Gentlemen,
Lord Dundreary asks his brother Sam if he (Sam) can wa-wa-wag his left
ear.” The class would be in a roar to see the old professor’s ears going like
flappers, and his scalp brought almost over his eyes, then drawn quite as
far back as it had been drawn forward, to the unbounded delight of his
audience. Another peculiarity of the scalp is its great vitality. If
the skin of any other part of the body be severed, the chances are ten
to one that it withers and dies. With the scalp, however, thisisnot so. In
accidents people sometimes get scalped as effectually as a Red-skin would
do it for them, such as by the wheel of a cart or carriage running over
the head. Now, an enterprising surgeon, would quickly wash the
scalp free of dirt and place it upon the skull, and with care and
the aid of suitable dressings he would expect it to adhere, and in a
perhaps low percentage of cases, his expectations would certainly be
realized. Other peculiarities, such as baldness, loss of its hair during or
after certain illnesses, &c., will be referred to subsequently.
THe Harr.
The hair of the scalp has also its peculiarities, but we will not stop to
treat of these here, but at once proceed to consider the common characters
of hair, whether on the scalp or elsewhere. A hair, then, consists of :—
1. A Root,
2. A Shaft; and
3. A Point.
The root of the hair is lighter in colour and softer than the stem. It
swells out into a bulbous enlargement or knob, and is received into a
recess of the skin named the hatr-follicle. We will pass over this
at present, as it will be better demonstrated in a subsequent issue of a
vertical section.
The stem, in its transverse section, is well seen in the accompanying
lithograph. The stem is usually cylindrical, especially as it emerges from
its pit, or follicle, but in natural hair, growing to its full length, and not
interfered with by the razor or scissors, the stem becomes gradually
smaller towards the point. The length and thickness vary greatly in
individuals: in the different regions of the body; also in the various
POPULAR MICROSCOPICAL STUDIES. 9
races of mankind. In the straight-haired races, the individual hairs are
coarser and thicker, and the section more circular than in the woolly-
haired races, in which the section is smaller, and oval, the hairs being
sometimes markedly flattened... The section is largesu in the North
American Indians, Chinese, and especially in the » Japanese ; ; light-coloured
hair being usually finer than black. The stem, again, is surrounded re
scales, which lie upon the surface exactly like the slates on the top of :
house ; that is to say, one scale overlaps another. Within this ae
covering is a fibrous substance, which in all cases constitutes the chief
part of, and, often, the whole stem, but in many hairs the axis or centre
is hollow, and occupied by a kind of pith. This is so in our present
section. The outer coat of scales is stained with carmine: the middle
fibrous coat is a very pale blue, whilst the centre cavity can be well seen
to vontain a brownish, granular-looking mass—the pith, or medulla.
The latter, in some cases, fills the cavity, but in others it has shrunk, and
left the sides. The fibrous substance is tr: inslucent, aud may be broken into
long fibres, which, when separate, are found to be flattened. These fibres,
again, may be further found to be made up of flattened fusiform cells.
Very slender elongated nuclei may be seen, also specks containing air,
caused by minute cavities. ..These air spaces are abundant in white
hairs. The medulla or pith does not exist in al] hairs. It is absent in
the fine hairs covering the body. When present, 1t occupies the centre
of the shaft, and ceases towards the point. It is seen to be darker than
the fibrous part when viewed by transmitted light, but by reflected light
it is white, its colour being due to particles of air. It is composed of rows
of soft cells, containing fine granu:es and air.
Viewed with a low power, it will be further observed that the hairs and
their follicles are in groups of threeand four, more rarely two, and very occa-
sionally they are single. Each hair, with its follicle, has accompaniments,
of which the most conspicuous in our present section is the sebaceous
gland. ‘Transverse sections of these glands are very beautiful, here every
cell of the gland and every nucleus within its cell being mapped out by the
delicate staining reagents. As we see these sebaceous glands now, they
appear round or pear shaped, according to the way the gland has heen cut.
_These glands are like pears in shape, the stem of the pear being upper-
most, and the body hanging down, swinging, so to speak, by the side of
the follicle. Therefore, if we look at one cut through the “stem,” we are
really looking into the mouth of the gland, and we find it round and of
small diameter. There are very few in the present instance: the majorily of
the glands are cut across their middle, especially the upper part of the middle
—the depth of the section just allowing the bottom of the gland to be pre-
sent, and this is seen almost without altering the focus of our low power.
Besides these sebaceous glanils we see minute bundles or masses of patie
quite irregular both in shape and size, stained a very pale blue. Se
staff shaped nuclei stained red reveal the nature of these litile bodies
they are parts of the minute muscles of the hair follicles or muscles of
1The artist has chosen a part of the section where these are quite absent
10 THE HAIR AND ITS FOLLICLES, Wc.
the hairs. These will be seen at length in the subsequent vertical
section as slender bundles of plain muscular tissue connected with the
hair follicles, but generally arising by.a number of very small bundles
from the under part of the corium. In other words, every hair has its
little muscle to ‘‘ make it stand on end,” and every little muscle arises |
or takes its origin, or fixed point, in the under surface of the corium ;.
these minute origin bundles then unite : pass obliquely downwards and as
one bundle, take insertion into the outside of the pit or follicle holding
the hair below the sebaceous glands. | Of course, in our present section,
that part of the shift (
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SPONGE.
DESCRIPTION OF PLATE.
1. abande Flagellate sarcoids, a and ¢ with collar, d group of flagel-
late sarcoids seen in plan, e Amoebiform sarcoid,
2. Semidiagrammatic section of horny sponge showing the oscula and
ciliated chambers. The arrows indicate the direction of the
currents.
Section of horny sponge—Chalina oculata with spicules in situ.
Various forms of sponge spicules.
a oe
The soft, tough, porous material which lends its name to this article is
perfectly familiar to everyone, and most persons have a vague idea that
it is a production of the animal or vegetable kingdom, the general im-
pression being that it is due to an insect similar to the creature credited
by popular fancy with the formation of coral. Indeed it is really wonderful
how comprehensive the term “ insect” is in the mind of the non-biologi-
cal public. Just as any physical phenomenon which is not understood
is unhesitatingly ascribed to electricity, so any animal smaller than a
mouse, unless it be a fish, is an insect. But even this idea of the origin
of sponges, vague and erroneous as it is, marks an advance on a previous
state, for it is not so very long since even naturalists of eminence, who
had studied the sponge, were unable to agree as to its animal nature at.
all, many stoutly maintaining for it a vegetable origin. So for fifty
years the sponge remained in purgatory unable to find a permanent place
in either kingdom. Nor can the biologists of the present generation
plume themselves very highly on their comprehension of the nature and
affinities of this animal or colony of animals, which still remains in this
year of grace 1884 as great an ‘“‘ anomaly ” as “the Conservative working
man.”
In taking up the study of this “form of life,” we must be prepared
to descend very low indeed in the scale of life—almost to the very
bottom of the animal kingdom—to those realms where heads, limbs,
bones, muscles, mouths, vessels, nerves, lungs, and organs of sense, or of
anything else for that matter, are left far behind, and the animal or zooid,
if it possesses what may without flattery be called a shape, may be con-
gratulated on its superiority over some of its near relations.
44 POPULAR MICROSCOPICAL STUDIES.
The material known in commerce as sponge is obtained by divers from
the sea-bottom in the neighbourhood of the Greek Archipelago, the Baha-
mas, and other parts of the world, but itis not the whole animal but only
a supporting skeleton from which all the living matter has been removed
by washing, squeezing, and bleaching in the sun. If a piece of this
sponge be examined with the naked eye there will be seen numerous
large, more or less circular openings leading into canals which branch and
penetrate the sponge in all parts and freely communicate with one an-
other. A simple lens of high power will show that the substance of this
skeleton is composed of an open feltwork of curling and branching fibres
of a horny substance called keratode (Gr. keras, horn ; e/dos, form). In
a living sponge this cannot be made out, for the skeleton is then covered
with a slimy material and only the larger openings are then visible.
Sections of the living sponge in any direction would show that this same
slimy substance pervaded the whole interior, covering all the fibres and
lamellz and leaving only a series of narrow, branched canals, the smaller
branches of which communicated with a number of microscopic openings
called ‘ pores” in the outside of this gelatinous mass.
If a healthy sponge be examined in some of its native water, to which
some finely-divided solid substance—say carmine—has been added, it
may be observed that currents of water are constantly flowing into these
pores, while other currents are streaming away from the larger apertures,
called oscula (Lat. dim. of os, mouth). It is thus evident that there is a
constant circulation of water entering the sponge by the pores or znhalent
apertures, traversing the various channels in the substance of the sponge,
and emerging from the oscula or exhalent apertures. Fig. 2, plate 10,
shows, by arrows, the direction of these currents.
Sections of fresh sponge display the fact that the slimy sub-
stance—the so-called sponge jlesh—consists of an assemblage of nu-
cleated corpuscles or sarcotds, about z0'oo or svox Of an inch in diameter,
and of irregular and inconstant form (see Plate 10, fig. 1., ¢) Each
consists of a speck of colourless protoplasm, the semi-fluid granular in-
terior of which—the endosare (Gr. endon, within; sara, flesh) passes
into a firmer clear outer layer—the ectosare (Gr. ektos, outside). In the
endosarc, besides the nucleus there 1s sometimes a little cavity—contrac-
tile vesicle—endowed with the power of rhythmic dilation and contrae-
tion. The sarcoid has the power of changing its form by the protrusion
of blunt processes—from any part of its body, and when free from the
mass it can crawl about by the same means. It bears, in fact, a remark-
ably close resemblance to an Amoeba. In various parts of the canals,
especially near the surface of the sponge, there are found round or oval
chambers, lined with a layer of sarcoids, which present some advance in
structure on the simple ameebiform type. Their form is usually columnar
or oval (Plate 10, fig. 1., b. ¢.), they possess nuclei and contractile vesicles,
and their outer layer frequently assumes the character of a distinct limit-
ing membrane. Each possesses a long flagellum (Lat. for whip) which it is
SPONGE. 45
capable of lashing backwards and forwards. In many forms the limiting
membrane is raised up round the base of the flagellum into a membranous
collar, and the sarcoid very closely resembles certain collared infusoria (Fig.
l.c.) Occasionally very peculiar forms are met with, as in fig. 1.¢, where the
flagellum and collar are borne.at the end of a long neck. We can now
understand that the currents which transverse the sponge are caused by
the co-ordinated lashing in one direction of the flagella in these c7liated
chambers, as they are called. But how is this co-ordination brought
about? We do not know. It is one of the mysteries of protozoic life.
Generally on the outside of the sponge, and less constantly in various
parts of the interior, masses of nucleated protoplasm occur, which present
a variation from the amoebal type in the opposite direction to that taken
by the flagellated sarcoids, which we have seen is one of elaboration and
specialisation. The masses in question present a degradation of structure,
for the sarcoids of which they originally consisted have lost all their
individuality, and fused into a continuous film, or syncytiwm, as Haeckel
calls it, and all that remains to mark their presence is their nuclei, but
the mass still retains its functional activity.
In some very few sponges (Myxospongix) there is no skeleton. In
the others the skeleton is usually strengthened, and, in some cases, en-
tirely formed, by spiculae of carbonate of lime or silica. These spiculae
are of most varied and beautiful forms. Im fig. 4 a few of the most
characteristic of these are represented, but if the reader wishes to see what,
a great variety there is, he must be referred to Bowerbank’s splendid
monograph, published by the Ray Society,in which he will see two or three
hundred distinct forms beautifully figured,and if he has nothing else to keep
him out of mischief, he may occupy himself by learning by heart the two or
three hundred names invented for their designation. Just to incite him
to this study we quote three of these names—Exflected elongo-equiangu-
lated triradiate, Furcated attenuato-patento-ternate, Torqueato-tridentate
inequi-anchorate. We confess with all humility that we have not these
terms at our fingers’ ends. It is evident that these spiculae must tend to
the preservation of the species possessing them, for by rendering them
altogether unsuitable for the purpose of man, they are protected from his
depredations, and they must enjoy an equal immunity from the attacks
of other creatures who would otherwise prey upon them, for a mouthful
of the spicules would by most animals be relished about as much as
would a mouthful of their descriptive terms by the average mortal. In
one order of sponges—the Calcispongie—the skeleton consists entirely
of interlaced spiculae of calcic carbonate. In another order—the Fib-
rospongiz, a fibrous keratode skeleton is always present, and in
most forms siliceous spiculae are abundantly distributed (see
fig. 3), not only through the keratode, but in the sponge flesh,
Halichondria, a section of which is issued with this number, belongs
to this order, and shows well the fasciculi of acicular spicules.
The sponges of commerce are those forms of horny sponges which con-
tain no spicule. In other sponges, such as the beautiful Euplectella, the
spicules are very abundant and very closely united, and the quantity of
46 POPULAR MICROSCOPICAL STUDIES.
keratode is excessively small. Finally, in Clionia there is no trace of
keratode, and the skeleton is entirely siliceous.
‘The reproduction of sponges is effected by a sexual process. Nucleated
cells, exactly resembling the ova of higher animals are formed by certain
of the sarcoids becoming detached, and acquiring a spherical form while
retaining their nuclei and nucleoli, while certuin other sarcoids undergo
changes resulting in the breaking up of their contents into numerous
minute bodies—spermatozoa, provided with long vibratile filaments, by
which they can propel themselves through the water, fertilization is
brought about by the contact of one or more spermatozoa with the ovum,
the interior of which then breaks up into two portions which sub-divide
again and again, until the originally single cell comes to consist of a
hollow oval chamber whose walls are composed of two layers of cells—
an inner—endoderm, and an outer—ectoderm. At this stage the embryo is
free, and swims about by means of cilia with which the ectoderm is
covered. One end of the embryo then turns in and converts it into a
hollow sac, and the gastrula, as it is now called, attaches itself by the
closed end to some object at the sea bottom, and loses the cilia of its
ectoderm, the cells of which unite closely with each other to form the
syncytium. Pores appear here and there in the syncytium, through
which inhalent currents are caused to set in by the cilia of the endo-
derm, and the water is discharged by the opening at the apex, which forms
the single exhalent aperture or osculum. Before this period, however,
spicules have made their appearance in the ectoderm, and young sponge
has acquired a tolerably complete skeleton. Many of the Calcispongice
remain permanently in this condition of a hollow chamber with thin
walls and a single osculum. In the more complex sponges further
development takes place mainly by the growth of the syncytium, whereby
the endodermal cells become separated into small groups, which are
ultimately restricted to the ciliated chambers.
In Spongilla, the only sponge inhabiting fresh water, an asexual
process of reproduction also occurs. Certain of the amoebiform sarcoids
retract their processes, become surrounded except at one point, by a
spiculigerous wall, and after a period of rest are set free in the water and
each reproduces the parent form.
The affinities of the sponges are very imperfectly understood, and they
are among the most difficult animals to assign to their proper place in
any system of classification The resemblance of the sarcoids to Amecebee
and Flagellate Infusors is so close, that from a study of the mature forms
they would be unhesitatingly placed in the lowest sub- -kingdom—the
Protozoa. -But among the Protozoa sexual reproduction is very rare,
and a segmented ovum with the subsequent formation of a multicellular
gastrula is a thing altogether unknown, while this character unites the
sponges with the members of the next higher sub-kingdom—the Coelen-
terata, from which, however, they differ very widely in their subsequent
development.
Popular Macroscopical Studies. Vol L. Late Ll
FG del ad nat TW Watson del et ith
Sti ACR. GH
Sarsaparilla officinalis.
xX 400
Watson & Sor Ube 33 Ct Charles S¢ Barmi™
STARCH.
DESCRIPTION OF PLATB.
———————
Trans. sect. root of sarsaparilla (smilax) officinalis, showing medull-
ary parenchyma with intercellular passages, and starch grains in situ in
cells. Ordinary light, x 400°1-6. Detached grains and granules as seen
under the same magnifying power, but drawn on a larger scale. Crossed
Nicols. 1. Simple grain, showing striation, one zone being more dis-
tinct than the rest. 2. Compound grain of irregular form, showing two
of the component granules, Side view. 3. Compound grain. End view,
showing the three granules. 5, Side view of compound grain of regular
form. 4 and 6. Detached granules.
&
When exposed to sunshine, all green parts of healthy living
plants, and especially the leaves, are the seat of remarkable
chemical activity. The air, with its small but all-sufficient
quantity of carbon dioxide, which has gained access to the
green cells by means of the stomata and the intercellular passages,
and the water forming the chief constituent of the cell sap, being
brought into close relation to each other there result a series of most
important synthetical operations which cannot be brought about by any
other nieans known to chemists Under the influence of the sunshine
and the chlorophyll the carbon dioxide (C O,) is decomposed, its oxygen
is liberated, and the carbon and the water unite with each other directly,
in certain proportions, to form organic compounds of greater or less
complexity, which are used by the plant for the crowth of the young
cells, and the nutrition of all living parts. Among these first products
of assimilation,’ as this process is called, are sugar, oil and fat, and
starch. When assimilation is in excess of the present demands of the
plant, the excess of nutrient matter is removed from the cells in which
it is formed, and stored up in other parts for future use. When the first-
1This term is here used in the perverted sense customary among botanists.
Properly assimilation is the process by which the prepared nutriment is incorporated
with the actual substance of the plant, and becomes part of its body.
48 POPULAR MICROSCOPICAL STUDIES.
formed products are soluble in the cell sap, their transmission is of course
readily explained by the constant circulation of sap, but when insoluble
the transmission must be otherwise accounted for. The substance, in
fact, must undergo a process of metastasis, or conversion into some
soluble body, and this, on its arrival at the place of deposition, may be
reconverted into its original insoluble state, and so remain until it is
required for use.
Of these substances starch is by far the most important. It is one of
a class of bodies called carbo-hydrates, that is, it consists of a compound
of carbon with oxygen and hydrogen in the proportion of 1 part of oxygen
to 2 of hydrogen, or in other words, in the proportion in which they exist -
in water. So we may regard starch as a compound of carbon and water.
This fact should be borne in mind in connection with its use asa dietetic,
for its hydrogen being already completely oxidised or. burnt cannot con-
tribute to the production of heat in the body, and so does not take equal
rank as a heat producer with the fats and oils in which the hydrogen as
well as the carbon is in excess. Starch is insoluble in water and cell
sap. When analysed it yields the proportional constitution C,H,,0,, but
these figures do not represent the true complexity of its molecule, which
is best represented by nC,H,O, in which n is used in the
algebraical sense to stand for an unknown quantity, but probably
= 3, so that the true formula would be C,,HyO,;. It is closely
related to glycogen or liver starch, dextrin and cellulose, and although all
these bodies differ in their physical and many of their chemical pro-
perties, they have exactly the same composition, or, as chemists say—
they are zsomerous. From glucose or grape sugar, the formula of which
is nC, Hy» O, It differs only in the possession of one molecule less of
water, and is easily convertible into that substance. Treated with a very
~ dilute solution of dodine starch assumes a purplish blue colour, and this
reaction being very delicate and highly characteristic of starch, affords
the most valuable test for that substance, even the optical one to be pre-
sently mentioned not excepted. It has been usually assumed that the
iodine formed a definite compound with the starch (the so-called iodide
of starch), but there is reason to believe that it is only deposited on the
starch in a metallic state.
By the action of an organic nitrogenous body of very doubtful compo-
sition, called diastase, produced in germinating seeds, and by other means,
starch is converted into dextrin and glucose, both of which are readily
soluble in water or the cell sap, ‘This, of course, is important in explain-
ing how the insoluble starch may find its way from the chlorophyll
grains, in which it originates, to the cells where it is stored.
Starch is first formed in the interior of the chlorophyll grains as
minute, rounded, solid particles. During the whole time the green
leaves are exposed to sun light, an accumulation of these particles occurs
in the chlorophyll grains, but as soon as the lght fades the quantity
ON STARCH. 49
which has been accumulating all day decreases, and the starch is gradually
removed in the form of dextrin, or some other soluble form, then on
reaching the receptacle in which it is to be stored an inverse change
ensues and the dextrin is once more converted into starch, in which form
it is deposited. Although the process of removal of the original particles
of starch from the chlorophyll ¢ grains can be traced only at night, it, in
all probability, goes on constantly, but during the daytime the rate of
removal is insufficient to counterbalance the larger amount of new
material formed.
In the chlorophyll grains the particles of starch never reach any
higher degree of organisation than that mentioned above, but in the
stems, tubers, roots, ‘thizomes, seeds, and other parts where it is stored
for future use, it assumes the form of complex and definitely-organised
grains, whose form is characteristic of the genus or species in which they
occur. The grains are frequently of a large size, but the size varies. con-
siderably, being in some plants almost immeasureably minute, in others
as the Potato and Tous-les-mois, attaining a diameter of as much as a four-
hundredth of an inch, and being readily visible with a simple lens. In
the same plant, and even the same cell, the size varies considerably, being
dependent chiefly on the relative age of the grains, so that when measures
of starch grains from various sources are given, they must be taken
only to represent an average, and much latitude must be allowed
for individual variation. In some plants, though—the Sarsaparilla
for instance—the variation in size is less marked. The forms of
the starch grains are as variable as their sizes. In the potato
they are oval, in the bean elliptical, in some orchids spherical, in
the wheat grain lenticular, in the maize polyangular, in ginger root,
like short bent rods, and in the laticiferous cells of Euphorbia
peculiar bone-like forms occur. In the oat the grains are compound,
consisting of a number of closely packed, but readily separable, granules.
Examined under a sufficiently high power, and in a suitable medium
(50 per cent. glycerine answers well), a dark spot will be seen in most
grains. This is called the hilum or nucleus and is usually placed eccentri-
cally. In those grains which are elliptical, it is placed nearest the narrow
end of the grain. Surrounding the hilum will be observed a number
of zones, alternately light and dark, due to alternations of more and less
watery layers, and besides these alternations of much and
little water in the layers, there is a progressive increase in the quan-
tity of water or decrease in the density of the layers from without inwards,
the hilum being always the darkest and most watery part. That this is
a correct explanation of the appearance of the layers may be seen by ob-
serving the grains in a medium—alcohol, for instance—which abstracts
the water, and entirely, or almost entirely, obliterates the appearance of
zoning. When the grains are allowed to dry, the striation is also very
indistinct, and the place of the hilum is then usually seen to be occupied
by a cavity containing air. A stratum of air also sometimes occurs be-
50 POPULAR MICROSCOPICAL STUDIES.
tween two layers, and brings them into view when they would otherwise
be invisible. In the dry grains, too, a number of cracks may be seen
radiating from the hilum, and produced by the greater shrinkage of the
central parts of the grain in consequence of the greater loss of water from
them than from the outer layers.
Coneerning the mode of growth of the grain, and the origin of
the layers, there has been, and is, much dispute. One set of observers
state that the growth takes place as in a crystal, by accretion or depost-
tion of layers, alternately more or less hydrated, on the outside
of the grain, so that the outermost layers are the youngest. But
Sachs, following Naegeli, maintains that the grains grow by intussuscep-
tion or deposition of molecules in the interior of the grain between already
existing molecules, and weighty arguments are adduced in favour of this
view.
The excentric position of the hilum is thus explained. The starch is:
never deposited in entirely dead and empty cells, but usually in cells
whose vital activity is reduced, and but a lining zone of protoplasm
remains. It is in this layer that the growth of the grain
commences, and as it increases in size it is pushed towards the
centre of the cell and is no longer entirely surrounded by protoplasm,
and the part so removed from contact with the protoplasm naturally
grows more slowly than the side that is still imbedded. Sometimes the
starch is deposited in hollow vescicles in the protoplasm, then as growth
takes place the grain extends into the cavity away from the protoplasm,
and the same irregular growth as before results.
The hilum commonly conforms to the shape of the grain. In elliptical
grains it is elongated in direction of the longest axis of the ellipse,
and in lenticular grains the hilum is lenticular. Occasionally, two or more
nucleiappear in one grain, and concentric layers are deposited around each,
Thisisoftenseenintheharicot bean. When it occurs the most rapid growth
usually takes place in the line joining the two nuclei, and a rupture at length
takes place, whereby the original single grain becomes divided into two,
though they may still remain in contact with each other, Such compound
grains occur in Sarsaparilla. Examined under a quarter or eighth inch
object glass. The cells of the cortex and medulla will be seen to be
filled with rounded grains, most of which show traces of a division into
three separate granules. In this balsam preparation it is not easy to see
the striation for the reason above given, but some grains are sure to shew
ib under a suitable illumination. It will then be seen that the layers do
not encircle the grain as a whole, but each granule has its own hilum
surrounded by its own concentric layers. Very often one or two divisions.
are much more pronounced than the rest, as shewn in fig. 1 plate 11.
Starch assumes a most characteristic appearance under polarised light.
Space will not allow, nor is it needful to enter into an account of the
+e
ON STARCH. 51.
nature: of Paeaead light, ete which we. must assume our readers to be
in soyse degree familiar,:~. It will suffice here*to draw attention to the .
phefidmena presented by ie use. When starch is examined under crossed
nigols thie field remains.dark, but each granule assumes a glistening grey
appearance, as_ if self- luminous, and is marked. with a black cross. ity
then, the object be slowly rapntad in the field of view, it will be seen
that the cross remains fixed with regard to the field, one pair of its arms
being parallel to the principal plane of the polariser and the other parallel
to the principal plane of the analyser. As the arms of the cross, however,
are frequently curved, their direction does not always appear to coincide
with these planes. During the rotation, in fact, the grain appears to be.
turned round underneath the stationary cross.
If, the object remaining stationary, the polariser or the analyser. be.
rotated, the cross will be seen to rotate with it but with only half its an-
gular velocity, so that to make a complete rotation of the cross the
analyser or polariser must be rotated twice. If now a thin film of selenite
be interposed between the polariser and the object while the nicols are
crossed, and be rotated until it gives the brightest field, most beautiful
chromatic effects will be obtained. The field will assume a colour depen-
dent upon the thickness of the selenite film, and the interference crosses
will be vividly coloured, the rest of the grains assuming a complementary
colour. Jor instance if a yellow-blue selenite be employed and be so
_ adjusted in the first instance as to give a blue: field the crosses will
be red at the edges merging into yellow in the centre, and the inter-
spaces will be bright green. Then on rotating the analyser or polariser,
as the blue field gradually merges into the complementary yellow, so
the crosses rotate and change to their complementary cclours. By means
of the interference phenomena under polarised light, the compound
nature of the grains in sarsaparilla is most clearly shewn, for each granule
exhibits its own cross and its own chromatic effects. In studying this
preparation, the medulla or pith is the most favourable part, for here the
cells are largest and the starch less closely packed. Some grains will
be met that are not compound and exhibit but a single cross, as
shown in fig. 1. Others will be presented under different aspects,
some showing the triradiate division of the granules as seen in plan .
(see fig. 3). Others a single diametral suture when the grain is seen
from the side as in fig. 5. Frequently the normal spherical form is
departed from (fig. 2). Round the edges of the cells especially, the
grains have, by mutual pressure, assumed the form of very short trun-
cated cones with rounded angles. This is represented in the central
figure. If the observer searches the cells carefully he will probably be
rewarded by finding a few isolated granules, the appearance of which
will of course vary according to their presentment, and these will afford
a better idea of the true form of the granules than could possibly be
obtained by any other means. Occasionally grains are met with having
more than three component granules.
52 POPULAR MIOROSCOPICAL STUDIES.
The South American genus Smilax, from the roots of several species of
which the sarsaparilla of the Pharmacopeia is obtained, belongs to the nat-
ural order Smilacex, which together with a few other orders, presents a re-
markable departure from the normal type of monocotyledons. The form of
the embryo and of the flower, the minute structure of the rial stem and
its branches, and the general character of the plant are exactly those of
other monocotyledons, but the veins in the leaves form a network and
the rhizome or creeping underground stem has its woody tissue disposed
in a ring round a central pith or medulla, and is surrounded in turn by a
parenchymatous cortical layer. These characters are as distinctly
dicotyledonous as those before mentioned are monocotyledonous.! The
arrangement of the bast and xylem in the root is somewhat
different, for instead of each bundle consisting of an internal
woody portion separated by a cambium ring from an external bast portion
the two constituents are arranged collaterally, large xylem bundles con-
sisting of large vessels and thick-walled prosenchymatous cells alterna-
ting with much smaller bast bundles composed in the main of sieve tubes,
the whole being surrounded by a single layer of very thick walled cells, ©
representing the vascular bundle sheath. Under a 1 inch objective this -
arrangement will be well seen in the accompanying preparation, and a
+ inch applied to the sieve tubes will show here and there the perforated
end walls or sieve plates between the ends of adjacent vessels. All the
elements of the root are highly lignified, and polarise strongly witnout
the aid of a selenite.
Cag aa rece ee ee UE eS SE A eee eS
1Contrast this with the trans. sect. of the Bulrush, which is an ordinary
monocotyledon.
ae oF
<*
ca
Popular Mucroscopucal, Studies Voll. Llate Le,
E[D 2 adnate | JW Watson del et ith.
T.S. OF DODDER (CUSCUTA)
yn its host, double stamed_
Ae
Watson & Son. Ath 93, Ct Charles S¢ Burm™
THE DODDER PLANT.
The Dodder plant is a long and iiender stemmed leafless parasite,
rather plentifully distributed throughout most of the counties of England,
but totally unknown as a native in either Scotland or Ireland. It
selects as a host either a shrubby plant, as in the case of the individual
from which the accompanying section was prepared, or, as is more com-
mon, it fixes itself upon certain wild or cultivated plants, such as thy me,
nettles, clover, or flax. It blooms in the summer, the flowers being in
the form of small white or pinkish bells, growing in close unstalked ‘elo-
bular clusters, and passing later into roundish capsules, each containing
four small, brown, and minutely granular seeds. The plant attaches
itself by twining its pale or reddish thread-like stem around the body of
its selected prey, and by sending out, at intervals, along the encroaching
filament, peculiar adventitious roots, suckers, or haustoria, which find
their way into the sap-containing tissues of the host-plant, and not only
function as holdfasts, but, at the same time, also act as ready absorbents
of the nutritive juices, that, during the growing season, are ever circula-
ting within the body of a living plant.
The Dodder, which supplies the subject of our present study, has se-
lected as its host a plant of common heath, but several other plants—in
addition to the few e well known as affording it a
suitable habitat. Furze, broom, i aaa and rockrose are the best
known examples of shrubs; bastard toadflax, camomile, sowthistle,
yellow rattle, and bracken fern as wild herbaceous plants ; while cabbages,
hops, and lucerne may be added as further examples of the cultivated
plants that are subject to the attacks of this agricultural pest.
Dodder belongs to the genus cuscuta of botanists, a word said to be
derived from chessuth or chasuth, the Arabic name for this plant. There
are about 80 different kinds or species of cuscuta distributed throughout
the warm and temperate regions of the earth, and of these four may
be found in England.. The largest and rarest grows upon vetches,
nettles, tansy, &c., and is distributed generally throughout temperate
and sub-tropical Europe, and is known as uropea. Another
form as large possibly as Huropea, but not so red, grows upon
flax. It is not a true native, having been introduced in imported
linseed, and may be found in flax fields in any part of the British Isles,
It is named Zpilinum, from Hpi, signifying that it grows upon, and
linwm, the Latin name for the flax plant. The third form or species of
Cuscuta affects thyme ; it possesses a very slender stem, and has a
European distribution from Denmark southward, extending into North
Africa and Western Asia. It has been named ELpithymum from Epi and
‘thymum, the Latin name for the herb thyme. The species of our pre-
paration is Cuscuta Epithymum, and it not only grows upon thyme and
heath, but upon ling, furze, and other plants, woody and_ herbaceous.
The fourth form of Dodder. found in England may be regarded as a mere
variety of the last. It occurs in clover fields, and is a most troublesome
weed to the agriculturist, It is known as Cuscuta trifolii ; trifolium
(three-leafed) being the generic name for clover.
Cuscuta is known in different parts of the country, by names con-
siderably more expressive of the parasite’s look and behaviour, than the
54 POPULAR MICROSCOPICAL STUDIES.
polite and gentle one of “dodder,” which simply means a tangled thread.
Strangle-weed, hell-weed, and Devil’s-guts are common names given to it
in agricultural districts.
From the structure of the flowers, or reproductive organs of the plant,
a natural relationship with ordinary field or garden convolvulus (bind-
weed) can be clearly traced ; as in these structures, which were devel-
oped at a comparatively late period in the life of the individual, and
structures, too, that are in no way related (other than a relation of de-
pendence) to the purely vegetative functions of the plant, they
have not suffered that degeneration of structure that has be-
fallen the nutritive organs, in consequence of the plant having
taken to the ever-degrading habit of parasitism. As the plant
became more and more better fitted to lead a parasitical life,
organs that were absolutely essential for the performance of the every-day
physiological work of ordinary plant life became useless, then rudimentary
and at last completely lost; thus the leaves not having occasion to.
elaborate food are reduced to the merest rudiments—tiny scales upon
the blanched or red-stained stem; while the true roots have altogether
disappeared—the plant at no time in its existence having been rooted to
the earth. The flowers have five united petals and five stamens inserted,
as in convolvulus, at the base of the corolla bell and alternate with its
lobes. The ovary is superior, or placed in the receptacle above the inser-
tion of the corolla, and consists of two cells or cavities each containing
two ovules—further pointsof floral structure that clearly indicate anaffinity
with the bindweed. The genera Convolvulus and Cuscuta are the only
British representatives of the family ConvotvuLacnu™® of botanists.
When the seeds of Dodder are fully ripe they each contain a slender-
embryo coiled around a central mass of reserve food, or endosperm. The
two cotyledons, so characteristic of the class (DicotyLEpoNns) to which
the family Convolvulacez belongs, are, however, not distinguishable in
this plant. The embryo consists simply of a thread, stouter at one end
than the other, the thicker extremity representing the primitive root or
radicle. When, in the course of time, the seed germinates, the slender-
or plumule end of the embryo bursts the testa and rapidly lengthens,
fed by the nourishment stored away in the seed, and absorbed by the
fleshy radicle. The tip of the sensitive plumule moves round and round,
performing circular journeys in search of a suitable host ; having found
one, say a young clover, flax, or other plant, it twines around it, and is
eventually carried upwards, seed and all, completely off the ground, by
the rapidly elongating host. By the time the store of endosperm matter is-
exhausted, the infant parasite has pierced the thin skinned body of its
prey, and henceforth the suckers provide it with already elaborated
food, equal in value to that which was stored away within the old, but
now cast away seed-coats by the parent dodder plant.
How these suckers act will be best explained and easier understood
after a careful examination is made of the histological relationships exist-
ing between the tissues of the host and its parasite, as exposed in the
accompanying preparation. It will be well to examine first the structure—
of the stem of Heath.
THE DODDER PLANT. 55.
— =
In the centre, as displayed by the transverse section, isthe region of pith,
the cells of whicharerelatively large and many-sided. Examined in a fresh
state and in sections not too thinly cut, the walls may be seen to be
closely pitted with small roundish pits or depressions left in the slightly
thickened side walls. These cells are utilised by the heath plant for the
storage of food, and starch grains may be often observed lying within them.
Surrounding the pith is the region of wood, or as itis sometimes called
the xylem, made up of narrow thickened fibres closely intermixed with
long wide tubes or wood vessels. It is up this fibro-vascular cylinder
that the water, charged with the essential earth salts, passes conducted
especially along the woody fibres, while the long pipes or vessels serve
as channels for the interchange of gases, rendered necessary by the
chemical changes induced by vital energy at the growing or working
regions of the plant. . Lying around the woody fibro-vascular
cylinder is the cortical layer or region of bast, a_ tissue
also composed of fibres and vessels. But the elements of the bast
fibro-vascular cylinder differ not only in structure from those of the wood,
but in certain chemical and physical particulars as well. The function,
moreover, of the two regions is essentially different. The vessels of the
bast, instead of being mete passive conductors of gases, are tubes
containing living protoplasm, and are active distributors of sap relatively
rich in albuminoids.
Outside of all is the protecting layer of corky cells, covered externally
with an epidermis, from which spring numbers of comparatively long,
roughish-looking hairs.
Respecting the structure of the Dodder, it is extremely simple. As
displayed in longitudinal section, it will be observed to consist of a
vascular system, the elements of which are barred with transverse
thickenings, and the whole surrounded by a large-celled parenchymatous
tissue, abundantly filled with grains of starch. There does not appear
to be a very distinct epidermis. The suckers are apparently of the same
general structure as the stem, and, in the preparation, are seen in position
as being thrust through the superficial protecting layer of the host, and
embedded either in the tissue of the bast, or pushed inward through the
wood as far even, in some cases, as the pith.
Remembering that the function of chlorophyll in the vegetable
economy is in connection with the manufacture of starch, it is not
strange that in the Dodder this important green substance should. be
entirely absent, seeing that it can collect starch or its chemical and
physiological equivalent from the passing juices of its host. In all
likelihood the protoplasm contained in the superficial cells of the haustoria
exercise an influence similar to that of the scutellum in the germinating
wheat, enabling the insinuating suckers to not only absorb already
soluble materials or substances dissolved in the sap, but solid
‘material. like grains of starch and protein bodies in addition.
Furthermore, it is by this power, one might conjecture, that
the haustcria can gain an entrance, and push their way into the
stem of the host. When it is remembered how the embryo of the date
for example, can soften and absorb during the period of germination the
56 POPULAR MICROSCOPICAL STUDIES.
exceedingly hard and dense endosperm substance of its seed, one cannot
wonder at the power possessed by the suckers of the Dodder to enter by
the exercise of a similiar digestive power, even the hard woody cylinder
of shrubby plants hke Heath. At all events, it is hardly likely that the
suckers, even although they are provided with a twig from the fibro-
vascular system, “pierce the stem [of the host] like a small thorn,” or again
that the “suckers could not penetrate the clover stem were it not for the
woody skeleton belonging to each sucker,” as is described in a: recently
‘ published text book. |
Parasitism although common among Fungi is comparatively rare in the
rank and file of Flowering Plants. In the class of Dicotyledons there
are no parasites among the forms with free petals, but in the Monopetala,
or those whose flowers have united petals, and in the Apetala@, or those
where there are no petals at all, there are several families possessing
parasitical individuals. Confining ourselves, however, ‘to members of the
British flora, we have the following list :— .
MonopetaL®.—Dodder (Cuscuta) of the order Convolvulaces
Bird’s-nest (IZypopithys or Monotropa) of the order Monotropece found in
woods upon roots of beech and fir.
Bartsia, Eyebright'(Euphrasia ), Yellow-rattle (Rhinanthus ), Lousewort
( Pedicularis ), Cowwheat (Melampyrum), and Toothwort (Lathrea), all
of the order Scrophulariacex, and all parasitical upon roots.
Broom-rape (Orobanche) of the order Orobanchee, parasitic upon roots.
AprtaLa.—Bastard Toad-Flax (Thestum) of the order Santalacee, a
perennial and parasitic upon roots.
Mistletoe (Viscum) of the order LoranTuacea, parasitic on various
trees.
In the class of MonocotyLEpoNs we have Coral-root (Corallorhiza )
and Birds’-nest Orchis ( Neottia) root-parasites of the order Orchidaces,
Epipogum of the same order is a saprophyte, that is, it feeds upon organic
matter derived from lifeless things. It lives amongst decayed leaves and
is exceedingly rare.
In this list two or three plants are given that can only be regarded as
partial parasites. Mistletoe, for example, although it feeds upon the
juices of apple and other trees, its leaves nevertheless contain chlorophyll,
and, within certain limits, manufacture starch from carbon di-oxide and
water just as other green plants do. Its usual mode of procedure there-
fore is to add to the nutritive store enriched by legitimate labour, that
surreptitiously obtained by sucking the food-bearing sap of its woody
host. Rhinanthus and Thesium differing from Mistletoe in being only
parasitical upon roots, the former affecting damp and the latter dry and
chalky pastures, and the other British examples of parasites that still re-
tain the power of developing chlorophyll in their leaf cells.
The most remarkable parasite, and, indeed, the most remarkable plant
perhaps in the whole world, is the Rafflesia Arnoldi of Sumatra, an indi-
vidual consisting entirely of a huge flower of fungoid consistency, pro-
vided with a single sucker which attaches the plant to roots of certain
species of Cissus, trees belonging to the same natural family as the vine.
The flower of this leafless and stemless parasite’ actually measures three
feet in diameter, and weighs upwards of fourteen pounds.
AP RES INIDS Xs,
SECTION Ill.
POPULAR MICROSCOPICAL STUDIES.
PAGE 24,—Il. 9 and 1&, from top; for ‘‘albuminoids” read ‘‘ albumenoids,”’
PaGcE 27.—I. 7 from foot ; for ‘‘ stomate ” read ‘‘ stomata.”
Pace 42.—]. 5 from foot ; for ‘‘ madibles” read ‘‘ mandibles,”
PaGE 45.—]. 21 from top; for ‘‘ spicule” read ‘‘spicula,” and the same error is
repeated several times in this page.
PAGE 46.—l, 23 from foot; for ‘‘and young sponge, &c.,” read ‘‘and the young
sponge, &c.”
PaGE 50.—1]. 10 from foot ; ‘‘ dele” full stop after object-glass, and capital T from
next word. The sentence should read ‘‘ Examined under a quarter or eighth-
inch object-glass the cells of the cortex, &c..”
INDEX.
SECTION III.
POPULAR MICROSCOPICAL STUDIES.
A,
Aerial branch of Bulrush, 29.
Alimentary Canal, 33.
Anatomy of Tipula, 40.
Antenne of Tipula, 41,
Anther cells, 15.
B.
BIBLIOGRAPHY—Glands, 14.
Hair, 14.
Lymphatics, 14.
Ovary of Poppy, 20,
Bulrush (The), 29.
i Flowers of, 30.
.. Meristem of, 29.
C
Cellulose, 24,
Ciliated Chambers of Sponge, 45.
Chlorophyll, 49, 55.
Convolvulus, 54,
Crane Fly (The), 39.
Cuscuta, 53.
D
Diastase, 48.
Dodder Plant (The), 53.
rs Flowers of, 54.
‘e Suckers of, 54.
as Structure of, 55,
E
Embryo Sac, 15.
Embryo of Wheat, 23.
Endosperm, 21, 23.
Eyes of Tipula, 40.
F
Fertilisation of Poppy, 18.
Flannan Islands, 1.
Flowers of Bulrush, 30.
Dodder Plant, 54.
” 29
G
Glands (sebaceous), 9.
Gneiss (Hebridian), 1,
Grain of Wheat (A), 21.
Composition of, 24.
Protoplasm of, 25.
Starch of, 28.
H
9? 9
99 9?
i) 9?
Hair (The), 8.
5» follicles, 9, 10,11, (muscles of) 12.
;, medulla of, 12.
Halichondria, 45.
Head of Tipula, 40.
Hebridian Gneiss, 1.
Hilum of Starch grains, 49.
How to prepare Rock Sections, 4.
Human Scalp (The), 7.
I
Tleum of Cat, 33; (villi of) 35.
Internal organs of Tipula, 40.
Intestine (‘The), 33.
K
Keratode of Sponge, 44.
M
METHODS OF PREPARATION :-—
Human scalp, 14.
Ovary of poppy, 19.
Rock sections, 4
Micropyle, 17.
Mistletoe, 56.
Mouth of Tipula, 41.
Muscles of Hair Follicles, 12.
Myxo Spongiae, 45.
O
Occipito Frontalis (Muscle), 7.
Oscula of Sponge, 44
Ovary of Poppy, 15 (fertilisation of),
18
Ovule, 15.
P Spongilla, 46.
Starch, 47 (Hilum of), 49.
Stigmas, 16.
Stomach (The) 37.
Structure of the Dodder Plant, 55,
Panniculus Carnosus (Muscle), 7.
Parasitism of Plants, 66.
Pericarp, 22, 23.
Plumule, 22.
Pollen grains, 15.
Poppy (Ovary of), 15. fb
Testa, 23.
R Tipula 39 (Anatomy of) 39.
Radicle, 22. », Antenne of, 41.
Rafflesia Arnoldi, 56. ,, Heyes of, 40.
Rock Sections (How to prepare), 4. », Head of, 40.
Ss ,, Internal organs of, 40.
. », Larve of, 39.
Sarcoids of Sponge, 44. Mouth of. 41.
Sarsaparilla officinalis, 47, 52. 42 Trophi of a
Scalp (the human), 7. is ee
Scutellum, 22
Sebaceous Glands, 9. V
Sponge, 43. Vessels of Intestine, 36.
,, Ciliated Chambers of, 45. Villi of . an
.» Keratode of, 44.
.» Oscula of, 44. W
Sarcoids of, 44. :
Spermatozoa of, 46. Wheat (A Grain of) 21,
THE METHODS OF MICROSCOPIGAL
RESEARCH, |
AN INTRODUCTORY ESSAY
TO STUDIES IN
MICROSCOPICAL SCLENCE,
EDITED BY
ARTHUR C. COLE, F.R.M:S.
CONTENTS.
PAGE
Part I. Introductory i,
II. The Microscope ~ v.
IIL. The Human Eye “ati
Iv. & V. The Preparation of Tissues XVii.
VI. Section Cutting XXxiii.
VII. On Staining xli.
VIII.to XI. On Mounting xlv,
XII. On Microscopical Art Ixiii.
XIII. On Microphotography Ixxiii.
THE METHODS K % _
i Qe.
MICROSCOPICAL RESEARCH.
INTRODUCTION.
I.—Own INSTRUMENTS AND THEIR USEs.
The investigation of minute structure, whether organic or inorganic
can only be accomplished through the use of adequate optical instru
ments. The organ of visionin man is so constructed that the distance
of most distinct vision wavers between eight and ten inches from the
normal eye of an adult. This is due to the alterable curvature of the
erystalline lens which permits of the practically parallel pencil of
rays from a distant object or the divergent rays, from one close
to the eye, to be accurately focussed on the retina or sensitive part
of that organ; but if the object be brought still closer to the
eye than the normal distance of most distinct vision, it gradually
loses its power of accommodation in exerting the necessary strain which
is required to render the crystalline lens convex enough to focalise the
image of the object upon the retina ; about two inches from the eye this
strain becomes impossible. Within the limits of accommodation only
megascopical characters can be appreciated. Were the eye capable
of altering the curvature of its crystalline lens indefinitely, its
power of vision would become illimitable; telescopes and microscopes
would then be found unnecessary But the bounds of natural
limitation can be conquered by artificial means, and the interposition
of a sufficiently convex lens between the near object and the eye,
alters the direction of the rays of light which proceed from the object, so
as to bring them within the scope of natural vision ; and herein lies the
theory on which the microscope has been eeyra nied: The nearer an
object is brought to the eye, the greater does its visual angle (or angle
produced by the intersection of rays or straight lines from the extreme
points of the object) become, and, consequen tly, a larger image is focussed
on the retina.
Optical instruments then are required at the outset to enable one to
enter the domains of histology; they may be directly employ ed, in a
multitude of instances, where the objects are of minute size. Equally
vast in number, however, are the substances which cannot be directly
examined, but require special processes to render them suitable for mi-
ll. THE METHODS OF MICROSCOPICGAL RESEARCH.
croscopical examination. In the inorganic kingdom minerals, rocks
and chemical substances, elementary or otherwise, are found in
nature in such minute particles as to render them _ suitable
for immediate study under the microscope; but, in the ma-
jority of instances, they require to be pulverised, sliced, or
precipitated ere they come within the range of observation, and to
these ends the petrologist must be provided with chisels and hammers,
slicing and grinding apparatus, and a variety of other tools adapted to the
collection and subsequent treatment of specimens, whilst the chemist
must stock himself with blowpipes, test tubes and matrasses, reagents,
and balances, In the organic world the vegetable histologist will require
a spud and vasculum, dipping bottles, collecting apparatus of all kinds,
and a variety of instruments to facilitate the examinationof the unicellular
and delicate forms, whilst the more complex examples will require to be
dissected before they can be utilised. The animal histologist will find
his work inextricably linked with that of his brother botanist, and to a
large extent will work hand in hand with him; but in the progression of
his inquiries there will arise a necessity for other instruments, such as
bone-forceps, saws, and knives of divers shapes.
The study of both organic and inorganic histology is so complicated,
that words alone are often inadequate toits wants. Diagrams and draw-
ings are therefore employed to supplement what language often fails to ex-
press. There has thus arisen the necessity for instrumental aid in this
direction, and it becomes the duty of the investigator to learn their con-
struction and use.
IJ.—On REAGENTS, THEIR CONSTITUTION AND ACTION.
One of the most important items in the study of microscopical tech-
nology, is concerned with the action of reagents. It often happens that
the optical means at the disposal of the histologist are insufficient to
the resolution of structure, and although much may be done with
carefully-directed and modified light, still, the utility of the judicious
application of reagents requires only to be understood to be appre-
ciated.
The knowledge of the chemical constitution, physical properties, and
modes of manufacture of reagents, often leads to the discovery of their
specific action on minute structure, whether those consist in a revelation
of inherent qualities, or in a modification of details. It thus becomes
incumbent that the histologist should carefully scrutinise all kinds of
reagents, and record the results of such examination.
Reagents may be used in a variety of ways, for the elucidation of
structure and the detection of the constitution of bodies. Some are
employed as chemical tests, others as stains or to induce changes whereby —
certain properties are revealed, whilst another set are exhibited as _pre-
servative media. To know exactly what to apply, and how to apply it
for the revelation of specific phenomena, is the essence of this department
of microscopical manipulation.
INTRODUCTION. ill.
IIJ.—On tor Metruops oF PREPARATION.
Both organic and inorganic matters require special methods for their
preparation as a means of study. Thus, the processes of pulverisation,
levigation, of shtting, and of grinding minerals and rocks, are beset with
difficulties of detail, which, for want of suitable attention, prove to be
insurmountable barriers to the tyro, whereas their observance but shows
that he has made a ‘‘ mountain of a mole-hill.” So, also, the impediments
to successful section-cutting, staining, and mounting are all traceable to
a neglect of minute particulars, such as the wetting of the edge of the
razor with spirit, the practice of drying the edge of the blade when it is
set down for a few minutes, the use of a mordant previous to staining
certain vegetable tissues, or the thorough dehydration of sections before
they are mounted in Canada balsam or dammar solution.
In the opening pages of his work on the microscope,! Beate makes
the following observations :—‘‘ Manual dexterity, although subordinate
to many higher mental qualifications, is as essential for the successful
prosecution of microscopic observation as it is for that of every kind of
experimental science. It assistsusin the discovery of new means of enquiry
and in devising methods by which difficulties may besurmounted. Without
skilful manipulation we can neither teach by demonstration facts which
have been already discovered, nor hope to extend the limits of observa-
tion and experimental knowledge. It is not, therefore, surprising that
many of the most important facts which have been recently added to
microscopical science, have been discovered by men who had _ previously
well-trained themselves in experiment-—particularly in practical chem-
istry and minute anatomical dissection. Improvements in the practical
details of manipulation almost necessarily precede an advance in natural
knowledge, and invariably promote and expedite true scientific pro-
gress.”
But although manipulative skill is a very necessary adjunct to micros-
copical research, an attainment of the understanding of the general prin-
ciples of action at the outset, sometimes proves to be the most arduous
portion of the work, and very often is the only impediment to success.
Practice and perseverance, brought to bear upon previously gained know
ledge, are the only royal roads to manual dexterity, and it thus becomes
the duty of the instructor to point out, not merely what path ought to be
taken, but the various pit-falls which everywhere surround the beaten
track, and how best to avoid them.
ITV.—On MicroscopicaL ART.
There are two ways in which microscopical objects can be drawn so as
to become useful records of research. By the first of these, a rough dia-
grammatic representation may be made, without reference to accuracy of
1How to Work with the Microscope, 5th Ed., London, 1880, p. 1.
Vi. THE METHODS OF MICROSCOPICAL RESEARCH.
form or size; merely to display the author’s views concerning the structure
of the object. The second method is to make an accurate drawing with
due ward to the size and shape of the object under the microscope.
30th of these methods are valuable in themselves, but their usefulness
becomes immeasurably enhanced when they are combined so as to afford
scope to the artistic skill and scientific knowledge of the draughtsman.
There is a great deal of truth in the statement that true ait is the out-
come of genius, bue that does not in any way affect microscopical drawing;
it will be found that patience and practice are sufficient to enable the
student to overcome every obstacle, aud to achieve the most satisfactory
results in this department of art. Photography, and lithographic draw-
ing, also, need only to be attempted, to convince the worker that perse-
verance, here as elsewhere, is the only serious impediment to success.
In the ensuing chapters every general statement will be followed by
some special example, and the study of types thus afforded, will endow
the beginner with material for extended microscopical research.
ON INSTRUMENTS AND THEIR USES.
CHAPTER I.
THE MICROSCOPE.
The microscope, as an instrument of power in histological research,
depends essentially in construction, upon its conformity with the laws of
light and human vision. It has already been stated that an idea of the
size of an object is arrived at through the size of the image focussed upon
the retina, and that these dimensions vary in proportion as the object is
brought near to, or removed farther from, the eye. When the object is
brought close to the eye, its visual angle,—that is the angle formed by
the crossing of the rays from the extreme points of the object, is larger
than when it is placed farther off, and, consequently, the image on the
retina is larger also. If this principle were capable of unlimited exten-
sion, it would obviously follow, that to keep on magnifying an object,
all one would have to do would be to bring the object closer
and closer to the eye. But there isa hmit to this natural power of
microscopical vision in the human subject, and the eye fails signally
to accomplish its office when the object is brought within
about two inches from its surface. The reason of this is, that, the
crystalline lens of the eye, in assuming a more convex shape
through the relaxation of the ciliary muscle, becomes overtaxed at this
distance. If, now, a sufficiently convex lens be placed between the ob-
ject and the eye, so as to enable the divergent rays to be accurately focussed
upon the retina, the difficulty will be overcome, and, theoretically, micro-
scopical visicn would be illimitable. But, is it so? Most certainly not
The employment of artificial substances, such as crown and flint glass,
diamonds, ete., although they considerably extend the power of sight,
do not do so ad infinitum. Here the limitation is purely material, as
distinguished from the former instance, the human eye, which is defec-
tive not only materially, but physiologically.
Vi. THE MICROSCOPE.
The worker in the field of microscopical research, need not, however,
be appalled by these statements ; for, it will be found that the human
organ of vision, In conjunction with the excellent apphances of modern
invention, will enable him to approach, and sometimes even to solve satis-
factorily, many of those philosophical problems which underlie the evo-
lution of things, both animate and inanimate. In exemplification of this,
a few instances may here be recorded.
The practical geologist who sallies forth into the field with lens in
hand, may gather during his walk a variety of rocks, which, from their
cosmological structure, point to an igneous origin; some of the specimens
re coarse grained, whilst others defy the utmost scrutiny of the eye.
The microscope is brought to bear upon the question, and he finds that a
power of 500 diameters is generally the utmost degree of amplification he
will require to employ; but for all practical purposes powers of from 20
to 100 diameters suffice. With the assistance of the microscope he is
enabled to pronounce with decision that the rovks are igneous; and
more, from analytical and synthetical experiments he can show that cer-
tain coarse varieties, which are thoroughly crystalline (the crystals being
simply held together by adhesive and cohesive forces, without the neces-
sity of an interstitial binding substance), are of deep seated origin, and
consolidated under conditions of enormous pressure and a length of time.
He is, in like manner, able to affirm of the other varieties, what their
mineral constituents are, or have been, and how they came to assume their
present states. Thus he builds a part of the fabric of geological philosophy,
and with what ?—with a comparatively low power of the microscope.
To take an example from the organic world ; the questions of the func-
tion of various parts of the body, are very often arrived at through a
minute study of its members. The form and general appearance of the
cells of glands such as the salivary glands, point to the functions they
perform, whether they secrete or absorb, and how and when they perform
their duties. The study of amceboid, and even of ciliary motion, under
the microscope, does not require a power of magnification, much beyond
700 diameters, whilst the life-history of the minute forms of life known
as germs (Bacteria, etc.), may be readily comprehended, by the use of
from 700-1200 diameters. It is only when such things as the delicate
markings on the skeletons of Diatoms, or the artificial ruled lines on
glass (Nobert’s test) require to be made out, that powers beyond 1,200
diameters become useful ; and it must be admitted that the scientific in-
vestigator does not lose anything, nor are any of his philosophical deduc-
tions vitiated by eschewing such powerful instruments, which, in the
hands of the skilful, succeed in amplifying and resolving certain pretty
structures ; but, to the ordinary worker are, in reality, impediments to
research.
On the threshold of this inquiry, it thus becomes evident, that an ac-
quaintance with the general structure of the human eye, coupled with the
principles of luminous energ gy, are necessary adjuncts to an understanding
of the microscope its place, and power.
Mc. Research. Platel..
Addl ad nat.
Watson x Son, Chromotithog™s Newhall St, Birn.
THE HUMAN EYE.
Slightly altere | (by permission) from: a paper read before the. Man-
chester Microscopical Society, by Georas E. Davis, F.R.M.S., F.1LC.,
F.C.8., &e.
DESCRIPTION oF Puate I.
a, Anterior chamber of eye fitted with the aqueous humour. c,
Cornea. 7, iris. p, pupil.
cm, Ciliary muscle. cp, ciliary processes. /, lens.
s, Sclerotic Coat. c, Choroid. 7, retina.
Jf, Forea. RR, Superior and inferior recti muscles.
O, Optic nerve entering the sclerotic and choroid coats.
In all studies, whether of pure Microscopy as a Science, or whether of
one of those departments of Natural History in which the microscope is
employed as an aid to vision, we must, at the outset, recognise the im-
portance of a study of the human eye.
It may be the seat of many imperfections resulting from misuse, old
age, or disease, which are apt to modify the conclusions we may draw
from our observations, unless we are careful to study well into what lines
such imperfections may lead us,
Nature has given us in this organ a means whereby all objects may be
compared with each other, more especially as to size, colour, and general
characters, and it must astonish the student, who thinks deeply, to find
that so little is known definitely as to how we are able to appreciate
magnitudes, colours, and forms. It is easy to say that the eye lenses
focus a picture of the object upon the retina, and the irritations are car-
ried by the optic nerve to the brain, but do we practically realize what
this means ?
Then again, unless more of our senses than one are brought to bear
upon a matter under consideration, we can scarcely form a true opinion
upon our subject.
Take something which greets our vision for the first time. We
know not what it is; we can see it, it is true, but we have to bring
in the aid of other senses before we can arrive at a correct judgment ;
and even then, our judgment being the result of comparison, and also of
experimental contact of substances with our senses—so to speak—opinions
Vili. METHODS OF MICGROSGOPICAL RESEARCH.
which are formed must, to a certain extent, be modified by the amount of
other experience to which our nerve centres have been previously sub-
jected.
Take two experts ; vive to each one asphere composed of lead and tin.
Upon asking them what substance they were handling they might pro-
bably guess, perhaps not; they would poise it in their hands, look at it,
smell it, try to cut it, perhaps, examine its metallic lustre, and it would
be very odd indeed if they could agree as to the composition of the alloy,
unless settled by an assay upon the balance.
Has it ever occurred to the reader that such processes as these go on in
Microscopy, and that it is necessary to carefully study the organ of vision
in order to gain a true insight into the object presented to us? On
reference to plate 1, it will be seen that the eye is a nearly spherical ball,
capable of many movements in its socket. It possesses an outer trans-
lucent covering called the sclerotic coat, ov simply sclerotica, which may
be seen at S. This is thick, horny, and opaque, except in its anterior
portion. .
This sclerotic coat envelopes about % of the eyeball, and in
6
common parlance is called the white of the eye.
The anterior transparent portion is ealled the cornea, and has the
shape of a very convex watch glass. It is through this membrane that
the light passes to the interior of the eye. The cornea and the interior
portion of the sclerotica are covered with a mucous membrane.
Behind the cornea is a diaphragm of annular form called the iris ; it is
coloured and opaque, the circular aperture in its centre, p being called
the pupil.
The iris, 7, serves the purpose of regulating the admission of light ;
it varies in colour in different individuals, and is the part referred to
when we speak of the colour of a person’s eye.
Behind the pupil is the crystalline lens, 7, having a much greater con-
vexity at its posterior surface than at the anterior.
The large posterior chamber is lined by the choroid coat,
and this choroid has in front of it a delicate membrane called the retina.
The choroid coat consists of a highly vascular membrane contain-
ing pigment cells, filled with an intense black mucus, called the
pigmentum nigrum.
The cavity behind the cornea is filled with a liquid called the aqueous
humour, having a refractive index approaching that of 1.3366, while the
larger cavity is filled with a transparent jelly, called the vitreous humour,
possessing a refractive index of 1.3379, enclosed in a very thin, trans-
parent sac, called the hyaloid membrane.
I have now described the principal apparatus of the eye, and may
take some of the parts in detail.
The crystalline lens is built up of layers, increasing in density inwards,
the effect of which is to diminish spherical aberration. This lens is
enclosed in a transparent capsule, held in position by an elastic mem-
brane. It can be changed in shape by means of a delicate muscular
arrangement to adapt its focus for near or distant objects.
THE HUMAN EYE. Xi.
As glass lenses of varying curves have different focal lengths, so by
altering the curves of the crystalline lens we are able to see objects
distinctly which are situate! in several focal planes. rn
The reader may have noticed that there is a near
point at which objects can be seen most distinctly ;
this point varies in individuals, but averages from
8 to 10 inches. As we move farther away from the
object, although diminished in size, it may be seen
more easily, and with less effort.
It would appear, then, that all objects are ren-
dered apparently larger, as they continue to approach
the eye, but a limit is soon found to this, as at a
distance of six inches distinct and easy vision is not
possible (except in very abnormal cases).
The reason of this is well-known—the anterior
focal point of «a convex lens when shortened
lengthens the posterior conjugate focus, so that when
an object is brought too near the eye the image of it
is projected behind the retina, and the crystalline
lens cannot accommodate itself to such extremes,
But we know that objects can be seen distinctly at
ereat distances apart, and it may be useful to demon-
strate how this is brought about.
The figure (1) represents a cross section of
the crystalline lens. The real mechanism of Fig. 1.
accommodation has been much disputed, but the results, as observed, are,
that the curvatures of the crystalline lens «re altered as the observer
adapts his eye to near or remote vision ; increase of curvature, of course,
shortening the focal length of the crystalline lens, and being better
adapted for near vision, while the shallower curve is necessary for
the distant view of remote objects. Helmholtz has shown that the
radius of curvature of the anterior surface of the crystalline lens
may be varied by means of the muscular arrangement, from 6 to 10
millimetres.
We may now cast another glance at
the iris. This apparatus is really a
continuation of the choroid tunic which
hes between the sclerotica and the
retina: it ends in front, in what are
called ciliary processes, as shewn in Fig.
2. The small muscular ring surround-
ing the pupil is called the sphincter
muscle.
Now, the principal use of the choroid
tunic, or rather the pigmentum nigrum
which it contains is to absorb those rays
of hght which have passed through the
Fig. 2. transparent retina, preventing their re-
flection, which would interfere with the distinctness of the image.
Xe METHODS OF MICROSCOPICAL RESEARCH.
By referring to Fig. 3, after Henle,
it will be seen that the chloride
tunic, the retina, and sclerotica form
the three outside rings, while the
centre is ramified by nerve filaments
and blood-vessels. (Fig. 3.)
These nerve filaments and blood-
vessels lie in the retina, which really
forms a continuation and extension
of the optic nerve ; it tonches the
outer circumference of the iris at the
front, and lies open as a cup-shaped
disc in the interior of the eye; it
receives the rays of light which have
passed in turn through the cornea,
aqueous humour, crystalline lens,
and vitreous humour, and forms a picture at the focus of these.
The nerve fibres of the retina are excited probably bya product of the
action of the light picture upon the visual purple, and the irritations
are transmitted to the brain by the optic nerve, producing the sensation
of vision.
The picture produced upon the retina has been compared with that
produced by a photographic lens upon a screen or ground glass ; but it
will be seen that the instances are not strictly parallel.
In the eye the rays falling upon the cornea do not again encounter air,
the picture is formed 7n the highly refractive substance, while in the
photographic image air intervenes between the screen and the lens, and
between the lenses themselves.
Then, again, the adaptation of the eye to various distances is obtained
by a process so dissimilar to that of the lens in the camera, that it is well
no comparison should be instituted.
The retina has been previously described as a delicate membrane lining
the choroid tunic, inside the sclerotica.
Now, if we make a section of the retina, we shall probably find its
structure very similar to the diagram. (Fig. 4.) I say probably, as I
have never met with sections which displayed the structure so well as
Max Schultze has indicated. He has described the various layers which
you see before you, as follows :—
Starting from the junction of the retina with the vitreous humour,
we have—
The layer of nerve fibres ...........0...45 a, | The outer granular layer aes
The layer of nerve cells...... .'.. ..... ...0. | A second fine membrane anaes eeneeee q.
Thepranwlar day ors seh oe) aes, eee ees c. | The layer of rods and cones...... . ......A.
The inner granular layer ......cs..c.ec0005 d. | Pigmentum nigrum of the choroid ,,,...%
The intermediate layer ...,,,...:,sc0ereeee 0
THE HUMAN EYE. Xl.
The retina is the terminal organ , 2.) f
of vision, all the apparatus in }iWt=4 ea iS
front of it being merely for the fi}
purpose of securing that an accu- |
rate image should be focussed ff
upon it. As to how the lumin- }j a
ous impres-ions yield to us such i yk. Rie ee
a definite idea of things isa ques- PRA gay “a
tion still under consideration,
many have tried to solve it, but
I am not sure whether we are
any nearer the mark than those philosophers who lived 2,000 years ago.
There are several curious properties inherent in the retina. By means
of the ophthalmoscope may be seen a point, a little out of the centre,
where the optic nerve enters the eye. This spo‘ is totally blind, it can-
not perceive a trice of light, and if the image of an object falls upon this
blind spot, that object is totally invisible. It is at this spot also where
the blood-vessels enter the eye, and ramify through nearly the whole of
the surface layers of the retina.
In the centre of the figure (3) you will see also a dark shaded portion
practically free from blood-vessels. It is a round, yellowish, elevated
spot, about 2th of an inch in diameter, and it is here that the sense of
vision is most perfect. It is called the yellow spot of Scemmering ; it is
not covered by the fibrous part of the retina, but a layer of closely-set
cells passes over it, and in its centre is a minute depression called the
fovea centralis. (Plate 7.)
In the above description points only have been touched which directly
bear on good or defective vision. On the other hand, enough has been
ad. anced to show that this organ is liable to imperfections which may,
and are, extremely liable to modify all our observations made over the
tube of the microscope.
_ In order to produce a picture upon a screen, a lens is not absolutely
necessary, if a diaphragm, perforated with a series of holes,
be placed in front of the electric lamp, the screen will be
decorated with as many images of the carbons as_ there
were holes in the diaphragm; but another illustration will
perhaps render this more evident. A smail hole pierced in the shutter
mo
TF,
of a darkened room (Fig. 5) allows of the passage of rays from a well
Si: METHODS OF MICROSCOPICAL RESEARCH.
NN ——
illuminated landscape, so that a small but inverted image is cast upon
the screen ; the further the screen is placed away from the aperture the
larger will the image be, though less distinct, and vice versa. The
picture produced is not so good as that formed by a lens, if is dark and
somewhat confused at the margin, and if the aperture is enlarged, there
is still greater confusion, until the image is finally lost.
Now, if we take an ordinary lens of glass and attempt to produce a
picture with it, we find the centre alone is plainly visible—the lens is
afflicted with what is termed spherical aberration, that is, the rays from its
periphery are brouzht to a focus in a different plane to those occupying a
central position.
Now, this fault may be illustrated by Fig 6.
Vig. 6. :
But although it is so easily shown in a diagram, a small amount of
spherical aberration is not so easily detected by the student. It appears
as a haze or fog of light over the object.
In the human eye this defect is not observable to any great
degree, as the peripheral or more strongly refracting rays are cut
off by the iris. Then, again, the curvature of the cornea is ellip-
soidal rather than circular, so that the rays farthest from the axis
are least deviated, while the two curves of the crystalline lens
correct, so to speak, the one the other; and lastly, this jens is of
such construction that its refractive power diminishes from the centre to
the circumference.
Another defect in the eye is due to the different meridians having
dissimilar degrees of curvature.
If a set of concentric circles be observed
with one eye, they are seldom all distinct
at the same time, and there is produced a
kind of Maltese-cross effect, not perceivable,
perhaps, in many instances with large
circles, but noticeable when drawn to such
a size that the outer one is about two inches
in diameter. (Fig. 7.)
This defect is called astigmatism, and
known to oculists as a common cause of
headaches. Spasm of the focussing appa-
ratus may derange the sphericity of the eye, Fig. 7.
and so affect vision. Strained vision is very subject to this. On the
other hand, the same apparatus may be paralysed, and ordinary vision
deficient, whilst the focussing of the microscope might possibly correct it.
THE HUMAN EYE. Xill.
Astigmatism has injuriously affected painters; Turner for instance,
whose later pictures are discovered to be slightly distorted, in
consequence of the power of accommodation or self-correction having
been lost from age.
In mieroscopic drawing, as with the camera lucida, the perspective
may be misrepresented, in consequence of astigmatism, and thus endless
disputes may arise even among the most careful observers.
We have now to deal with errors of refrangibility, and it will probably
have been assumed that the eye apparatus is entirely corrected for colour.
This is not the case, however, except when an object is in exact focus,
and the reason that the error due to refrangibility remains practically
unnoticed is that the distance between the focal point of the red and
violet rays is extremely small. The error due to refrangibility may be
noticed by means of the concentric circles already referred to; by
bright daylight adjust the eyes to some object twelve inches away, ard
without moving the eye insert at a distance of four inches a card inscribed
with black circles, when a yellow and blue colouring will be plainly
discerned.
In order that the
reader may thoroughly
understand the error
of refrangibility, the
picture afforded by
the passage of a solar
ray through a prism of
glass may be. thrown
upon ascreen, the rays
are deflected unequally,
the red least and the
violet most, as in
pies 6)
Fig.’ 3,
Fig. 8.
It may be advisable here to state that the degree of dispersion of the
rays of white hght depends upon the medium through which the ray
passes, and this amount of dispersion is measured by the distance of the
most prominent dark lines in the spectrum from each other. The
diamond disperses much less than crown glass, while the deflection of the
ray is greater ; but this is a subject beyond the scope of the present
essay.
_ Now, beside these errors, there are others to which the microscopist
should devote special attention; they are caused by small opaque particles
existing in the transparent media of the eye-ball. These cast their shadow
on the retina, and produce images which appear to exist outside the eye.
These extra-retinal images often appear as globules, bacteriod-shaped
bodies, or strings of minute pearls, and may be studied by directing the
eye to a sheet of strongly illuminated opal glass, through a small aperture
made with a fine needle in a piece of thin ‘blackened cardboard. (Fig. 9.)
XIV. METHODS OF MICROSGOPIGAL RESEARCH.
When the microscope is used in a vertical position, these globules
often gravitate to the centre of the cornea, and even after prolonged use
of the inclined tube an observer may often be perplexed by the layer of
mucus, or a lachrymal discharge covering the surface of the cornea.
Just a few words as to colour
perception. Colour is a special
sensation excited in the retina by
rays of a definite wave length, and
the reason why certain objects are
presented to our view with colour
is that when white hght falls
upon a given surface, some is
absorbed, the remainder being
reflected. If the green rays are
reflected, then the object appears
green, and if the red rays are
alone reflected, then the object
will be red.
The generally accepted theory of
colour perception is based on the
assumption that three kinds of
nerve fibres exist in the retina, the
excitation of which produces sensations of red, green, and violet, and that
modifications of these three sensations yield all intermediate tints.
Fig...9,
This theory will explain some of the phenomena of colour blindness—
if the nerve fibres which should give their special sensation are paralysed,
or are wanting, the sensation only of the complementary tint will be
transmitted with all the defects of the eye. It must not be forgotten
that many phenomena consist more in er-ors of Judgment than in absolute
error of form or sensation.
Now in regard to errors of Judgment, we must admit that all our esti-
mations are made by comparison. In magnitude we are cuided
by the size of the retinal image as determined by the visual angle—
for position we must have some starting point; and as for distance,
every one knows how delusive an inexperienced estimate of thisis. At
sea, a landsman could not judge of the distance of a passing vessel to a
few miles, nor could we form any accurate idea of the size of any object
emitting practically parallel rays unless we had so mething to compare it
with.
We now come to a point which has been much disputed in the study
of microscopy—binocular vision.
The two eyes move together as a system, so that we direct the two
lines of regard to the same point in space and consequently see but a
single image ; but it is possible to see two—if one eye be displaced a
little with the finger two images are seen, while if the other be displaced
to a corresponding degree the one image is restored.
THE HUMAN EYE. x Vie
The value of binocular vision may be easily ascertained by experiment.
When a picture is presented to the retina of each eye, the compound °
picture is much brighter than when one retina only is employed.
To each point of the retina of one eye there is a corresponding point in
the retina of the other, and impressions produced on one of these points
are in ordinary circumstances indistinguishable from a similar impression
produced on the other.
When both retin are similarly impressed, the general effect is that
the impressions are more intense than when one eye only is employed; and
we also get a perception of relief, that is of form in its three dimensions.
Take two A eyepieces and look through them to the sky, so that two
distinct circles are seen ; now bring them together so that one circle over-
laps the other, when this overlapping bi-convex portion will be found
double the brightness of the remaining portions of the circles.
We are indebted to stereoscopic vision for the perception of relief or
form in three dimensions, which occurs when the images falling upon the
corresponding points of the two retine are not exactly similar. In look-
ing at an object with both eyes the rays do not run parallel from one side
of the object to the eye on that side, but the right eye centres itself to
the left side of the object and v/ee-versa. This may readily be seen by
holding up a finger between our eyes and the wall, and looking at the
latter. Two tingers may be seen projected on the wall, one of these is
seen by the right eye and the other by the left; but our visual impres-
sions do not inform us which picture is formed by either eye in particular.
Now, while steadfastly looking at the wall, close the right eye and the
left finger will disappear, while on shutting the left eye, the right finger
is rendered invisible.
When two similar pictures are presented to the eyes, the impres-
sion is more vigorous and looked at with greater ease than when ove
eye only is employed ; vision in this case is called pseudoscopice.
Binocular vision should be employed wherever
practicable ; it will be found much less trying to the
eyes than monocular efforts.
I have now mentioned the leading features of the
human eye, and shown that it is extremely liable to
imperfection, and, being so, strict attention to details
is demanded from the microscopist.
Fig. 10.
Now, although the human eye is such a_ wonderful instru-
ment, there are many problems it is unable to solve without
XVI. METHODS OF MICROSCOPICAL RESEARCH.
extraneous help. Take, for example, the bunt ot wheat,
Tilletia. caries (Fig. 10). With the unaided eye, you
will be able to discern nothing more than a_ black
dust, the various details having to be made out by other |
means. Then again, with objects so minute as the diatom,
Amphipleura péllucida (Fig. 11), the object itself is almost
invisible to the unassisted eye, to say nothing of the beautiful
carvings with which the valves are embellished, and which
exact for their elueidation the most perfect lenses with which
we are acquainted, and the most accurate manipulation of the
illumination. You may, indeed, see the contour of many
forms of diatoms without extra optical assistance than that
afforded us by nature, but not much more than this, as if
the eye is approached too closely the picture falls behind
the retina and is lost.
If we take a very much enlarged picture of the diatom,
Pleurosigma angulatum, it illustrates in a remarkable manner
how errors of observation are likely to creep in. It is hard
to believe at first that the white circles which are seen are
not hexagons, but are in fact true cireles, which elose investi-
gation will prove.
I have already mentioned the fact that starting with the
distance of most distinct vision, continued approach to the
eye finally renders the object invisible, the rays being thrown
behind \he retina, the mechanism of accommodation being
insufficient to produce a curve deep enongh to bring the
picture to a short conjugate focus.
This can, however, be done by interposing a lens or lenses
between the object and the cornea, so that a virtual image of
the object is seen. These lenses form either a simple, or a
compound microscope.
THE PREPARATION OF ANIMAL TISSUES. XViL.
THE PREPARATION OF ANIMAL TISSUES. |
Most animal tissues require hardening ; a few, such as bone and tooth,
require softening, whilst certain structures are either destroyed, or the
features we wish to see distorted, by either process, so that we have to
examine them in media which we call indifferent, such as 37% salt solu-
tion, etc. Besides the above, we have special operations, such as Injection
of blood-vessels, rubbing down of tooth, bone, and so forth.
We will first describe the hardening processes, prefacing our remarks
by giving a few general directions. The requisite tissues have to be.
obtained from the newt, frog, pig, sheep, calf, ox, rabbit, cat, dog, horse,
etc. We have further to requisition the water-beetle, crab, salt water
mussel, skate, and tadpole. further, we have to procure newly-born
animals and foetuses.
In hardening tissues from the above, as a general rule we must secure
penetration of the Jiquid by placing the tissues in abundance of lquid—
100 times their bulk or more, and dividing the tissues into sufficiently
small pieces. The latter object is attained by allowing a quarter of an
inch, and not more, for the fluid to penetrate. Thus, in placing a solid
organ, such as liver or kidney, in hardening fluid we should cut it into
half-inch cubes, then the deepest part of the cube would be a quarter
of an inch from the surface. Jor membranes and organs which have no
part a quarter of an inch from the surface such as omentum, trachea, etc.,
we «divide the parts for other objects, it may be, but not to reduce them
for penetration of the hardening liquid.
The tissue must be as fresh as possible. Parts which have to be treated
by the silver or gold processes must be taken within half an hour after
death, or the parts affected by our re-agents will have ceased to be sus-
ceptible. The time of year also has much to do with this, summer and
hot weather being a worse time than the cold weather of winter. No
tissue can be placed in its preservative medium too early. All foreign
inatter such as contents of bowel, etc., must be removed by #7 salt
solution. After a fluid has become fouled by the tissues placed in it,
it should be changed. All tissues placed in chromic acid solutions must
be examined daily after a few days to prevent them becoming brittle and
spoiled. Chromic acid is an excellent medium, but it renders the tissue
brittle, and spoils it if kept a day: or two too longinit. Then, again,
different tissues in the same medium require separate testing. Some may
be hard enough and require immediate removal, whilst others may remain
longer. No tissue should be allowed to remain until it is quite hard in
the chromium preparations, if we wish to finish the hardening in spirit,
as is commonly the case, but should be removed when it has become
tough, and has still plenty of elasticity. In changing a tissue to complete
its hardening in spirit, we must first of all wash away all its former harden-
ing medium by soaking it in plain cold water, frequently changing the
water during the twelve or twenty-four hours we keep it there, so that
XVIll. METHODS OF MICROSCOPICAL RESEARCH.
the last washings may be colourless. We must not put tisstes thus
prepared direct into spirit, but first place them in methylated spirit and
water, half and half, for twenty-four hours, then in meth: spirit pure.
In some cases such as testes, brain, tonsil, etc., we require to transfer
them from the common spirit to absulute alcohol, before making sections.
The object of hardening is to shrink the tissues, but in shrinking them
we have to shrink them uniformly, and therefore, gradually ; therefore,
a fluid that would harden and not penetrate, would harden and shrink
the tissues nearest the surface, and perhaps allow the interior to soften
and rot. Asa rule, we must commence with weaker, and advance to
stronger, solutions, for the purpose of penetration, and even shrinking.
Not only so, but we often have to commence with a fluid remarkable for
its penetration—such as Miiller’s Fluid—which penetrates to great depths,
but is slow in its hardening capacity, requiring weeks in doing so, but
frequently not hardening some tissues, sufficiently, at all. We must
keep a small book, with copious notes as to the kind of animal, the
tissue, the date and manner of its death, the nature of the fluids it is in,
or has already been in, dates of changing, or of substituting fluids, ete.
Each bottle should be labelled with a letter or number, or what is better
in some cases, a letter and number, any sufficient mark, in fact, which
may have its corresponding mark in our note book. Mere labelling of
the bottle, and making notes upon it, will not do for many reasons. For
extra distinction, we may either wrap the tissue in linen, and tie a label
to the linen, or we may place special tissues, easily distinguished loose,
and in the same medium.
With a further remark, that no hard and fast line can be drawn in the
matter of ¢¢me any substance may require to be in a fluid before its trans-
ference to another fluid, but in most cases the operator must use his judg-
ment, which, after all, requires some experience, we will now give a
list of tissues arranged under the hardening fluids. It will be found
that the same tissue will appear under more than one preparing medium
in many cases, because the various elements in a tissue may not be all
demonstrated by treatment in any one fluid ; thus, if we wish to shew
the cornea corpuscles and nerves, we treat a cornea with gold, whereas, if
we wish to see its cell spaces, we treat it with silver. So that the same
tissue, cornea, will be found under gold process and silver process: the
same obtaining between absolute alcohol and the chromium preparations,
and still further between the sarcous substance preparations themselves.
Curomic AcIp.
We make a 1% solution with common water, and reduce it to a fourth,
sixth, or any other percentage solution we require.
Bone deprived of its muscles, but not of its periosteum, is steeped in
very weak solution, then in stronger solution of chromic acid, com-
mencing with a tenth per cent. and rising to a half, through a period of
ten days. It is then decalcified by steeping in chromic and nitric fluid
until a needle can be pushed through it. Then it is washed and trans-
ferred to spirit, A tooth may be treated the same
THE PREPARATION OF ANIMAL TISSUES. XIX,
Muscize.—A bit of muscle from an animal that has been dead a few
hours is steeped in a small quantity of a 4 °/, solution for a week.
The cleavage of its sarcous substance is shown by teasing a bit in
glycerine. }
Nerve.— Harden a piece of meta carpal nerve of a horse, or sciatic
nerve of a smaller animal, for ten days ina ¥ solution. Stain a bit
in logwood, then tease it in glycerine thoroughly. This shows its
connective tissue.
CuHRomic AcripD AND SPIRIT.
Mix one part of % % solution of chromic acid with two parts of
methylated spirit. This should be done when required for use.
The following tissues may be placed in this, then transferred to spirit.
The time required must be judged according to directions already
given ;—
The whole of one cornea, to show stratified, epithelium ; a piece of
small intestine, to show non-striped muscle ; heart and pericardium of a
small animal ; small arteries and capillaries from the brain of a sheep,
after scraping away the brain-substance ; middle-sized artery—such as
metacarpal of the horse ; trachéa and lungs. ‘These are gently injected,
then immersed in the fluid. |
_ The lips, tongue, salivary glands, tonsils, cesophagus (distended and
tied), stomach (after gently washing away its contents with 3 7% salt
solution), small and large intestines, liver in half-inch cubes, ureter
and bladder (distended), ovary, fallopian tubes, uterus (distended per
vaginam) may be placed in the solution.
Besides the above, which may be taken from either a dog, cat, or
guinea pig, the following should be obtained :—The thymus gland of an
infant ; skin of scalp, finger and palm of hand, sole of foot from the
human subject ; also a nail. The eye of an ox divided transversely just
behind the cornea for the ciliary muscle, sclerotic, cornea, and iris; also
the choroid and retina. Of course both halves have to be used. The
prostate gland and penis of a guinea pig. The cervix uteri of a cow.
Mammary gland of an animal near the full period of gestation. The
placenta ofa cat, or guinea pig. The umbilical cord, which must be cut
into pieces an inch long, and hardened for two days in MiiJler’s fluid
before being placed in the present medium.
With all the above the tissues must dazly be examined, after the third
day, and each transferred after it has become tough. Moreover the fluid
should be changed after the first twenty-four hours, whether changed
afterwards or not. When many different tissues are in the same jar, the
quantity of fluid must be such that the uppersurface of the tissues extends
half way up the entire fluid, that is to say, the stratum of tissues and
stratum of clean fluid over them had better be of equal depth.
BICHROMATE OF PorTass.
Make a2 solution of bichromate of potass, with ordinary water.
Meso-rectum of Cat. Pin this out on cork, and float it cork upwards
on the solution for seven days.
be METHODS OF MICROSCOPICAL RESEARCH.
Liver. After injecting the portal vein with blue gelatine mass, and
the hepatic artery with carmine gelatine mass, the liver may be hardened
in the solution to toughness, and, of course, finished in alcohol.
Spinal Cord of Ox. Pieces an inch long may be placed in the solu-
tion—frequently changed—from three to five weeks.
Spinal Cord of Ox, Horse, or Sheep. If pieces about an eighth of an
inch long be macerated two or three days in an eighth per cent. of the
solution, the anterior horn of the spinal cord snipped out, with scissors,
and teased in carmine solution, then pressed with a cover glass, using
Farrant’s medium, will show the isolated multipolar nerve cells very
beautifully. We may isolate the sympathetic nerve cells of the frog in
the same manner.
Cornea of Cat, Rabbit, or Guinea-pig should also be hardened in a two
per cent. solution for ten days. The lens in a one per cent. solution for
one week.
Ovaries of the Cow in very small pieces should be macerated in very
dilute solution to isolate the large, branched pigmented cells of the
Corpora lutea.
AMMONIUM BICHROMATE.
A two per cent. solution made with ordinary water may be employed.
This solution is preferred by many to the potass salt solution. It is
used in the same way. Columnar epithelium may be prepared as a per-
manent specimens by placing a piece of fresh intestine of dog, cat, rabbit,
etc., in a one per cent. solution for two days; then steeping an hour or
two in water and scraping off the epithelium and staining. The cells
have to be separated with a needle, and may be mounted in Farrant’s
medium, or in glycerine jelly.
CHROMATE OF AMMONIUM.
A five per cent. solution is used.
If a newt’s liver (in small pieces) and pieces of the small intestines
be placed in the solution for forty-eight hours, the liver cells and
columnar epithelium may be obtained, as in the case above-mentioned.
The goblet cells of Klein can be beautifully preserved in glycerine jelly
in this way. The mesentery of the newt may be placed in the solution
at the same time, and taken out after twenty-four hours. This shows
the non-striated muscle fibre beautifully. The isolated gastric glands of
a small mammal may be obtained in the same way by placing bits of
the fresh mucous membrane for three days in the solution. The testes
of the newt should be placed in the solution for twenty-four hours, then
cut into, and their contents squeezed out on to a slide. The spermatozoa
are thus obtained as a permanent preparation.
Another important use of the above solution has been pointed out by
Heidenhain. If small pieces of kidney be placed in the solution for
forty-eight hours (the cortex should be chosen,),the preparation shews
the cells of the uriniferous tubules and their peculiar clearly as
no other method, probably, can shew them.
{HE PREPARATION OF ANIMAL’ TISSUES: XX1.
Miuuer’s Fuurp.
This is made by dissolving 25 grms. of Potas bichrom’; and 10 germs.
Sodae Sulph. in 1000 c.c. of water. —
Miiller’s fluid has great penetrating power. It hardens slowly, taking
it may be five to seven weeks. It is useful as a commencing agent to be
followed by another of greater shrinking power, such as chromic acid and
spirit solution, common alcohol, etc. Very even shrinking may thus be
obtained. For example if we cut out the fresh nasal septum and place
it for two days in Miiller’s fluid, then for a week in Chromic
acid and spirit solution, afterwards in weak, then in pure methylated
spirit, we get the olfactory epithelium in excellent preservation.
After the above explanation the reader will have no difficulty with
the following delicate structures namely :— Developing tooth, the adenoid
tissue of lymphatic gland, spleen, thyroid gland, supra-renal-capsules
(of the horse, by preference) sympathetic ganglion, olfactory epithelium,
cochlea, testis, epididymis and vas-deferens, ovary; human placenta, ete.
MU.Luer’s FLuip AND SPIRIT.
Take three parts of Miiller’s fluid and add to it one part of methylated
spirit and keep it in a dark place. The mixture should be made only as
required.
The above is especially useful for the central nervous system. The
removal of the brain and spinal cord without injury may here be
described. Immediately after death the skin is removed, or at least the
skin over the back and neck. - Then we separate the neck and head from
the trunk about the middle of the neck. Next we clear away the
muscles on each side of the vertebral spines and chp away every spine
as close as possible with scissors or still stronger shears, such as bone
forceps. Next with ordinary forceps we grasp the lamine, which cover
over the spinal cord, one lamina at a time, and break it outwards by
inserting one blade of the forceps within the neural canal, the other on
the upper surface of the Jamina. We advance down the spine breaking
the laminz outwards, right and left till all the cord with its membranes
is exposed. We deal with the head part likewise by breaking off, bit by
bit, the top of the skull, inserting one blade into the interior, of course,
after clearings away the skin and muscles.
The spinal cord and membranes of a cat, dog, or rabbit should be care-
fully got out, and suspended in a deep, narrow vessel. The fluid should
be changed at the end of 24 hours, then after a week. At the
end of this time, divide into pieces an inch long, and continue the harden-
‘ing for another week or two, as may be required. It may be replaced by
a two / solution of bichromate of ammonium for two weeks, and the pieces
preserved in spirit, or by Hamilton’s method (choral hydrate, 12 grains ;
water, 1 ounce). The cerebellum, cerebrum, and, of course, the medulla
oblongata may likewise be hardened. In the case of the two former we
have to divide into suitable pieces for the sake of perfect penetration.
The tendo achilles of the calf, and the metacarpal nerve of the horse,
each in inch long pieces; also the posterior half of the eye-ball of a pig
(for the retina) may be hardened with advantage in this fluid.
XX. METHODS OF MICROSCOPICAL RESEARCH.
ABSOLUTE ALCOHOL.
This should have a specific gravity of 0°795. It hardens in 24 hours,
with much shrinking. It is used for secretory glands notably the
pancreas, which must be placed direct in it, or the gland may spoil by
partial self digestion. Therefore we may place the salivary glands, the
lachrymal glands, pieces from both ends of the stomach for the gastric
glands, the pancreas in pieces, etc., in it at once.
If we inject the lymphatic gland of a horse, ox, or smaller quadruped
with two % Prussian Blue fluid by Klein’s method,—introduce a glass
pipette filled with the fluid into a lacteal near a mesenteric gland and
blow the solution into it,—then place the gland in absolute alcohol, we
have the lymph sinuses well injected. The muscle structure of the beetle
or crab is shewn well by placing a beetle, or the amputated limb of a erab,
for a week in absolute alcohol. temperature of 40° C. iy st tag ai
Dr. G. Sims Woddheaa’ S Miss : —
_ Take of Carmine (pure), 4 parts, by Weight.
Liq. ammonia, 8 parts, by measure.
Gelatine (Cox and Coignet’s), 10 parts, BY. weight,
Distilled water, 100 parts, by measure.
Put the carmine in a mortar, and pour on the ammonia, when an
almost black paste will be formed, if the carmine is pure; pour on the
water, and set the solution aside to filter. Place the gelatine in a narrow
glass jar, and add sufficient distilled water to cover it, and allow it to
stand till the gelatine is thoroughly softened. Warm the carmine solu-
tion in a pan of water (kept nearly boiling on a gas jet or near the fire),
and add the gelatine ; stir thoroughly, and add a ten per cent. solution
of acetic acid, drop by drop, until the alkalinity of the ammonia is
neutralised, and the fluid even slightly acid. The point at which this
takes place will be recognised by the pungent odour of the ammonia
becoming gradually lost, ‘and that of the acid substituted, and the fluid
loses its bright carmine, transparent colour, and turns a dull brownish red.
We have given the above formule for making the same thing for
several reasons. First of all, the operator will be struck by the con-
trast, which is so slight, but which does exist. We have given the three
in their order, reckoned by their date of publication. There would
be no reason whatever for not adhering rigidly to Carter’s formula, but
each operator thinks he sees a better way of neutralising the ammonia.
With the exception of the change of colour test, we prefer Stizrling’s
method, which, however, is greatly improved by making a diluted acetic
acid solution, by adding the acid to a dram or two of water, when the
pouring to or adding is more easily controlled. It will be noticed that Dr.
Woodhead takes a ten per cent, solution.
BivE Mass.
This is made by adding soluble Prussian blue in place of UK carmine.
Take of Soluble Prussian blue, 4 drams.
Gelatine, 4 oz.
Distilled water, 20 oz.
Treat the gelatine the same as in making the carmine mass, using half
the water ; then add the Prussian blue dissolved in the other half of the
water, keeping both solutions hot, and constantly stirring whilst cooling
is going on.
InsectINGa APPARATUS.
The most usual way of injecting the blood-vessels is by means of the
ordinary injection syringe. This requires a great amount of practice.
The animal has to be kept in hot water; the mass has to be kept hot
usually in a separate vessel, and time has to be allowed between each
xX: METHODS Of MICROSCOPICAL RESEARCH,
syringeful, for the fluid to penetrate. Then, again, if air gets in on
introducing the point of the syringe into the socket of the pipe that is
tied into the artery, the fluid will not run at all.
The constant pressure apparatus of Ludwig, now that a simple and
thoroughly efficient method of getting the constant pressure by means of an
ordinary Higginson’s syringe, as discovered and described by Fearnley,
will take the place of the syringe, and of every other method in future.
No practice is required with this simple contrivance, beyond introduc-
ing and tying in the nozzle in the aorta. There isa bath, having a
Ye
—— LLL
ANN Ee
shallow part for the animal to lie in, and a deeper part for the Woulffs
bottle, containing the injection mass, to standin. A large (40 ounce)
Woulff’s bottle, with three necks, is fitted with three perforated india-
rubber stoppers. The middle stopper is perforated with a glass tube,
which goes to the bottom of the bottle. Each of the others is perforated
with a glass tube, the depth of the stopper only, and standing above the
THE PREPARATION OF ANIMAL TISSUES. XXX.
stopper sufficiently to admit of a piece of indiarubber tubing (such as is
used with infants’ feeding bottles) being fixed upon it. The Woulff’s
bottle containing the mass, has two necks, fitted with indiarubber
stoppers. One neck admits a piece of glass tube, which goes quite to the
bottom of the bottle; the other admits a short piece of tube, the depth
of the stopper only. The diagram shews all further detail. The
apparatus is made by Messrs. Swift & Son, 81, Tottenham Court Road,
London, W.C.
FEARNLEY’S CONSTANT PRESSURE APPARATUS.
The mercurial manometer allows five inches rise of the mercury in the
ascending arm—therefore, five inches fall of the descending arm—though
four inches will do.
To inject an animal—a rabbit, for instance,—proceed as follows :—
Fill the bath with water, and heat the water with a Bunsen’s burner to
100° Fah. or so. The Woulff’s bottle containing the mass should be filled
and thoroughly stoppered Then chloroform the rabbit and make an L
shaped incision into the thorax, so as to expose the heart and aorta.
This is done by cutting up the middle line of the sternum (breast-bone) as
far as the root of the neck nearly then making a second incision at right
angles to this, to the rabbit’s left. A triangular flap is thus made, and
the heart enclosed in the pericardium exposed. Having cut through the
pericardium, seize the apex of the heart with a pair of forceps and snip
it off, then the heart’s apex appears as in A, Fig. 2. That is to say, the
right and left ventricles are opened and the animal instantly bleeds to
death.
The opening in the right ventricle, leading to the pulmonary artery
has a erescent shape or slit-like appearance; whilst the opening in the
left ventricle, leading to the aorta, is ronnd. Therefore, if we wish to
XXXIL. METHODS OF MICROSCOPICAL RESEARCH.
inject the entire arterial system, we insert our nozzle into the round hole,
but if we wish to inject the pulmonary system only we choose the
crescentic slit.
Either glass nozzles, or those shown in Fig. 2, are to be inserted into
one or other of the two holes (usually the round one for injecting the
entire arterial system with carmine and gelatine mass). We can now
either tie the artery only, or we can tie the: whole heart substance. In
either case a ligature of floss silk is to be passed round (the artery or the
entire heart) and tightly tied and secured. Before proceeding further,
we wash out the cavity of the thorax of all blood to keep our
bath-water clean, then we lift the animal into the bath and there let it
remain ten minutes or so to get well warmed. It is a good plan to slit
open the entire abdomen in the middle line, so as to allow the warm
water to freely get around the abdominal contents: the mass thus gets
into every organ and into every part of an organ evenly.
We now connect the pressure bottle with the manometer and with the
Higginson’s syringe, as shown in the figure, also with the mass bottle.
The tube of the mass bottle which is to convey the mass away from the
bottle is now clamped, as shown at C Fig. 2, and must never for an
instant be allowed to get out of the warm water into the cold air.
Having our small basin full of water, we now squeeze the Higginson’s
syringe, watching the manometer, to raise the mercury half-an-inch.
This done, we remove the clamp from the efflux tube, and the red fluid,
after driving out a few air bubbles, begins to flow out, we, at once, make
the connection, and all quicksands are passed if we have tied in our
nozzles properly into the artery and the connecting part, and fastened
in our stoppers thoroughly into our Woulff’s bottles.
Our task is easy now: all we do is to seize the head of the animal,
which should be to our left, with our left hand to watch the pale gums,
tongue, and eyelids become suffused with a pale blush which gradually
deepens, whilst we gently squeeze and relax the barrel of the syringe and
elance at the mercury from time to time. When the mercury has risen
four, or at most five inches, the whole animal will be completely in-
jected : the visible mucous membranes and bowels will be dark red and
much swollen.
We now remove the animal, and place it in ice cold water or under a
common water tap for an hour or two, and divide it into parts as re-
quired,
This method of applying pressure is wonderfully delicate; thus, whilst
we can raise the mercury in the manometer almost imperceptibly, one
entire squeeze of the barrel raises the mercury one inch,
——— ts
HOW TO PRESERVE BOTANICAL SPECIMENS. XXXIli.
—
HOW TO PRESERVE BOTANICAL SPECIMENS.
Botanical specimens can, with great advantage, be cut fresh as they
are gathered. This is not always convenient, however, so that we re-
quire a preserving medium. Preserving them is simplicity itself, as all
we require is to place them in equal parts of methylated spirit and water,
where they may remain for any length of time.
ON ANIMAL AND VEGETABLE SECTION CUTTING.
No part of histological work has undergone such a rapid change as the
so-called ‘section cutting.” Almost within the last twelve months
changes have taken place, which have rendered the art almost ridiculously
simple, if one may be allowed the expression. By means of Cathcart’s
microtome and a common plane iron, the most unskilful and unpractical
can cut sections of animal and vegetable tissues, of exquisite thinness, at
the rate of sixty or seventy per minute. We shall mention other micro-
tomes, and we shall have to point out the short-comings of each. Indeed,
the one we have mentioned is, like all things human or of human origin,
not absolutely perfect.
Most tissues, especially animal tissues, are now cut by the freezing pro-
cess: cutting by hand and razor is practically obsolete: cutting by im-
bedding and the well-microtome of Stirling is still in vogue, and, in some
cases, such as in wood sections, will probably remain so. Speaking
generally, however, animal tissues are cut with a freezing microtome.
We now pass on to notice the four principle freezing microtomes, and
in doing so, it will be best to take them in their chronological order,
PRoFESSOR RUTHERFORD’S MICGROTOME.
This is Stirling’s original well and screw-microtome, plus an ice box
arrangement. It is used by filling the ice box with well-powdered and
mixed ice and bay salt, equal quantities. Whilst freezing is going for-
ward the well may be covered with felt. One or several tissues can be
cut at once, either with a Rutherford’s knife, or, what is now found to
be far better, a plane iron. By a plane iron, we mean the iron taken out
of a carpenter’s smoothing plane. Theiron must be 27 inches broad : they
XXXIV. METHODS OF MICROSCOPICAL RESEARCH.
cost one shilling and sixpence each, and are either used with or without a
covering of wood. When double-faced with wood, the handling of them is
more pleasant, but it does not add to efficiency.
————
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The iron must be
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In sharpen-
g, must be taken to rub the entire length of the cutting edge —
evenly. This is best done by taking care to rub the edge on the stone
in such a way, that every portion of its length is upon the stone at the
same time.
In stropping, it will be found most convenient to rest the
plane iron against a-table edge, and push or pull the strop over it,
HOW TO PRESERVE BOTANICAL SPECIMENS. pt 9h
The advantage of the Rutherford freezing microtome is that it can be
also used as an ordinary Stirling’s microtome for imbedding in carrot or
wax. Its disadvantage is the same as that of ice-freezing machines
of whatever description: that it is cold, disagreeable work filling in the
ice and salt, and the former is not always to be obtained, and when once
charged, cutting must follow, or the ice melts and gets spent.
Mr. C. Baker, 244, High Holborn, W.C., sells an excellent Ruther-
ford’s freezing microtome, which, of course, must have its cutting face
covered with plate glass.
WituiaMs’ Freezinac MICROTOME.
This is made by Messrs. Swift & Son, 81, Tottenham Court Road,
London, W.C., who also make a registered knife carrier, which carries
the blade of a razor: the whole goes under the name of ‘‘Swift’s Knife.”
Until the plane iron was thought of, Swift’s Knife had the field all to
itself most undoubtedly, and there will still be those who will prefer it to
the plane iron.
This freezing microtome must be used either with Swift’s knife or some
contrivance of a similar nature. This combination has this great advan-
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tage: that in winter, when ice is plentiful, the machine is charged, and
freezes strongly for an hour or more. For class work this is excel-
lent: the attendant charges the machine just before the class meets, and
XXXVI. METHODS OF MICROSCOPICAL RESEARCH.
the demonstrator cuts a hundred sections of any prepared tissue in a few
minutes. If he wishes to cut another specimen, he clears away the first,
and clears out the grooves on the top of the section carrier with the back
of a knife ; then he places his specimen upon the machine, and paints
it round with gum solution, and the whole freezes fit for cutting in one
minute or so. With very little practice, it is quite easy to cut fifty
excellent sections of each of fifteen or twenty specimens with one charge
of ice and salt.
To manage Swift’s knife, we proceed thus :—First take the blade away,
and lay it flat upon a smooth hone well oiled, and rub it first on one side,
then the other, until the entire edge on either side is ground by the hone
at once. The writer rubbed over twenty hours before this was accom-
plished with the razor blade of his Swift’s knife. Both sides of the
blade are ground quite flat, to begin with, not hollowed; but cutlers
either cannot or will not grind a blade with its back and its edge per-
Jectly parallel, so that this has to be done by one’s self. Having ground
the knife blade, we fix it in the handle and strop it. We then take off
the handle and fix the blade in the carrier in such a way that the edge
must be perfectly level with the top of the microtome, and on a much
lower level than the back. This position of the knife in the frame is to
the last degree essential, and we effect it thus:—First place the knife-
blade in the frame, and lower the screws which the edge of the blade
rests upon, so that the edge is lower than the back a good deal. After
making it firm, we complete the levelling by freezing a piece of tissue,
and taking away a thick section, cutting away from us, with the knife in
the frame just as we have put it roughly. We now place each end of
the blade alternately against the same part or bit of the frozen tissue, and
raise or lower either end by screwing either of the two screws nearest to
us. All is now complete, and we cut away section after section by
lowering the knife edge for each fresh cut by giving the screw furthest
away from us a part of a revolution.
To Fitt an Ice MIcROoTOME. ©
Get a piece, or pieces, of ice the size of two closed fists, and the same
bulk of either common table salt or, what is better, bay salt. Powder
both, and thoroughly mix them. The ice is most readily reduced to fine
powder by being surrounded with flannel and bruised with a broad-faced
hammer, or a carpenters mallet. Fill in the mixed ice and salt and press
it well down, but take care that the trough of the microtome is not so
full that the top touches the ice and salt. The top is to be placed on the
microtome and screwed fast. In winter the machine, after being charged,
is ready for freezing in five minutes or so; in summer it may be ten
minutes or more. Freezing proceeds, as we have before said, for an hour
ortwo. The waste pipe at the bottom of the microtome is to be connected
by caoutchouc tubing, with a basin to receive the melted ice.
HOW TO PRESERVE BOTANICAL SPECIMENS. XXXVIi.
The disadvantage of Williams’ microtome is, that, like all ice micro-
tomes, it is disagreeable to charge even when ice is plentiful, and cutting
must take place at the time the machine is charged ; that is to say, if the
operator is called away, as in medical practice often happens, his ice
charge melts and has to be renewed.
FEARNLEY’s EtHEeR FREEZING MICROTOME.
Dr. Groves suggested the conversion of Williams’ ice freezing micro-
tome into an ether freezer. This is now called the Grove-Williams
microtome, and is made by Messrs. Swift and Son, and used with Swift’s
knife.
For those whoare not made ill by the inhalation of atmospheric air
charged with ether, the best and simplest ether freezer for use with Swift’s
knife is Fearnley’s ether freezing microtome. This is simply the top
Ze
of the Grove-Williams’ microtome, supported by three or four legs.
The ether nozzle is immediately under the frame of the glass plate,
and the bottle of ether stands beside the machine on the table as
shewn in wood-cut. Fearnley’s microtome is also made by Messrs.
Swift and Sor.
CaTHcART’s MIcROTOME.
This is an ether-freezing microtome for use, either with a stout razor,
or with a plane iron. Cathcart’s invention, used with a plane iron, for
- XXXVILL. METHODS OF MICROSCOPICAL RESEARCH.
cheapness, simplicity, and efficacy, cannot be approached by any ether or
ice microtome we know of. Its cost is only some fifteen or sixteen shillings,
and is, therefore, well within a student’s means. The plane iron costs
one shilling and sixpence ; and Messrs. Richardson, chemists, Leicester,
sell methylated ether at one shilling and fourpence per pound, which
answers admirably. With the expenditure of two drams of ether, the
operator can cut sixty or seventy sections in almost as many seconds,
every section being of exquisite thinness.
A little gum solution is first placed on the plate, and almost frozen :
then the tissue to be cut is placed upon it, and surrounded with gum
solution, and the whole frozen. The tissue is elevated to the knife by a
very small fraction of a revolution of the screw with the left hand,
whilst the right drives the plane iron. The iron must be held with the
edge far below the level of the rest of the iron, and the screw movement
and the push of the iron movement, must take place alternately. When
a mass of sections has accumulated on the iron, it must be floated off into
a saucer of water. After freezing and cutting about half-a-dozen speci-
mens, the operator will startle himself with the rapidity of his own
movements, To anyone used to working with mechanics’ tools, the feel
of the iron travelling over the glass and cutting through the tissue as
through cheese, is extremely pleasant. We could like to see the screw
of this microtome made much thicker, and the threads finer, and the
head of the screw half as wide again in diameter. With these slight
improvements, in our opinion, the microtome would be absolutely
perfect.
ase 7
i
phosphorus, monobromide of naphthaline, and others; but it is uny ©
necessary to enter into details concerning them, since the desired effects “=
have recently been obtained by Dr. Van “Heurck, who has succeeded in
. providing an admirable substitute for Balsam in gum-styrax, which yields
the best possible results. It will probably be found that Diatoms moun-
ted in gum-styrax are less liable to accidents than Balsam ‘“‘ mounts,”
as the latter becomes resinous in time, and the covers are liable to
“spring,” the result of which is the appearance of prismatic colours
in the Balsam, which are not only a great eyesore, but sadly deteriorate
the slide. Gum-Styrax may be considered absolutely permanent and
unalterable. Purified Styrax contains a granular substance, which must
be removed by dissolving it in chloroform and filtering the solution.
The solution thus obtained is used in the same manner as Canada
Balsam. Styrax solution is even easier to work with than Balsam, and
air-bubbles are not produced in it by the application of heat. The crude
Styrax, as purchased, should be exposed in a thin layer to the sun for
several weeks. In this way much of its yellow colour is discharged, the
water it contains evaporates, and it becomes hard. It may then be
dissolved in chloroform, as already described. Instead of chloroform,
benzine, or a mixture of benzine and absolute alcohol may be employed
in making the solution, whilst a solution in ether will prove valuable
when rapid “ setting” of the medium is desired.
CLEANING AND Mountine PouycystIna.
The siliceous shells of these lovely organisms, the beauty of which is
only equalled by their variety, are found in profusion, and intermixed
with Diatomaceous valves, often of extreme beauty and rarity, in the
deposits (or so-called “earths”) of Barbados, the Bermudas and the
Nicobar Islands, whilst an entirely new and magnificent deposit was
discovered by the late Captain Perry, of Liverpool, at Jérémie, Haiti,
which contains not only a large number of novel species of Polycystina,
but many entirely new varieties of Diatoms.
The Polycystinous “‘ earth” should be broken into small pieces, about
the size of a nut, and boiled for half-an-hour to an hour, in a
strong solution of common “ washing soda ;” the disintegrated portions
being poured off into a large vessel containing clean water, from time to
time, and the boiling in soda repeated, as also the pouring off, until the
whole mass is perfectly broken up. When the disintegrated matter in
the large vessel shall have thoroughly settled down it should be subjected
to several washings, in order to remove the soda, the material being
allowed to settle thoroughly after each washing. It should then be
removed to a beaker or wide-mouthed bottle which should be filled up with
water, and after being thoroughly stirred or shaken up, the material should
i j
lvili. METHODS OF MICROSCOPICAL RESEARCH.
be allowed to settle for thirty seconds only, and the supernatant fluid and
its floating particles poured off into a large vessel; this process should
be repeated 3 or 4 times, and will give the heaviest density of sand and
Polycystina. Repeat this process with the matter in the large vessel,
allowing it to settle for two-and-a-half to three minutes, and the density
containing the small Polycystina will be obtained. Subject the remain-
ing matter to ike treatment, allowing it to settle in six inches of water
for 20 minutes, and the density consisting of the débris of Polycystina
and of Diatoms will result. Now boil each separate sediment in nitric acid
for fifteen to twenty minutes, remove all trace of acid by repeated wash-
ings, and finally boil each density in ‘a weak solution of Bi-carbonate of
Soda in a test-tube of large capacity for an hour; this will remove all
flocculent matter, and, after repeated washings, perfectly clean Poly-
cystina will be obtained. The heaviest density consisting of sand and
the largest Polycystina should be placed in a test-tube with about three
inches of water and subjected to rotatory motion, this will cause the
Polycystinous shells to rise above, and to free themselves from, the sand
and they can be poured off into a wide-mouthed bottle or beaker, the
sand being left at the bottom of the test-tube. This latter process should
be carefully conducted and repeated several times in order that no large
and perfect shells may be left amongst the sand. ach density should
then be bottled in distilled water. Polycystina may be mounted in
Balsam—in the same manner as Diatoms—or “dry.” Beautiful slides
can be produced by calcining the shells upon a piece of thick
platinum foil, or in a small platinum capsule, and mounting them
‘“‘opaque.” The neatest and best method of preparing -such
slides is to make a disc half an inch in diameter in the centre of a slip,
allowing it to harden for some days. A half-inch cover is then to be
cleaned and a sufficient quantity of Balsam, thinned with turpentine,
put upon it; the Polycystina are then to be placed in the Balsam in
sufficient quantity to form a surface over the cover when evenly spread
upon it ; the cover with the Polycystina is then to be put aside (as re-
commended with Diatoms) for 12 or 24 hours in order that the Balsam
may thoroughly permeate the forms and all air escape; the Balsam is
then to be hardened by gentle heat, as already described, and the cover
is to be laid upon a slip, with the Balsam upwards, and held over the
flame of a Bunsen burner until the Balsam is liquified ; the Polycystina
are then to be evenly spread upon the cover by means of a needle ; when
the Balsam is cold a small drop of Benzole-Balsam is to be placed upon
its surface and a clean half-inch cover to be warmed and carefully
lowered upon the Balsam. The Polycystina will thus be mounted
between two covers; now, turn the “mount” over, so that the under
surface of the lower cover shall be upwards, and coat this with Asphalt,
put the mount aside for a day or two, in order to allow the asphalt to
become thoroughly hard, then put upon the asphalt disc on the slip a
small drop of (cold) ‘‘ French Liquid Glue,” place upon this the asphalted
1This is to be obtained from any chemist, and is a most admirable, reliable, and
cleanly cement.
ON MOUNTING, lix.
under surface of the “mount,” and when the glue is quite dry finish off
the slide with either asphalt or white zinc cement.
THE PREPARATION AND Movuntine or InNszEcTs.
There are several processes for preparing and mounting insects, each of
which possesses special advantages, in respect of the results and appear-
ances it may be desired to obtain. Whenever it is possible, and except for
special purposes, and in dissections Insects should be mounted “ without
pressure,” since the flattening them out under pressure results in dis-
tortions, displacement of the parts and organs, and unnatural, and there-
fore, false appearances. It is, however, impossible to mount all insects,
or their parts, without pressure, and the following process will give good
results :— )
Place the insect in pure Liq. Potass: mixed with 4th ammonia fort.
The insect must not be allowed to remain too long in this solution, and
must be tested from time to time by placing it in water and pressing the
thorax. When the thorax is soft and the legs flaccid immerse the insect
in water for from 15 to 24 hours, then soak it in glacial acetic acid and
glycerine (half and half) for some hours.’ Again, immerse it in water for
from 12 to 24 hours ; it is now ready to be laid out upon the slip ; having
done this, preserving the natural position of the parts as closely as
possible, place a cover over the insect and tie lightly round it with soft
cotton, stand the slip on end to drain, plunge the slip into a turpentine
bath and leave it until all moisture has been driven out and the insect is
thoroughly permeated by the turpentine, drain off the turpentine, apply
blotting paper to remove any excess of turpentine from under the cover,
and run in “Benzole-Balsam” by capillary attraction. The cover
should never be lifted or allowed to shift its position after the insect has
been laid out.
When it is desired to preserve the brilliant or delicate colours of an
insect it should be placed, immediately after being killed by means of
Chloroform, in Liq. Potass, without any mixture of Ammonia, for from
two or three days, then soaked in water for 24 hours, then placed in
water, with 10 drops of muriatic acid to each ounce of water, for 24
hours, it should then be laid out and immersed in turpentine and treated
as already described.
In order to mount insects, or their parts, ‘‘ without pressure,” it is
generally necessary to adopt only the following simple process :—Soak
the insect for two days in equal parts of ordinary alcohol and water, after
which transfer it to absolute alcohol for two days, immerse it in turpentine
until it is not only completely permeated therewith and all air removed
but let it remain until it is sufficiently bleached or decolorised—in other
words, rendered transparent—and in order to ensure this result it should be
placed in a strong light. Select a cell, of the requisite depth, of pure
tin or vuleanite, which affix to the centre of a slip with the French
_ ——
1{nsects removed from Liq. Potass, after being soaked in water for 24 hours,
should be kept in strong, or glacial, acetic acid and glycerine (half and half) until
required for mounting.
ix METHODS OF MICROSCOPICAL RESEARCH.
Liquid Glue ; when this is dry, having cleaned the interior of the cell,
place within it the insect, and fill the cell with fairly thick Balsam until
it presents a slightly convex surface above the cell, lay it aside, as
previously recommended, under cover for twelve to twenty-four hours so
that all air may escape, put a minute drop of fresh Balsam upon the sur-
face of the Balsam which fills the cell, and carefully place a cover, slightly
warmed, upon it, close the cell by gentle and equable pressure, at once
remove, by means of a soft brush and benzole, all Balsam which has
exuded under the pressure, let the mount harden for a day or two, and
then apply white zinc, cement or asphalte.
Cells are to be obtained of various sizes, having pure tin caps to fit
exactly over them, after the cover is applied, and these not only impart
great strength and security to the cell, but ensure the neatest possible
finish to the mount. Mr. F. Enock, whose exquisite entomological pre-
parations are altogether unrivalled, is to be credited with this admirable
device, as well as with various other improvements in the special branch.
of the art, to which he has devoted himself with such singular success.
Tut PREPARATION OF VEGETABLE SECTIONS.
Whensoever possible stems, leaves, roots, petioles and wood should be
cut fresh and sectionised as soon as may be—all such specimens should
be kept in a mixture of equal volumes of alcohol, glycerine, and water.
Sections also may be stored in this mixture. Nearly all vegetable sec-
tions require bleaching before being stained ; very delicate tissues may be
bleached by means of alcohol—hard and deeply-coloured stems and woods
must be bleached in a liquid thus prepared :—
To one pint of water add 2oz. of fresh chloride of lime; shake this up
thoroughly two or three times, and allow it to stand until the lime shall
have settled. Make a saturated solution of common ‘ washing soda.”
Pour off the supernatant fluid from the chloride of lime, and, by degrees,
add to it the soda solution, until all precipitation ceases. Filter the
solution, and keep it in a stoppered bottle, in the dark. No fixed time
can be given for the bleaching process, the colour and density of tissues
being so variable. Experience, however, will be rapidly gained, and
over-bleaching easily avoided. The sections being bleached, must now
be washed in distilled water, several times changed, and
allowed to remain for twenty-four hours in the final water,
to which add 8 or 10 drops of nitric acid to each half-pint. Transfer the
sections to alcohol, for an hour before staining them. To bring out details
of structure and to display cell walls, &c., there is no better stain than
Logwood, and for singly stained vegetable sections it is to be reeommended
in preference to all other staining fluids. The following process will give
admirable results :—
lst. Remove the sectionfromalcchol to water for a few minutes.
2nd. To 3 per cent. alum solution for 10 minutes.
3rd. Stain in aqueous logwood stain. (See page xlii.)
4th. Place in alum water to remove stain from surfaces,
5th. Wash thoroughly in water.
ON MOUNTING. }xi,
6th. Place in alcohol for two or more hours. Float the section
lightly on the surface of oil of cloves: when it sinks it is ready to be
mounted in Balsam.
To DousLE STAIN VEGETABLE SECTIONS.
Ist. Place the section in an alcoholic solution of Iodine Green
(3 grains to the loz. of alcohol) for one or two hours.
2nd. Soak it in alcohol for ten minutes.
3rd. Remove it to water for one minute.
4th. Immerse it for two hours in Carmine fluid, made as follows :—
Carmine, 15 grains; Ammonia, 15 grains; Water, 20z. Dissolve the
carmine in the ammonia by means of gentle heat, add the water, and
filter.
5th. Wash thoroughly in water.
6th. Place in alcohol for ten minutes.
7th. Float upon oil of cloves and mount as previously described.
Mr. Gilburt, whose vegetable preparations are most successful, recom-
mends the following double-staining fluid, in which the sections are
immersed, and which produces perfect differentiation. Dissolve of
Magenta Crystals 4 grain in 1 ounce of alcohol, and of Nicholson’s soluble
blue 1 grain in 1 ounce of alcohol; add to this 4 drops of nitric acid.
Filter both solutions.
To 2 parts of the blue add 7 parts of the magenta solution. Immerse
the section for from 1 to 2 minutes, remove it to absolute alcohol, thence
to Benzole (to fix the magenta); thence to oil of cloves, and mount in
Balsam.
Picro CarMINE, DovuBLE StTarininc.—FPicro Carmine as a selective
double’ stain cannot be surpassed. The process is as follows: Take of
carmine 2 grains, liquor ammonia 4 drachm, distilled water 1 ounce ; dis-
solve the carmine in the ammonia by meaus of gentle heat, add the water.
Dissolve 8 grains of picric acid in 1 ounce of alcohol, also by means of
gentle heat, and mix the two solutions.
Place the sections in alcohol for one hour—immerse them in the
recently filtered staining solution for from half an hour to three hours—
i.e, until they are sutticiently stained,—wash them in alcohol, immerse
them in an alcoholic solution of Picrate of ammonia for one hour, and
for a second hour in a like solution, in other words, change the solution
once during the two hours. Place them in alcohol for a few minutes, and in
oil of cloves as already described, and mount in Balsam.
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ON MICROSCOPICAL DRAWING AND PAINTING.
A great teacher has said ‘‘ Drawing should be considered not an accom.
plishment, but a necessity. Learning to draw is learning the grammar of
a language. Anybody can learn the grammar, but whether you have any
thing to say is another matter.” To the naturalist this accomplishment is
of great importance ; accurate illustration adds to the value of written
description. At every point the microscopist is sensible of its deeper sig-
nificance. Such a control quickens the perception, excites exact observa-
tion, and creates an interest beyond research, admiration, or curiosity.
The compactness of the vision, presented by the microscope, so rivets the
attention, that changes, disclosures, development of activities, in organisms
often lost and swept away, after cursory examination, rouse in a zealous
observer an impatient desire to possesss some power, beyond words, to
place on paper a memorandum or record, however rough, of things rarely
discovered under the same conditions. This ability is a result of practice.
There is no royal road but that traversed by enthusiasm and earnestness.
Sketches from the hands of a dexterous microscopist, marking first impres-
sions, are often more valuable and superior than the formal work of the
mere draughtsman, who may not even know the significance of the subject,
especially when the result is a replication of drawings made by the actual
observer. He necessarily falls into one or other of two errors; he
mends and improves, or obscures material points by drifting into formal
monotony ; a microscopical draughtsman must essentially be a microsco-
pist, and work direct from actual observation, completely understanding
the matter before him.
There are three well defined characteristics of microscopical representa-
tions, drawings of tissues, or minute organisms, requiring for elucidation
high powers, delicate conditions of light, conducted under careful obser-
vation and technical skill, satisfying the highest biological research, in its
progress demanding rigorous precision ; then, rapid sketching, catching
features, graphic memoranda ; without hesitation, or the assistance of the
camera-lucida jotting down, and washing in, with tints, unexpected
appearances, this readiness should be cultivated by those desirous of
adding record to observation; many most important phases in the
sequence of activities have been seen and passed over, when a few rough
lines would have induced and helped further research, but beyond this
tentative work, and the stern formality of scientific requirement, is a
finished “picture ;”-at this crucial point the capability of the microscopist
Ixiv. METHODS OF MICROSCOPICAL RESEARCH.
and artist blend, involving knowledge of the subject, the arrange-
ment of optical apparatus, judgment, and study in the methods
of procedure. A drawing may be true in its scientific aspect,
and possess artistic features of decided interest—the one may
incorporate the other. The illustrations of Mr. Gosse’s books are
instances of this peculiar quality. ‘Still Life” has arrested the atten-
tion of artists, of all time, from Missal Illuminators to Royal Aca-
demicians, such results have no scientific import, but like all art pro-
ducts, awaken gratification in: appreciating the power applied in pro-
ducing their essence, and, without degrading the legitimate functions of
the microscope, it is possible to extract from its revelations, models of
exceptional charm and excellence, associated, »moreover, with scientific
value. Although the bias of an expert microscopist and practised
artist may not often touch the same mind, it is certain that when a keen
perception is directed to complications of beauty, with rare conditions of
light, and effulgence of colour, the instrument becomes the very touch-
stone of artistic feeling, and, beyond mere beauty (which, in visible
nature, is inexhaustible) there are revelations of structural form, quaint
elegancies, mysterious changes of tissues, and embryological develop-
ments, under radiances, hidden, not only from ordinary familiarity,
but even from the cognisance of many who have not had the opportunity
of exhausting the resources of a fine instrument, with -all its accessories.
[t may be urged that few have the ability to approach art of this descrip-
tion, but the power of drawing, quickly develops itself, especially when
stimulated by special and eager interest, concentrated on special objects;
no one led by inclination to “contemplate what’ may be seen under such
circumstances, can be destitute of an appreciation of art in its most ex-
alted sense. The education of the eye (the basis of esthetic culture) as
exercised by the fascination and mental excitement of microscopical re-
search, progresses in a degree hardly yet understood, or appreciated ;
every student has within his mastery this power; the manipulation of
the instrument, the means of display, the use of materials, are matters
of expertness, and are extensively self-taught, possibly some instruction
may do more than groping alone, but in the end experience is the best
master. It is proposed in this essay to detail such an actual experience
in words, directed more to mental judgment than technical education.
A microscopical drawing may be absolutely true, and an artistic grace
secured, by preserving line for line what is actually presented, assuming
the preparation to be fairly perfect, in other words, not drifting into a
stilted diagrammatic style, or wandering from close observation, because
the subject appears to have a certain regularity ; no two cells, vessels, or
fibres are absolutely alike ; to give ‘‘ life”. to a picture, every part of the
structure should be a portrait, ‘the pencil deviating from accuracy melts
into falsity and confusion, wnifor mity ts fatal, and obscures important
differentiation of. parts ; again, In order to’ delineate what is expected, or
wished to be seen, aiming ‘ab correction,” is to. be avoided; it is better
to draw imperfections, if they be. present, an overlapping or torn struc-
ture often reveals an important fact, so-patent is this, that a ‘‘ fabricated ”
ON MICROSCOPICAL: ART. lxv.
drawing may be detected in a moment, especially of Diatomaceous or
Infusorial forms—a broken fragment, a solitary individual is the clue to
a perfect whole, or group; such built up arrangements have no charm
beyond technicality. A good representation possesses a mingled quality
of accuracy and imperfection, a paradox, which stamps its value! Sup-
pose a preparation of vertical section of human scalp of rare excellence,
double stained, disclosing beauty in many perfect hairs traceable in their
course direct from the base of the bulb, embedded in the follicle, and
emerging from the cuticle above. In cutting a section of such
delicacy it would be impossible to avoid slicing through a hair or two
diagonally, thus leaving the tops of some, the ends of others; this result
or defect, is a feature of significant interest from an art point, faithfully
copied it gives life and character. In a diagram, the imperfection, by
comparison with perfect hairs, might be remedied, the mutilated parts
‘‘restored ;” but such an interference destroys at once the graphic quality
of the picture, adding nothing to its scientific interest. Absolute
accuracy in depicting what is presented may, however, in some cases, be
qualified, and truth evolved by a knowledge of the structure as it should
appear, particularly in cellular tissues, in close contact. In such cases
the artist ought to be cognisant of elementary forms, as arranged under
contiguous pressures, and the position of spherical, oblong, or cubical
elastic cells, as affected by juxtaposition in, over, or under spreading
layers. Coupled with the perspective of such conditions, this facilitates
progress. In opaque subjects, under binocular vision, where the rotundity
of a reticulated surface fades in dimensions, and shadow, in different lines,
this abstract knowledge is important, and should be acquired, as many
objects could not be effectively represented without its study—always
keeping to general appearances; it is an ability which removes difficulty
in unravelling the disposition of parts, especially under high powers ;
when sections are cut either too thin, slightly oblique, or disrupted by
the knife, the mechanical interferences of parts when understood, may
be restored. The functions of an artist, cognisant of a condition of
antecedents may be fairly exercised in the progress of a drawing, but it
must never trench upon absolute truth and discrimination in treatment—
-a drawing may be ruined in a moment by a false line involving impossi-
bility of structure ; toa critical eye, this is fatal. In fine work, dealing
with malpositions, shrinkage of tissues, disseverances and pseudo-appear-
ances—inevitable even in the finest preparations—the utmost judgment
is required.
The effect of a microscopical drawing is enhanced by its inclusion in
a circle—surrounded by a black margin—forming a square. The size of
the circle is important—it may be too large, or too small; experiment
proves that a space three inches and three-quarters in diameter approxi-
mates nearest to the impression made on the mind, of a “field” as
seen with a B eye-piece, this circle may encompass magnifications under
any power. A metal plate four inches and three-quarters square, with
an opening of the dimensions given, should be procured, this ascertained
gauge will soon prove a necessity—placed ona drawing block, a pencil
Ixvi. METHODS OF MICROSCOPICAL RESEARCH.
swept round the circle and outside the square gives the interior for the
drawing and the lines for backing with Indian ink—these discs should
be prepared before the work is commenced, and the importance of this
arrangement will be shown hereafter.
The help derived from the camera-lucida is strictly limited, it cannot
be employed beyond a certain point, no elaboration can be effected by its
prolonged use, it should be discarded the moment its legitimate purpose
of marking points and positions is achieved ; those experienced in its
employment always feel a sensible physical relief, and “ breathe again ”
when it is set aside to settle down to the earnest work of direct vision ;
its application to the instrument is sufficiently familiar, the micro-
scope rendered monocular by withdrawing the prism, the camera-
lucida is slipped over the A eye-piece—which should always be
used (higher eye-pieces expand the field beyond the fair range of the
instrument), clamping the object, the microscope is depressed into a
true horizontal position (if not, a distorted picture would be the result)
and the lights adjusted, the distance from the object to the eye-piece
should be nearly equivalent (if anything a little more), to the reach from
the eye-piece to the paper. With a microscope standing ten or twelve
inches high (a Ross No. 1) this condition would reveal the phantom
of the object, outside or about filling a circle of the dimensions given on
the drawing block, if any difference of over, or within, lapping appear,
it may be remedied by raising or otherwise adjusting either the paper or
the microscope so as to obtain a perfect coincidence of the vision and the
circle, the importance of a measured disc is now manifest, proportion is
affected by distance from the eye-piece, and with this gauge and a stage
micrometer, adrawing may be kept to measurable bounds; difficulties
have existed as to amplifications expanded by the cumera-lucida, absolute
accuracy may be ascertained by the use of micrometers as far as the eye-
piece is concerned, but the known diameter of a circle on which the
image is projected, is an easy factor in such calculations, beyond this, the
circle is mechanically useful, if the block should slip when using the
camera-lucida, there is an ascertained line for re-adjustment. The light
_ on the paper should be in excess of that from the object ; speed and pre-
cision are essential, quickly make recognised points and lines, never
attempt to draw detail, nothing fatigues the eye or distracts the mind
more than the prolonged employment of the camera-lucida. No advance
can be made by its continued use, any attempt at elaborate work ends in
confusion. Cultivate the “knack” of seeing at the same time, and in
the same position, the reflections and the image of the tracing point (the
hardest pencil, sharply cut); it is not necessary to strain the sight to
keep the entzre field always in view, there is a condition of steady
gazing, the eye not too close to the prism, when parts of the object
can be taken separately, but this is a result of the facile use of the instru-
ment. The neutral tint glass or any form of reflector, giving only one,
and, consequently, a reversed image, is useless, for afterwards continuing a
drawing from direct vision, but with any description of camera-lucida, —
the pencil, once placed on the paper, should not, if possible, be lifted
ON MICROSCOPICAL ART. Ixvii.
until all determining lines are fixed ; the eye (unsteady at the best) and
the pencil point must be in unison. Keeping the pencil on the paper
preserves “the place.”
In arranging any object for drawing, it should be sufficiently magnified
to shew everything bearing upon its elucidation, and, as a rule, an isolated
subject, a complete form, ought to occupy, as nearly as possible, the
entire field. Some specimens necessarily overflow the circle—surfaces
of injected preparations, botanical sections exhibiting features requiring
the highest magnification, consistent with the preservation of a focal
plane, which, obviously, cannot be fairly disclosed (except at a loss of im-
portant detail), are beyond the scope of the circle of popular survey. It
must then be abandoned, the drawing spread out, and made in sections
by shifting, and combining visions. Using the camera-lucida any part
may be carefully drawn, making two or three (if angular, the
better) prominent points, corresponding with similar appear-
ances in the subject. These marks or tri-angulations (as
near the margin of the field as possible), must be remem-
bered, the position of the object is then moved by stage adjust
ments, and another part of the field arranged, the included marked points
are coincided, by shifting the block or paper, and further outlines ex-
panded, in this way the camera-lucida may be used under high powers
with four or even six combinations of vision—and the parts, with care,
will ‘‘read into” each other, and result in a drawing of considerable
dimensions, perfectly mapped, and true in contour, it may then be con-
tinued part by part.
After faint outlines and points of certainty are securely indicated, the
microscope is placed in position, and with B eye-pieces drawing from
direct observation commenced ; prolonged work is facilitated by removing
the caps of the eye-pieces ; when attentionis continually diverted from
the instrument to the pencil the fatigue is lessened by keeping the eyes
some distance from the glasses, cultivating a faculty of losing the recog-
nition of the entire objects, only directing the alertness of vision to the
particular part under consideration, in fact itis not necessary, nor, is it
prudent to strain the sight to keep the full blazon of the field under
observation, and this rule may, with advantage, be applied to the general
use of the microscope. At this point, steady work commences, faint
camera indications are studied, lines corrected and strengthened, either
with pencil, or better, a fine sable brush or pen, carrying a mere tint of
Indian ink or ‘‘ Payne’s Grey.” Extreme care is necessary ; no mistake
of line can be permitted ; paper, intended for such drawing, and delicate
after colouring, does not permit erasure, or the contact of any rubbing
out substance; and consistent with the subject, too much fine line
cannot be put into the work ; no attempt at shading, either with pen or
pencil, must be attempted. The lines being perfected, and the subject,
as it were, “modelled,” the painting may now be cautiously commenced.
The absorbent quality of paper (well known to those accustomed to
water-colour sketching), interferes with, and sometimes helps, artistic
lxviil. METHODS OF MICROSCOPICAL RESEARCH
results ; without entering into the rationale, but bearing upon the point,
it may be mentioned that no wash or even line should be superimposed
or carried over another until the first be perfectly dry ; stippling should
show a granulated appearance, lost when touches are allowed to run into
and become absorbed by each other.
Illumination, and its diversities, for art work, are of as much import-
ance as the amplification. Power and light should be adapted to each
other, and to the character of the subject, its mode of preparation, and
what it is expected to reveal. The light, whether from gas (argand
burner), or oil, should be capable (in the case of gas, by means of flexible
tubing), of being placed in every possible position, from the surface of
the table, to, or even above the level of the stage. Ordinary transparent
objects, under low powers, are sufficiently shown with transmitted light
from the mirror, modified through a diaphragm of waxed tissue paper,
ordinary preparations of insects cannot be better displayed ; the best
reflected light is from the side speculum, collected from a flame through
an intervening plano-convex lens, on a separate stand. In all observa-
tions, even the simplest, accuracy of light-focus (often neglected) is
important. For powers beyond the half-inch, transmitted light is
aided and improved by the purity and control afforded by the
achromatic condenser, an instruament in the hands of novices,
not always well managed, or sufficiently appreciated ; focussing on the
same plane as the object, the source of light; it is capable of regulating
intensity, purity, and deviation of rays—by apertures and stops, with
which it is supplied, and thus the most varied combinations may be
secured. Its use should be thoroughly mastere|; as it produces the
most beautiful, instructive, and even amusing effects. For instance,
with a half-inch objective and full aperture, carefully focus, on
a ground glass slip, the flame of the lamp, now interpose a dark
stop, which should occupy, in the centre, about one-third
of the field ; removing the slip, replace it with a group
of (say) volvox-globator ; the plants will be seen rolling from the outer
ring of pure transmitted light, into the central black disc, where they:
appear like emeralds ; free-swimming rotifers will.pass backward and ~
forward, from the outer ring of parallel rays, into the eclipse of the dark
stop, where they become by oblique radiations, self-luminous; no finer
example, as showing in one field, at the same moment, two extremes of
illumination, could be placed before the microscopical artist, or an
ordinary observer to prove what may be effected by an adept in the use
of this beautiful instrument. With low powers striking presentations of
artistic illumination are under easy control; in particular, the use of the
paraboloid combined with light from above. An experienced microscopist
is familiar with all these methods—but the artist, alert and eager for
experimental conditions, often hits upon effects not generally applied,
possibly sacrificing scientific truth to esthetic desire ; a result of positions,
and foci of illuminators—their accurate or eccentric adjustment, cutting
oft central or peripheral rays, dispersing or half obscuring light
by intervening transparencies, The importance of such combinations ig
ON MICROSCOPICAL ART. lxix.
paramount in the examination of semi-opaque objects immersed in a
thick bed of medium, without pressure. These preparations are in
parts dense, even solid, combined with tissues of extreme delicacy and
transparency ; nothing being crushed, they shew the impossibility of
revealing the correlation, or association of parts, by mere transmitted
light—or in any way, except (may it be said) by artistic discernment.
The head, and surrounding parts of an insect, prepared in this
way, with pure light from beneath and above, discloses a combination
of form, and colour, of surpassing beauty, the blaze from the speculum
sweeps over the opaque parts with reflections revealing the most exquisite
tints, while the paraboloid shows, in actual perspective, the parts beneath
in all their natural colour, and bathed in refulgence. An opaque polypo-
dom, touched by such reflections, while the extended polyps are illumin-
ated from below, is another instance, amongst many, of beauty, exalted by
light. 7
For purely opaque objects, the only good light is from the speculum,
by no other means can the finest effects of colour and shadow be obtained.
It should be fitted to the stand of the instrument, not to the stage, nor
should it slip on the front of the objective. On the stand it can be moved
without disturbing the object or the focus. The old fashioned Lieburkuhn
cannot be used ; it requires an object to be prepared in a particular way,
and, as an illuminator is palpably defective, the light completely surrounds
and enwraps the object ; brilliancy is present, but no contrasts. In using
reflectors, the lamp should be placed close to the level of the stage,
within easy reach of condenser and speculum.
In painting purely opaque objects under top light the treatment of
background deserves attention, eggs of insects or parasites, are generally
attached to fragments of wood, leaves, cuticles, hairs or feathers—it en-
hances the effect, and beauty of a representation—if such details are care-
fully painted, and the rest of the field delicately stippled up with Indian
ink, to the edge of the circle. This applies to many subjects—threads of
alow, or vegetable stems supporting such objects, as fixed rotifera, polyzoa,
ete., introduced into a drawing, add greatly to the interest and make
most attractive pictures. Any prepared mount or specimen should be
as perfect as possible, and considerable experience is necessary in order to
decide, what is fairly good as a preparation, and worth drawing.
Common objects of easy procurement from the woods, the
garden, and the stream, are exquisite models for the draughtsman,
their excellence, interest, and freshness are necessarily superior to even
the admirable results now obtained by professional preparers, aided by
mechanical appliances, and rare skill in the use of re-agents and staining
fluids.
In illustration of illumination ofa precise object, as affected not only in appear-
ance, but in colour, reference may be made to the plate, which represents a trans-
verse section of a spine of Echinus under four diverse conditions, the upper division
(1) with fairly good transmitted lights, and (2) improved by a condenser, the
lower portion (1) under ordinary reflected light, and (2) aided by a paraboloid or
spot-lens,
iexe METHODS OF MICROSCOPICAL RESEARCH.
It is obvious that objects under polarised light, are practically beyond
the power of faithful delineation, in all painting, whether in local tint or
shadow—purity of colour and the preservation of brilliancy—is of the
first importance ; In order to render, beyond a mere semblance, any subject
under the polariscope, it would be necessary, if such a power were possible,
to dip the pencil into light itself, and an insuperable difficulty exists in
the permanent preservation of the adjustments necessary for future
work, the slightest touch, or alteration of any part of the instruments ;
and even an obscure change, beyond all control, in the quality of the
source of light alters the entire gamut and consonanee of colour, impossi-
ble to re-establish, yet, if selenite films be dispensed with, some results
nay, with care, be recorded ; petrological preparations, the dichroism of
crystals, sections of shell, bone, scales, horn, and other semi-transparent
organic structures, of varying densities, reveal points of interest only seen
under such conditions and may be noted ; but considering that the most
exalted light at the command of the artist, is the white of the paper,
(in all cases, to be jealously preserved), and that the polariscope dis-
closes the purest coloured lights, associated with complimentary tones of
every gradation, itis clear how futile are the resources of the palette to
depict the lustres and unisons of tones as revealed by this fascinating
instrument.
Structure and its thoughtful exposition is the limitof draughtsmanship,
and it is here that the photographic lens as a delineator fails, thesuperiority
of work produced by a hand guided by cultivated observation as compared
with a photographis the operationof amind capable of expressing combined
and superimposed tissues, in having at command a control and adjust-
ment of various planes of surfaces, and without militating against
scientific truth, seeking for, and obtaining even picturesque effects, this
important power is felt when searching the depths of an opaque injection,
or peering into intricacies of tissues. The objective used in micro-
photography, especially if it be a high power (unlike the penetrating
quality of an ordinary portrait lens), is strictly limited to one, and that
a very delicate focal plane requiring a fine and Fina adjustment, en-
hanced by the difficulty that the visual and chemical foci of microscopic
objectives do not coincide, entailing a manipulation which never touches
perfect precision; on the other hand, a draughtsman may arrange a
-minute and just perspective of parts, absent in a photograph, anticipating
the presence of relative parts, and having at command the fine adjust-
ment, he can feel his way, conscious that at the slightest touch a fresh
point, perhaps an important revelation, flashes into sight, supplying a
link to the better understanding of the whole. A drawing, produced
under thoughtful guidance, conveys to an appreciative observer an attrac-
In the establishment ofa ‘‘ cabinet” nothing should be admitted, that is pro-
curable, fresh and living, at each recurring season. A ‘‘collection” should be
strictly limited to typical subjects difficult to procure and requiring special treat-
ment, involving section cutting, injection, dissection, or methods of preservation
and revelation, necessary for future study and reference, this would exclude from 4
cabinet (instances need not be particularised) much, which even degrades it,
ON MICROSCOPIGAL AR’. Ixxi.
tion totally absent in a photograph ; the latter may possess the important
and essential element of proportion and freedom from exaggeration, but
exactitude is never absent from a drawing disclosing understanding, and
conscientious treatment.
There may seem little or no analogy between landscape and micro-
scopical painting, but the same principles are involved—points of sight,
effective light, general entourage—possibly a ‘‘ preparation,” dealing
with unusual and unexpected complications of line, embracing physio-
logical difficulties, requiring delicate conditions of luminosity, demands a
deeper judgment, for it is often necessary to prepare the mind by careful
and prolonged study, before the paper is touched ; especially in con-.,
sidering and anticipating difficulties of representation, and how they may
be overcome—delicate structures, under the most careful illumination,
often appear as streaks of LigHT, when a slight touch of the condenser
may reveal distinct lines. These are points to be studied;
in fact, the subject should be “gone over” and arranged in all
particulars, so that it may not outstrip the power of the pencil.
All materials should be of the finest quality, the paper, bard, thin,
smooth, and unglazed—delicate pencil drawings may be made on Bristol
board, but such or any glazed or hot-pressed surfaces, are totally unfitted
to take colour. Fine drawing paper is preferable, when blocks are used
each surface must be examined for imperfections with a hand lens; a
delicate painting may be ruined, at a critical point, by an imbedded hair,
an abrasion, or minute speck ; in the manufacture of these blocks, it has
- been found that in cutting up and folding the paper the true surface is
not in every piece placed uppermost. For important work it is safer to
select sheets strained in the usual way, in a small-sized folding drawing
frame. Paper improves by age. If of undoubted antiquity, it fetches
high prices. It is impossible to render satisfactorily, on a white surface,
opaque preparations showing minute injected anastomosing veins, arteries,
or glands, the dark interstices separating them, cannot be drawn, or picked
out, without sacrificing the regularity or destroying the uniform diameter
of the vessels—but such subjects may be effectively painted on a dull black
paper, which may be previously pasted on a drawing block under pressure,
using opaque or body colour, vermillion, yellow ochre, Antwerp blue,
and carmine, combined with and regulated for substance, and tint, with
zinc white and gum water. Payne’s grey, with zinc white, produces the
peculiar shadowy hyaline tone so often seen as a substratum in such
preparations where semi-transparent spongy tissues are involved—fine
effects of receding distances—in following the depths of structures, may
be produced by its use. Numerous brushes of sable are required, the
hairs short and coming to a fine point, they should be of the best make,
no brush that has touched Indian ink can be used for delicate colour, and
those employed for carmine, yellow, and blue, should be marked and
kept distinct, the same applies to pens, often required, but the pen carry-
ing colours must be used with extreme discretion. If a fine line can be
obtained with the sable, it is of higher quality, moreover with the handy
pen, the temptation is great to obtain hurried results by strokes and
Ixxil. METHODS ‘OF MICROSCOPICAL RESEARCH.
dots, but for pure black and white memoranda, or representations requir-
ing speed, nothing can equal a fine pen, charged with Indian ink, or
neutral tint, remembering never to approximate, or cross a line,
until it be properly dry; with this precaution a pen draw-
ing may approach the semblance of an etching. The colours
should be dry cakes, the palette preserved as pure as possible ;
moist pigments, rubbed from pans, become contaminated, and
even dry cakes should be kept separated; loose and in contact they
chip and soil each other. Quality is all important, use only those which -
are ‘‘transparent.” Manuals on painting contain lists of recommended
pigments, and their qualities, generally meeting no attention ; for the work
in question, 1t may remove difficulties, to remember that important colours
are neutral tint, Payne’s grey, Antwerp blue, carmine, scarlet lake, yellow
ochre, Hooker’s greens Nos. land 2, and raw Sienna—colours to avoid, ver-
million, cadmium, the umbers, Emerald green, and “Vandyke: brown.
These are densely opaque, and ‘load” too heavily for delicate work ; a
good test is to rub a portion of each cake of a well-furnished box on a
clean porcelain palette, side by side. When dry, those which appear
dull and dusty (however useful they may be in landscape in large thin -
washes), reject: everything may be accomplished with the remainder.
There is nodifficulty in conductinga painting by artificial lightwhen conver-
sant with the character and combinations of the few colours really required,
a precaution, however, is necessary in painting tissues stained artificially
with logwood or analine dyes; these colours are very deceptive, and
differ in appearance under degrees and qualities of light. LLogwood
stain (often used) in daylight has a blue tinge, under the lamp it appears
as a decided port wine tint, and a difficulty may, (in fact, does) ensue in
matching day, and lamplight work. When the entire subject has to be
painted in the same tone, cakes of ‘‘ Mauve” and ‘‘analine blue” now
to be procured may be used alone, and thus stained tissues can be
painted under any conditions of light without leading into error. It
need hardly be said that such abnormal colours are to be used exclusively
for those special preparations, and should never enter into the composi-
tion, 07 even touch a general palette required for natural representations.
Indian ink must be of superlative quality, the difference in price, al-
though not deadly, is great. A piece should be secured, regardless of
cost, and treasured.
With practice in cultivating accuracy of touch, certainty of line, and
forgetting the existence of rubber and knife-edge, no difficulty may be
anticipated in drawing on wood, zinc, or lithographic stone.
Crouch End. dad bes i)
ON PHOTO-MICROGRAPHY.
It is too late in the day to claim any originality for the subject of this
chapter, since the application of photography to the delineation of micro-
scopic objects is almost as old as the photographic art itself, extending
back even to the days of Daguerrotype. Mlicroscopists of the present
generation should think of this, and while paying tribute to the patient
perseverance with which their forerunners must have worked under all
sorts of disadvantages, should blush that, notwithstanding all the recent
advances and all the simplicity of the gelatinu-bromide process, so few
avail themselves of the facilities it affords for the truthful and beautiful
delineation of the objects of their study. The chief reason for this neg-
lect is probably the idea among the uninitiated that photography is a very
complicated and difficult art,-dependent upon a very uncertain con-
dition in our climate—bright daylight—and that unless a person
had the necessary day-time leisure and were expert in ordinary photo-
graphy it would be useless to attempt this special application of the art.
It is to expose the fallacy of all this, and to show that any microscopist
armed with a small text book and with a simple apparatus which it is
quite within the bounds of possibility for him to make for himself, and
having no leisure time but the dark winter evenings, can, after a few
weeks’ practice, produce pictures of objects in his collection which'‘for
absolute fidelity, aye, and for beauty, are incomparably superior to the
highest flights of the draughtsman’s skill. In taking up the study of
photography a beginning must be made somewhere, and the tyro’s first
efforts may as usefully, and with as great a prospect of ultimate -
success, be directed to this branch as to any other. It is a matter,
not of doubt, but of certainty, that his first attempts will be failures,
from under-exposure, over-exposure, forgetting to draw the slide, and
therefore no exposure, fog, frills, stains, pinholes, under-development, and
other causes, but had he commenced with portraiture or landscapes he
would have had the same dismal record of good plates gone wrong,
and would have had the additional gratification of many an unproductive
tramp. Therefore we would say be not deterred from taking up the work
because you are not a photographer. Start operations and become one.
It will, of course, be impossible here to give any elementary instruction
in photography pure and simple. All that can be done is to describe
such apparatus and processes as are special to this particular work. For
all that is general a good text book of photography must be consulted!
1Captain Abney’s ‘‘Instruction in Photography,” Piper and Carter, is one
of the best.
lxxlv. METHODS OF MICROSCOPICAL RESEARCH.
The apparatus employed is simple. It consists of a microscope of
any ordinary construction, a powerful source of light, and a camera.
The mirror of the microscope is discarded except for special purposes,
because the loss by reflection is very serious. The microscope (see Fig.)
is placed horizontally ina line with the source of light, and with its
tube inserted by a light tight joint into the front of the camera, which
is supported at such a height that its centre coincides with the optic axis
of the microscope. The object is held on the vertical stage by means of
spring clips, and the light from the lamp is condensed on it by one or
more condensing lenses. There are two chief methods in use. In one
the eyepiece of the microscope is removed, and the inverted image is
received on the sensitive surface where it is first formed. In the other
the eyepiece is retained in its place, and the image first formed in its
interior is formed again with additional magnification by the aid of the
eye-lens. By the use of the eyepiece the advantage is gained
that any ordinary camera may be used, and in. consequence of the
shortness of the distance between the focussing screen and the micros-
cope, the various adjustments of the latter are accessible, while focussing,
without any special arrangements. In order to secure the same amount
of magnification or to cover the same sized plate, when the eyepiece is not
used, the camera must be of special construction so as to be capable of ex-
tension, to two or three times the former distance, and when so extended
to—say a yard—the focussing screen can only be reached.by rods and
bands or intermediate gearing. For facilty, therefore, the eyepiece method
is commendable, but the impairment of the image and the loss of light
due to the interposition of two additional uncorrrected lenses are so con-
siderable that we would advise the removal of the eyepiece for all but
special purposes, such as the covering of a very large plate.
The microscope may be of any ordinary construction that will allow
the body to be placed horizontally, and it should have a stop to prevent
it going beyond that position. It should be provided with a coarse
adjustment, by rack and pinion, and a fine adjustment for slow focussing.
Very much of the success of the work depends upon the excellence of
the slow motion. It is always a very important part of the microscope,
but for photo-micrography it becomes very much more so. It should be
free from the slightest lateral motion, lest, in focussing, the image be re-
moved from the centre of the plate, a very small displacement of the
object glass being sufficient to effect this, when working with high
powers and a long camera. It must work with equal smoothness
and sensitiveness, and without loss of time in either direction. If
the tube of the microscope can be shortened by unscrewing the part
above the fine adjustment so much the better, for when work-
ing without the eye-piece, a long tube, especially if it be a
narrow one, greatly contracts the field. This is one objection to the Jack-
son Lister form of stand for photographic work, and the difficulty here
can only be got over by selecting an instrument with a wide tube. There
is another objection to the retention of a long tube, whether the eyepiece
be employed or not. It is certain to give rise to a “flare” of light by re-
flection from its inner surface, and flare, whether arising from this source
PHOTO-MICROGRAPHY., Ixxv.
or from the setting of the object glass, or the interior of the camera it-
self, is absolutely fatal to the production of clean pictures, and results in
the diffusion of a uniform light all over the plate, which impairs the
- purity of the shadows and produces a general fog, One chief seat of
this internal inflexion is the fine adjustment tube. No amount of dead
blackening, or even lining with black velvet will completely stop it. The
only thing to be done is to interpose along the course of the tubes of the
microscope, and in the camera, and even the object glass itself if neces-
sary, a series of diaphragms. These may be cut out of visiting cards
with gun punches, and glued to narrow rings of cork to give them a grip
of the tube. They and the corks must be painted dead black with water
colour (lamp black), and theirnumber, position and apertureso adjusted that
a line drawn from the centre of the object glass to the edge of the tube
when at its shortest shall just graze the edges of all these apertures.
Thus arranged they will not contract the field, and will not allow a ray
of light to fall on anything but the front faces of the diaphragms them-
selves, whence it cannot be reflected to the plate. When the eye-piece
is used the diaphragms must be differently adjusted, for the tube then
practically ends at the front surface of the field glass, and its diameter is
practically the clear aperture of that lens,
Fearnley’s Kr
XXXVIli.
Rutherford’s, xxxiii.
William’s freezing, xxxv.
Microscope, The, v.
Microscopical Drawing and Painting,
bebe
Mounting, xlv. — The
Method. li.
Miiller’s fluid, xxi,
O
Osmic Acid Staining, xxii.
)
Photomicrography 1Ixxiii.
Picric Acid xxii.
Picrocarminate of Ammonia xlii.
Picrocarmine staining xliv., 1xi.
Polycystina—Cleaning 1vii.—Mount-
ing lviii,
* exposure
en eles Uae eg peters a ee Wakes. °K,
‘* ih hy an =, de Ree is 7
3 aah SEN is as a Ce
: =. Sage * IKE oye a ts
rit ts ie ee
wD be » ; \
gigi = A Preparation of Animal Tissues xvii.
Sala 3 », Botanical Specimens (to
Biche preserve) XXXiii. :
an a5 », Diatoms liii.
aoe bg , Insects lix. a
, . oe
Hit. ae ChOCystina ely,
Me Retina of Human Eye x.
‘* Ringing ” Slides Jii.
Rutherford’s Microtome xxxiii.
Ss
+ _—— Salt solution, xxiii.
pea peeeection cutting, xxxiil,
- -- Section lifters, x]viii.
toRCe Sections, Transference of, xlvi.
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Silver nitrate, xxv. ;
XXV.
Slides, xlv.
Staining, xliii.
Stains, ‘xiii. *
Styrax solutions for mounting Dis tO}
Ivii. ne ae
Sulph-indigotate of soda, xlii., ste
ing, Xliv.
y a
vee
Vegetable sections, preparation 9 of, | f, Is
staining, lxi. ade:
W
Water, xxiv.
White zine cement, 1. Sone
Williams’ freezing ‘microtome, xx3
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