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<U'-\,'V>\y<»-

THE PEACTITIONEE.

APRIL, 1889.

#rigmal Communkatbns.

ON THE FUNCTIONS OF THE GLOMERULI OF THE
KIDNEY: A CONTRIBUTION TO THE STUDY OF
ALBUMINURIA.!

BY J. 0. ADAMI, M.A., M.B. CANTAB., M.R.C.S.

Demonstrator of Pailiology in the University qf Cambridge.

The recent publication of a volume upon albuminuria by so
eminent a clinician as Professor Grainger Stewart,^ in which
the glomeruli of the kidney are considered as mere filters, and
the possibility that their epithelium may be of a secretory
nature is ignored, renders this a not inopportune occasion to
discuss the various theories of renal activity, especially with
reference to the part played by the glomeruli. I am the more
ready to accept this opportunity inasmuch as the works of the
two great authorities upon the glomerular functions — namely
those of Heidenhain ' and of Cohuheim '' — have not as yet
received an English translation, nor do I know of any extended

' A thesis for the degree of M.B. Cantab.

" Grainger Stewart, Lectures on Important Symptoms (II. Albuminuria).
Edinburgh, 188S.
' Heidenhain, Hermann's ITandbnch, vol. v., Leipzig, 1880.
* Cohnheim, Alhjcmcinc Pathologic, vol. ii. Second edition. " Berlin, 1882.

The PRACTiTioNEn.— Vol. xui. No. 4, B

242

ON THE FUNCTIONS OF THE

account in our language of their views upon the subject, or
rather of the arguments upon which those views are based.

The " mechanical " theory, based upon the excellent series of
researches of Ludwig and his school — Hermann, GoU, Over-
beck, and Ustimowitsch — has until recently influenced more
than any other the opinions of those who have worked upon
the kidney. The conception that the elimination of the urine
depends upon a single great factor, the blood-pressure, that the
whole of the urine is filtered through the glomeruli, and con-
centrated by diffusion through the cells lining the tuhuli
uriniferi, is one that can easily be grasped ; and for many years
this theory ruled alone, and was almost universally accepted.
Heidenhain,^ however, in 1874, reasoning by analogy, and ob-
serving that in its general nature the epithelium of the tubules
corresponds to that of the definitely glandular organs which
he had previously been studying, brought once more into the
foreground the older theory of Sir William (then Mr.) Bowman,
the theory that the watery elements of the urine are elimin-
ated by the glomeruli, the characteristic solids by the tubules.
And when, by injection of sodium sulphindigotate, he was able
to demonstrate the passage of substances through the cells
of the tubuH contorti, and to show that these cells, instead of
absorbing, excreted into the lumen of the tubules, the mechanical
theory broke down.^ But to the present day there are still
many who, like Grainger Stewart, consider the general blood-
pressure as the determining factor in the production of the fluid
part of the urine.

That blood-pressure plays a secondary r6le is however evident,
when the cases are studied in which, the general arterial
pressure remaining constant, there is an obstruction to the

^ Heidenhain, Arch. f. microscop. Aiiat. vol. x. p. 30 (187 1) ; Arch. f. d. gen.
Physiol, vol. ix. p. 1 (1876).

^ During the last few years Ribbert has revived the tlieory that the excess of
tirinary fluid is re-absorbed by the tubules. On extirpating the medullary sub-
stance of the rabbit's kidney he found that a more watery and profuse fluid passed
away from tlie remaining functional cortex. These results cannot however be held
to liave any value, for, as has been ])ointcd out, the kidney has a rich lymphatic
supply, and the fluid passing from the maimed organ must contain a proportion
of lymph probably very considerable, but not admitting of estimation. The
presence of this lymph invalidates any such conclusions as those that Ribbert has
sought to draw.

GLOMERULI OF THE KIDNEY.

243

outflow through the renal veins. Ludwig himself ^ appears to
have been the first to record the fact, since noted by numerous
observers, that narrowing or temporary complete closure of the
renal veins is accompanied by a rapid slowing or stoppage of
the urinary flow — by a diminution in the urinary excretion — in
spite of the undiminished general arterial pressure, accom-
panied as it is by an increased pressure in the glomerular
loops. This, Ludwig hell, was explicable on the assumption
that the dilated capillaries so pressed upon the tubules as to
constrict them, close their lumen, and prevent any passage ot
fluid through them. Heidenhain ^ has however combated this
view, pointing out that the alteration in the excretion of urine
is too immediate to be accounted for by sucli considerations,
and he has propounded the theory that it is the rate of flmo
through the glomeruli, rather than the blood-pressure, that
governs the passage of water from the kidney.

This theory, that the rate of flow controls the excretion of
urine, does not in any way imply that the blood-pressure is not
a factor in the process. Indeed, the rate of flow is itself deter-
mined by the blood-pressure, being the resultant of two opposing
forces :(1) the general blood-pressure, and (2) the resistance against
which the blood is forced through the kidney. The resistance
remaining the same, increased blood-pressure causes increased
rate of flow, and in such cases there is an increased formation of
urine. But if the resistance be increased and the blood-
pressure remain unaltered, or be not increased proportionately,
the rate of flow is diminished. These conditions are met with
in obstruction to the outflow from the kidney. The stoppage
of the urinary excretion cannot be due to diminished arterial
pressure in the renal capillaries, but may be explained by the
diminished velocity of the blood-current.

The more recent work of Paneth ^ has wholly confirmed and
established Heidenhain's contention. Paneth, placing round
tlio upper abdominal, or thoracic, inferior vena cava a fine
thread capable of being easily controlled, found that in every

' Ludwifj, Wiener Situiiffshcr. vol. xlviii. p. 275 (1863).

s Ilcitlcuhain, Nermann's Ifandb. rlcr PhysioJoijie, vol. v. p. 321. Ticipzi^, 1880.
■' Paneth, Ucher den. Kinjlms venoscr Stanniuj nii/die Mcii'jc dcs Hams, Arch./,
d. (les. Physiol, vol. xxxix. p. 515 (1886).

R 2

244

ON THE FUNCTIONS OF THE

case in which the constriction was suflBcient to produce any
obstructive efifect (with a weight, for instance, of 35 grammes or
under 1 ounce attached to the thread), the urinary excretion
became less, and this often where there was a simultaneous
increase in the aortic pressure. That the diminution was not
due to compression of the tubules he proved by injecting a
diuretic, sodium nitrate, along with chloral. When the flow
from the ureter had almost come to a standstill in consequence
of the continued constriction and obstruction of the inferior vena
cava, and of the partial venous stasis in the kidney, the diuretic
caused an immediate and copious excretion of urine, although
the effect of the chloral had been very markedly to lessen the
general arterial pressure, and although, as shown by Roy's on-
cometric observations,^ the tendency of the sodium nitrate would
be to cause a further expansion of the renal vessels.

Immanuel Munk, in his paper upon the extirpated kidney to
which I shall refer later, cites experiments to prove the same
law, namely that the rate of blood-flow and not simply the
blood-pressure determines the glomerular excretion. With a
constant pressure in the renal artery, he passed through the
organ, first simple deflbrinised blood, and then the same con-
taining a diuretic {e.g. urea). And he found that under the
influence of the latter there was a more rapid flow of blood
from the renal vein and of fluid from the ureter. But, as Pro-
fessor Heidenhain has pointed out to me, although the pressure
in the renal artery is unaltered, it by no means follows that the
blood-pressure in the glomeruli has not undergone an increase.
Dilatation of the renal arteries and of the vasa affercntia, by
reducing friction in these vessels, will cause the blood to enter
the glomeruli under higher pressure than previously. Munk,
therefore, has not with certainty eliminated the factor of
pressure. It would be interesting to see what results ensued
from this method if, instead of keeping the pressure in the
renal artery constant, it were lowered upon injection of the
diuretic.

Admitting, then, what is now very generally accepted by
physiologists, that it is the velocity of the flow through the
glomeruli, and not solely the blood-press'ue in them, that

* Hoy, Procccdiwjs of the. Cambridge Philosoph. Hoc. May 23, 1881.

i
i

GLOMERULI OF THE KIDNEY.

245

governs the excretion of the fluid of the urine, there remains
the question as to the nature of this excretion ; is it simply a
process of filtration, or is it more nearly allied to a process of
secretion ? *

This prohlem of the nature of the glomerular activity is of
special importance from a clinical stand-point, inasmuch as upon
its solution depends the interpretation of that most grave
symptom, albuminuria. Heidenhain,^ in his classical work upon
the Physiology of the Processes of Secretion, insisted on the se-
cretionary view, and Cohnheim ^ was of almost the same opinion.
But more recently Senator * has revived the theory that the
glomeruli act simply by transudation, Runeberg holds con-
sistently to the same view, and Grainger Stewart accepts
Senator's conclusions.

Senator's theory is briefly — that the fluid portion of the urine
is derived in part from the glomeruli by transudation, in part from
the epithelium of the tubules. He considers that just as other
glands in secreting any substance always excrete with this a
certain amount of watery fluid, so in the cells of the tubules the
like process occurs. And Grainger Stewart states ^ " at all events
we may hold with certainty that the water is mainly eliminated
by filtration through these structures (the Malpighian bodies).
But the urea and other urinary solids are not discharged by a

* Let me premise that hy& filtrate is understood the fluid which passes through
the larger meshes of a membrane under the influence of piessure ; such a fluid con-
tains proportions of all the soluble substances present in the mother-fluid. A t ...u-
datvm, according to the general employment of the term, is a filtrate from the bio id,
and so should contain the salts and albumens of blood-serum, the amount of fluid
transuding being directly dependent upon the blood-pressure ; while the com-
position of a secretion is such that it cannot be explained by the laws of filtration,
its quality being determined by the specific characteristics of the gland-cells. These
cells in the simplest cases have only a selective power, extracting certain substances
from the blood and excreting them. Where more highly differentiated, they have
in addition definite synthetic or metabolic powers. A membrane, which while
the blood-pressure remains constant at one time permits and at another prevents
the passage of fluid from the blood, cannot be looked upon as wholly dependent
upon the laws of filtration ; such a membrane evidently possesses specific pro-
perties, properties of too complex a nature to be accounted for by the laws that
govern a single and comparatively simple form of physical action.

^ Heidenhain, Hermann's Handbuch, vol. v. p. 336 (1880), and also Breslauer
drtzl. Zeitsehr. No. 22, 1879.

^ Cohnheim, Allgemcim Pathologic, vol. ii. p. 319 (1882).
, * Senator, Die Albumimiric. Berlin, 1882.

" Grainger Stewart, loc, cit. p. 60.

246

ON THE FUNCTIONS OF THE

filtration, but by a secretive process performed by the cells of
the tubules. Along with this secretion, as in the case of other
glands, a certain amount of watery fluid passes."

The supporters of the filtration theory have however to explain
how it is that a filtrate from the albumen-containing blood-serum
is normally quite free from albumen, or if not quite free contains
it in infinitesimal quantity. According to them the capillary
loops of the glomeruli, with their covering of epithelium, form
but a passive filtering membrane. The loops must consequently
obey the same laws as, and in their action generally must cor-
respond to, other simple animal membranes. Now all other
" transudations " contain albumen ; fresh animal membranes,
also, when employed as filters permit the transudation of
albuminous substances, and this not in small quantities but in
large. Thus Runeberg,^ filtering through a sheep's intestine
blood-serum (from a horse) containing 8*4 per cent, of albumen,
found that at a pressure of 100 ccm. of water, or about 75 mm.
of mercury, the filtrate might contain as much as 80 per cent, of
albumen ; at a pressure of 10 mm. of mercury from 6"54 to 7*8
per cent. And if the thickness of the membrane be a factor of
any importance, the filtration of albumen through the delicate
glomerular wall ought surely to be still more complete.

Yet, as Grainger Stewart has shown that, even with the most
delicate test, namely picric acid — a test that indicates the
presence of albumen in the proportion of 000015 in the 100
parts 2 — when he examined the urine of 505 presumably healthy
individuals he could detect albumen in little over 32*8 per cent,
of the cases. And here the urines tested were forenoon or noon
specimens ; they were passed at the period when physiological .
albuminuria is most prone to become apparent. And of the
32'8 per cent., in 17'8, or more than one-half, albumen could
not be discovered by the addition of cold nitric acid ; in other
words, the amount of albumen present did not exceed 0'003
per cent. Similarly among 525 patients taken at random ^ only

* Runeberg, Arch. d. Beilkunde, vol. xviii. (1877.)

2 Grainger Stewart, loc. cit, p. 10.

' Private, indoor and outdoor hospital, children's hospital, fever, and maternity
patients ; the fever specimens to the number of fifty were tested upon the day
on which it seemed most likely that albumen would be found in each variety of
zymotic disease.

GLOMERULI OF TEE KIDNEY.

247

187 (or 35"6 per cent.) of the urines showed the presence of
albumen, 'and in fifty-seven of these (or 108 per cent.) the
presence was only discernible by adding picric acid. Further,
Grainger Stewart found that even after considerable concentra-
tion albumen is not to be discovered in what he (as I think
rightly) terms normal urine.^ I cite these figures of Grainger
Stewart, instead of those of numerous other observers, in the
first place because his series embraces the largest number
of observations, and in the second because the percentage of
cases in which he discovered the presence of albumin-
uria was not lower but higher than in almost all the previous

series.

This difference between the action of membranes outside the
body, and the result of glomerular activity within it, of
necessity demands explanation. If the glomeruli act by trans-
udation or filtration, the absence of easily recognisable quantities
of albumen in the urine must be accounted for.

By a modification of the " mechanical " theory ^ the absence
of albumen in the normal urine is explicable on the supposition
that the albumen transuded through the glomeruli is actively
re-absorbed by the cells of the tubules ; but, apart from the
fact that the main principles of Liidwig's theory have, one after
the other, been proved insufficient to elucidate the various
phenomena of renal excretion, there is the evidence of Senator *
that the cells of the tubuli, instead of absorbing albumen, are
capable under certain conditions of excreting this substance ;
though, as Senator holds that this excretion is more of the
nature of an exudation, I am not desirous of laying too much
weight upon this point. Nor does the theory of albuminuria
offered by Grainger Stewart appear more satisfactory. He
inclines to the opinion that " the blood-pressure in the capillary
loops, and the walls of these vessels with their epithelial cover-
ing, are so balanced as to permit of the transudation of fluid,
and yet completely to prevent the passage of albumen " ; and
he immediately adds, " at all events we may hold with certainty

■i Grainger Stewart, loc. ci<. p. 19.

^ Ludwig's original theory did not take into account the phenomena of
albuminuria.
8 Senator, loe. cit. p. 57. >

248

ON THE FUNCTIONS OF TEE

that water is mainly eliminated by filtration through these
structures." Apart^from the slight ambiguity in the first of the

8TSLLATE VEINS.

Interlobular vein.

yfi

Interlobular vein. —

Vasa recta. — [

Venous bundles.

Bundles of venules.

Interlobular vein.
Interlobular artery.

Glomerulus.

Interlobular artery.
Interlobular vein.

Arteriae rectse.
Interlobular vein.
Interlobular artery.

Arteries rectse.
Arterial bundles.

Bundles of artciiolcs.

Venous plexus aroundftlie)
"if

apices of the pyramids..
Fig. 1. — Diagram of the blood-vessels in the kidney (after Ludwig).

above sentences, this opinion can scarcely gain acceptance.
There is little doubt that normally a very definite blood-pressure

GLOMERULI OF THE KIDNEY.

249

exists in the glomerular lopps ; the greater part of the arterial
supply of the kidney passes into the interlobular arteries, and
so by the vasa afferentia direct to the glomeruli. A high pres-
sure does not prevent the passage of albumen through simple
animal membranes ; and, on the other hand, with a pressure of
75 mm. of mercury, a pressure far below that which in the dog,
and most probably in man, is accompanied by a total cessation
of urinary excretion, the observations of Runeberg show that
albumen continues to transude in large quantities through
membranes outside the body. At what point then must the
" balance " be supposed to occur ?

Fig. 2.— Malpighian glomerulus, va is the afferent vessel which springs from
the interlohular artery ai, and breaks up to foi-m the glomerulus ; ve is the
efferent vessel which conveys the blood from the glomenaJus.

To declare that a comparison such as this, between dead
membranes and those within the living body, is not just, is to
acknowledge that in the living membrane some other factor
comes into play, that the glomerular walls possess specific pro-
perties, and that the laws of filtration and transudation alone are
insufficient to account for their normal action. This, it seems
to me, is but one step from declaring that the glomerular
epithelium is capable of exercising a selective function. Grainger
Stewart, in acknowledging (p. 68) that altered conditions of the
filtering apparatus may sometimes determine albuminuria, and
that it is conceivable that transudation of albumen might result
from changes either in the vessel-walls or in the epithelium of

250

ON THE FUNCTIONS OF THE

the Malpighian tufts, or both, would appear verj' nearly to
admit this ; for in so doing he presupposes a filtering apparatus
at one time preventing, at another admitting, the passage of
albumen.

Senator^ holds that the fluid passing from the vessels of the
glomeruli must certainly {ohnejedes Bcdenkcn) be considered a
transudation and not a grandular secretion, that these vessels
transude only one portion, but that indeed the greater portion,
of the water of the urine, and that they are exceptional in that
the lateral pressure is in them greater than in any other capil-
lary system in the whole body. This last fact, he claims, is
capable of explaining their action with regard to albumeu : the
greater the filtration pressure the greater is in general the
amount of the filtrate and the less the perceutage of albumen
contained, although the total amount of filtered albumen is, in
equal periods of time, greater with higher pressure than with
lower. Thus, according to Senator, to the great lateral pressure
that exists in the glomerular capillaries is due the copious filtrate
through these organs, and this filtrate contains normally a com-
paratively small amount of albumen, although the total amount
of albumen is larger than would be the case were the pressure
less.

I have already referred to Runeberg's observations. From
these it is deducible that through an animal membrane, at the
medium pressure of 73 mm. of mercury, as much as 95 per
cent, of the albumen in solution may pass (the mother-fluid
containing 84 per cent., the filtrate 80 per cent, of albumen).
At but a tenth of this pressure the percentage still remains very
high. It is unlikely that at the ordinary blood-pressure of
120-150 mm. of mercury there would be any great diminution
in the amount of albumen filtered. But what proportion of
albumen do we find in the urine ?

It is well ascertained that, in the majority of casuS, a test
(picric acid) capable of indicating the presence of 00001 5 per
cent, of albumen in the urine is absolutely without etFect. Or,
in other words, 0*00015 per cent, corresponding to 0"000655 grains
in the ounce of urine, and the amount of urine passed during
the twenty-four hours being roughly 50 ounces, the amount of

1 Senator, loc. cit. p. 57.

GLOMERULI OF THE KIDNEY.

251

albumen secreted during the day, in health, must be below
0"0327 grains. Or, allowing that Grainger Stewart has estimated
the delicacy of the picric acid test as thirty times higher than
it really is, even then the amount of albumen excreted during
the day must be less than 1 grain. The normal blood-serum, ac-
cording to Hammarsten, contains 4'516 parts of serum-albumen.
The presence, therefore, of even as much as a grain of albumen
to the ounce of urine, of 2 instead of less than 0015 per
cent., would, I infer, be still insufficient to harmonise with any
theory of urinary filtration ; and that even if, instead of declar-
ing with Senator that the greater portion of the urinary fluid
passes through the glomeruli, we admit that the greater portion
is excreted through the tubules.

The filtration hypothesis presents us with another very grave
difficulty. The blood-serum contains large amounts of two
proteids : an albumen, serum-albumen, and a globulin, serum-
globulin, or para-globulin, in the proportion roughly of three
parts of albumen to two of globulin. In six separate observa-
tions upon human blood-serum, Hammarsten found that the
percentage of the total albumen present varied from 7*1 to 8'1.
And Salvioli ^ found relatively little change in the proportions of
albumen and globulin when he compared different dogs in various
conditions of hunger, and still less when the blood of one animal
was taken at different periods. No one, in fact, has as yet come
across mammalian blood-serum in which only one of the two
proteids has been present. Both of these transude through
fresh animal membranes, and inasmuch as globulin is the more
diffusible of the two, it would not be unreasonable to suppose
that in cases of albuminuria it should the more readily appear in
the urine. We should at least expect the two proteids always to
be present together, and tliab in what within moderate limits
ought to be a fairly constant proportion. But this is singularly
at variance with what really happens. Although in two cases
Estelle'^ states that he found the relation between the two
l)roteid8 in the urine almost exactly corresponding to the rela-
tion in the blood — a statement doubted by Maguire,^ on the

> Snlvioli, ytrch.f. Amt. u. Plnjsiol. (Pliysiologiciil Section), 1881, p. 269.

'■' Estullo, licvHc viomtcllc Ucn Sciences Med. No. 0, 1880.

^ Maguirc, Lancet, vol. i. 1880, \\\\. 1062 uiul 1100. -

252

ON THE FUNCTIONS OF THE

ground that Estelle did not neutralise the urine before adding
magnesium sulphate — in other cases the same observer found
the albuminous urine to contain albumen only, the globulin
being wholly absent.^ Moreover Maguire ^ has shown that the
proportions vary within enormous limits,' and in four casies, three
of the nature of " cyclic " albuminuria and the fourth puerperal,
he discovered globulin alone to be present, with at most only
the faintest possible trace of serum-albumen, which it was im-
possible to estimate. Variations so wide as these can only be
accommodated to a theory of glomerular filtration on the sup-
position that the relative amounts of the proteids in blood-serum
undergo enormous alterations, that sometimes serum-albumen is
absent, or almost absent, and sometimes globulin, a supposition
which again, I think, no one will be prepared to admit. A more
satisfactory conclusion is that the amount, and the relative pro-
portions, of the proteids in the urine are only to a certain extent
dependent upon the composition of the blood-serum ; and that
one of the functions of the healthy glomeruli is to prevent the
removal of albumen and globulin from the blood when these are

^ Estelle's statement with regard to the urine of one patient (loe. eit, p. 711),
" Ce n'eat tovjoura que dc la matUre A " (serum-albumen), is evidently from the
context a misprint, B (globulin) alone being present. But by ii^'ecting a solution
of serum-albumen into the jugular vein of a guinea-pig, Estelle obtained urine
giving the reaction of albumen alone. And in the case of a young dog, to which
amylio alcohol had been given, ho obtained the following results (globulin being
determined by the addition of magnesium sulphate) : — Blood-serum : albumen
6'2 per cent., globulin 6*4 per cent. ; Urine: albumen 0'84 per cent, globulin
0*8 percent. The percentages of proteids in the blood-serum here given are much
larger than those determined by Salvioli (loc. cit.), and the proportion of globulin
present is placed at a figure much above the normal. It is doubtful whether even
0'08 per cent, of globulin was present in the urine, for, as Ott (Zur quantit.
Bestim, d, Eiweiaskdrp, im Ham, Prager ined. JVochenachr. 1884) has pointed
out, magnesium sulphate brings down a portion of the serum-albumen as well, pro-
vided that 0*5 per cent, of acid phosphates bo present in the solution. Neverthe-
less the above figures, even allowing a largo margin for errors of experiment, show
that there is no immediate relation between the proportions of the proteids in the
blood-serum and urine respectively. * Loc. cit,

• The results may be put roughly thus : —

I. Case of granular kidney — albumen : globulin : : 2'S : 1.

II. Case of granular kidney and mitral stenosis — albumen : globulin : : 4 : 1.

III. Coses of aiitemia and albuminuria with probable fatty degeneration of
kidney. Albuminuria, absent at first with rest, came on upon getting up, and
bore distinct relation to the amount of exercise taken — albumen : globulin
:«1:26.

GLOME' 'LI OF THE KIDNEY.

253

present in normal qua.^.dties, but to excrete either or both of
these, if present in definite excess.

If then we are compelled to abandon the theory that glome-
rular activity is of the nature of simple filtration or transuda-
tion, what are the facts and observations in favour of considering
that the glomeruli possess functions of a selective or secretory
nature, permitting certain substances to pass through their walls
and preventing others ?

In the first place the glomeruli are not solely blood-capillaries.
Each capillary loop is covered by a fine membrane, by a single
layer of epithelium composed of cells which, having large easily-
staining nuclei, must be looked upon as having actively vital
properties. And one vital property, that of contractility, they
have been demonstrated by Hedinger ^ to possess. This epithe-
lium is a visceral extension of that lining Bowman's capsule, and
so is a continuation of the definitely glandular lining of the renal
tubules. In the developmental stage the glomerular epithelium
appears as a layer of cubical units, of a type much more in ac-
cordance with the usually accepted idea of the characteristic
gland cell than in the adult stage, where the cells are so closely
united that it is only with the greatest skill that any divisions
are to be recognised, so much so that many deny that there is
any clear cell-boundary at all. The passage of fluid between
the cells would therefore appear to be guarded against ; and that
this epithelial layer can act as a barrier is demonstrated by the
fact that in argyria, as Riemer ^ has shown, the glomeruli are
found darkly-stained by minute granules of precipitated silver.
These granules lie outside the capillary loops, but between them
and their enclosing epithelial membrane. They must therefore
have been carried with the stream of water through the capillary
walls, and have been stopped in their course by the epithelium.
The specific power of the simplest sheet of epithelium to resist
the passage not only of solids but of fluid is well exemplified by
ail experiment of Leber ^ upon th(^ cornea. He found that the
delicate layer of cells forming Descemet's membrane is the sole
agency whereby the cornea is able to resist a pressure so high as

* IlrcUnper, Dmcrtation, quoted to mo by Proft'ssor Heidonhaiii.
"^ Kleiner, Arch.d. ITnlkiindc vol. xvii. p. 344 (1876).
» Leber, Arch, f, Ophthalml, vol. xix. No. 2, p. 125.

j'UyS:

254

ON THE FUNCTIONS OF THE

that of 200 mm. of mercury. Remove this membrane by pencil-
ling, and the fluid easily invades and swells up the cornea. It is
this membrane alone that in the living eye prevents the imbibi-
tion of the aqueous humour, and the production of a swollen
oedematous condition of the cornea.

Apart however from these general considerations, there are
certain observations which go very far to prove the secretory
functions of the glomeruli. After ligaturing the renal arteries
in the frog, or after cutting off the arterial circulation still more
surely by cauterising and 5 o dividing the (three to five) renal
arteries, the blood-supply of the kidney is of a venous nature,
and is confined to that reaching it from the lower limbs and
coming through the renal portal vein. And although M.
Nussbaum^ has pointed out that there is a possible collateral
arterial circulation, it is difficult to see how this can supply
more than the glomeruli of the lower extremity of the organ.
Nothwithstanding this, by injecting " laky blood " (or de-
fibrinised blood containing haemoglobin in solution), I found it
possible to obtain evidence of the passage of haemoglobin
through the walls of the glomeruli of the kidneys generally
within four hours after the injection, and this in cases where
there had been no demonstrable excretion of urine.* On killing
the animal and placing the kidneys momentarily in boiling
water, the haemoglobin was coagulated, and could be seen as a
brownish, granular, but otherwise homogeneous crescent, in the
" capsule chamber " of many of the Malpighian bodies. In other
words, although the blood-pressure had been very greatly
reduced, and the direct arterial supply to the glomeruli cut off,
the glomerular epithelium allowed the passajje of haemo-
globin even when apparently there was no excretion of water
beyond the minimum amount necessary to keep the haemoglobin
in solution.

Here then it would seem evident that the glomeruli had
excreted haemoglobin under greatly lowered pressure, and with-
out any corresponding watery excretion — a condition only
explicable on the assumption tliat the glomerular epithelium
possesses a definite selective secretory activity, as Heidenhain

* M. Nusabaum, PflUgcr's Archiv vol. xli. (1887).
" Adami, Joiirn. qjf Phyisol, vol. vi. p. 382(1880).

GLOMERULI OF THE KIDNEY.

255

had suggested. These observations were confiiiined by experi-
ments upon the dog. The experiments are to be found fully
described in my paper above referred to (p. 398). Sufl&ce it to
say that the passage through the glomeruli of haemoglobin (to-
gether, probably, with some albumen) could with certainty be
demonstrated in animals, in which by lowering the blood-
pressure below 40 mm. of mercury complete anuria had been
induced, the cessation of the urinary flow being determined
not by the empty state of the bladder, but by means of fine
catheters placed in the ureters and connected with graduated
glass tubes. Here again the appearance of concentrated
haemoglobin outside the glomeruli can only be explained by
the hypothesis that the glomerular walls possess selective
functions.

But further, the same serios of experiments showed in
another way that an amount of hsBmof^lobin could be present in
the urine far beyond that explicable by a theory of filtration. In
opposition to the view first propounded by Ponfick,^ Afanassiew,^
as the result of an elaborate investigation, has shown that not
only a part, but all of the haemoglobin in haemoglobinuria passes
through the glomeruli, and that the brown granular appearance
of the cells of the kibuli contm'ti is due to the presence, not of
haemoglobin, but of the products of degeneration and destruction
of the red corpuscles ; and that when pyrogallic acid, for example,
is injected in quantities not sufficient to produce haemoglobinuria,
while it causes a definite destruction of the corpuscles, the brown
granules are to be observed in the cells of the tubules and again
in the sediment of the urine. Nevertheless rnicrochemical ob-
servation failed to detect haemoglobin in this sediment. These
statements of Afanassiew, so far as they refer to the passage
of unaltered hoemoglobin out of the kidney, have recently been
confirmed by Hunter.^

On examining and comparing the amount of hiemoglobin in
equal quantities of the urine and of blood-serum from dogs in
which haemoglobinuria had been induced, I found that there
could be a very great variation in the relative amount contained,

^ I'onfifik, (luoted by Hoidenhain, loc. cit. p. 351.
" AfiinaHsicw, rircliow'n Arch. vol. xcviii. (1881).
•' Iluutor, Laucct, October 0, 1888.

256

ON THE FUNCTIONS OF THE

a variation dependent in part upon the degree of haemoglobin-
uria, but mainly due to the state of renal activity. Thus
diuretics, such as sodium nitrate, caused a dilution of the
haeraoglobiTv-containing urine, although in a given time the
total amount of haemoglobin excreted was markedly increased.^
This pointed to augmented activity of the glomeruli under the
influence of the diuretic. The relation of the haemoglobin in the
*' laky " blood-serum to that in the urine I found to vary from
I'0 : 0'22 2 to I'0 : 3'45 ^ ; or in other words the urine contai, .ed
in the one instance only about one-fiftji of the haemoglobin in the
serum, in the other it held over three times as much. Variations
so great as this, and the possible presence of so much more haemo-
globin in the urine than in an equal volume of blood-serum, can
be accounted for by none of the theories of filtration at present
put before us,

I am aware that Senator ^ has pointed out what is perhaps an
error in my previous paper. It was there stated that if an
excretion contained more of a given substance per unit-volume
than did the original fluid, then some other laws beyond those
of filtration must necessarily be at work. Now W. Schmidt ^
has found that in the filtration of solutions of gum and salt, and
gum and urea, the filtrate may be richer in sodium chloride to
the extent of from 002 to 0*07 per cent, and in urea from 0*006
to 008 percent. And Runeoerg^ and Loewy, ^ in a series of
observations upon albumen solutions containing salt, found that
the salt in the filtrate might be one-tenth (Runeberg), and one-
half (Loewy), more per unit-volume than in the original fluid.
To all these observations objections may be brought. The
separate results of each of the three appear to vary without
adequate cause. Thus both Runeberg and Loewy found now
more, now less, salt in the filtrate than in the mother-fluid. Nor
again is there any consonance between the amount of excess
found possible by each observer. But even granting that a
filtrate may contain, as these observers contend, some increase
in the relative amount of any one or more constitutents over

1 Loc. cit. p. 415. « Ibid, p. 417. ' Ibid. p. 407.

» Seiifttor, FircJiow's Archiv vol. cxi. p. 228 (1888).

■• W. Sclimidt, Jnnah d. Phynik vol. cxiv. pp. 364- 389 (1861).

" Runeberg, loc. cit. p. 55.

^ AiX. Loewy, Zcitschr.f. phj/siol. Chcmie vol. ix. p. 637 (1885).

GLOMERULI OF THE KIDNEY.

257

' hsemoglobm-
itivity. Thus
lution of the
ven time the
dly increased.^
ruli under the
lOglobin in the
to vary from
rine contai.ed
aoglobin in the
ch. Variations
ih more hsemo-
ood-serum, can
tion at present

t is perhaps an
;ed that if an
unit-volume
J beyond those
7 W. Schmidt ^
m and salt, and
Lum chloride to
irea from 0*006
' in a series of
salt, found that
berg), and one-
i original fluid,
brought. The
vary without
)ewy found now
)ther-fluid. Nor
lount of excess
granting that a
, some increase
astitutents over

» Ibid. p. 407.
861).

1885).

the amount present in the original solution, it is clear that not
even the most favourable of their results can explain the great
increase I have found in the proportion of haemoglobin in the
urine over that iu the blood-serum, an iacrease of nearly 250
per cent, and one most striking to the naked eye.

In his experiments upon the ilberkhende kidney — that is to
• say, on the kidney after extirpation — Immanuel Munk ^ arrived
at similar results with regard to other substances which are
generally considered to be excreted through the glomeruli, using
easily-diffusible salts such as the chloride, phosphate, and sulphate
of sodium, and also sugar. Thus he determined that the secre-
tion was without exception richer in chloride of sodium than
the blood-serum passed through the kidney, to the extent of
from 20 to 67 per cent. ; in the case of sulphate of sodium 45
to 74 per cent., and in the case of sugar 60 to nearly 90 per cent.
The method employed cannot however be considered wholly satis-
factory. An organ removed from the body may in the absence
of central nervous influence be more easily experimented upon ;
but no external warmth, and no artificial circulation commenced
a quarter of an hour or more after removal of the organ from
the abdomen, can ever replace exactly, or even nearly, the bodily
conditions. Nevertheless positive results such as these (coupled
with the fact that Munk was able to obtain under these con-
ditions the synthesis of hippuric acid) cannot be explained
away ; rather it is to be considered that had the organ been in
the body the results would have been still more marked. When,
however, Munk declares that he cannot reconcile his haemcglo-
binuria observations with mine, then I submit the implied
criticism is invalid. Because in his extirpated kidney, with its
greatly-dirainished vitality, he could produce no increase in
the percentage of haemoglobin in what he himself terms the
' artificial ' urine over that in the bloood-serum, he is still far
from proving that under more normal conditions the increase
does not obtain.

There is, then, direct and indirect evidence of the secretory

activity of the glomeruli, evidence which would seem clearly to

indicate that the passage of fluid through these bodies is not a

mere transudation. It will be evident from what has preceded

^ Iininauucl Munk, Virchoiv'a Archiv vol. cvii. p. 307 (1887).

Thii Practitioner.— Vol. xlii. No. 4. t

258

ON THE FUNCTIONS OF THE

tliat I do not claim for the glomerular epithelium auy synthetic
power : I do not say that the cells have the power of forming
from the substances brought to them by the blood any new
substance. Ail that I argue is that they have a selective power,
and to this extent must be looked upon as active and not passive,
as producing a secretion and not a transudation. From many con-
siderations I am led to the opinion that there are two forms of
secretory cells in the organism — the simple or selective secretory
cells (in this category are to be included the glomerular walls, and
most probably the epithelium lining the whole vascular tract), and
the more complex synthetic or metabolic secretory cells, having
still more extensive powers, of which the usually accepted
glandular cells, such as those of the liver and of the tuhuli contorti,
are good examples.

Finally, assuming what I have shown to be most probable,
first, that the secretion of urine depends not so much upon the
blood-pressure as upon the rate of flew of the blood through the
kidney ; and, in the second place, that the glomerular epithelium
has selective secretory powers, let me rapidly indicate the factors
which go to determine the appearance of albuminuria.

That albumen, when it appears in the urine, passes through
the glomeruli, has been demonstrated by so many observers that
there is no need here to state the methods by which this state-
ment can be verified. That some of the albumen may have
its or gin from the cells of the tuhuli uriniferi, Senator's
experiments would seem to prove, and it is not improbable that
in parenchymatous nephritis and in venous engorgement of the
kidney a certain, and it may be a large, portion of the albumen
originates from the atfected cells of the tuhuli.

That normally albumen is present in the urine in infinitesimal
quantities, if indeed it be not wholly absent, can scarce admit of
denial. This absence is to be considered as due to the healthy
state of the cells of the uriniferous tubules, and more especially
to the normal functional activity of the glomerular epithelium.
This epithelium possesses the power of preventing the passage
of albumen and globulin out of the blood-serum in ordinary con-
ditions of the body, provided these are not present in excess ;
and the amount of albumen allowed to pass by the glomerular
epithelium, while in certain cases dependent upon the presence

GLOMERULI OF THE KIDNEY.

259

n auy synthetic
wer of forming
blood any new
selective power,
ind not passive,
rrom many con-
re two forms of
lective secretory
rular walls, and
cular tract), and
ry cells, having
3ually accepted
i tiibuli contorti,

most probable,
much upon the
»od through the
ular epithelium
icate the factors
auria.

passes through
^ observers that
lich this state-
men may have
iferi. Senator's
mprobable that
rgement of the
)f the albumen

of increased quantity, or altered quality, of the albumen in the
blood, is in the main determined by the state of the glomerular
epithelium. This when in a state of lowered vitality permits
the egress of a fluid more of the nature of a transudation : the
less the vitality of the epithelium the more nearly does the
fluid resemble a filtration in its constitution, and as a result of
this loss of selective and controlling power the proteids of the
blood-serum may sink to a percentage much below the normal.
These considerations, while applying to the graver forms of
Bright's disease, are capable of explaining also many cases of tran-
sieiit albuminuria. Temporary determination of blood to the abdo-
minal organs, with slight engorgement and slowed venous outflow ;
pressure upon the kidneys, or obstruction to the renal vessels ;
increased viscosity of the blood and diminished rate of flow ;
imperfect respiration, incomplete oxygenation of the blood, and
the presence of excess of carbonic acid ; imperfect metabolism
of food-stuffs ; direct irritation by some specific substance — these,
singly or in combination, by temporarily lessening the rate of
flow through the glomeruli and thus producing imperfect nutri-
tion of their delicately sensitive walls, or by directly leading to
such imperfect nutrition and lowered vitality, will I think be
found sufficient to explain most if not all the cases of transient
albuminuria, febrile, toxic, puerperal, and functional.

in infinitesimal
scarce admit of
to the healthy
nore especially
lar epithelium,
ig the passage
a ordinary con-
sent in excess ;
the glomerular
n the presence

s 2