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FILTRATION.



283



On the other hand, the older experiments of Schmidt ^ with gum
and albumin gave quite opposite results ; thus (p. 364 of 1861 paper) —

Allmmm through Ox Pericardium.



Concentration of Original
Solution per Cent.


Pressure.


Per Cent. Albumin in Filtrate.

Per Cent. Albumin in Original

Solution.


1-6


i 220 mm.
[ 120 mm.


•7037
•6638


3-5


{ 220 mm.
[ 120 mm.


•7050
■7742



And the experiments of Gottwalt^ and v. Eegeczy ^ are in agreement
with those of Schmidt.

According to Lowy/ who filtered serum and egg albumin solutions
through pig's bladder at constant pressure, rise of temperature affects
the quantity of the organic solids filtering more than the inorganic, and
such slight temperature changes as from 37°'5 to 41°^5 C. have a distinct
effect.

It is therefore evident that our knowledge of the phenomena of filtra-
tion through animal membranes is at present very restricted, and it is
of course impossible to directly apply the results of the above observers
to filtrations in the living body. No experiments, perhaps, have more
clearly pointed out the difference between a dead and living filter than
those of Tigerstedt and Santesson ^ with the frog's lung. A fresh frog's
lung, filled with •G per cent, sodic chloride solution, will stand a pressure
of some 13 or 14 mm. of mercury without filtering for many hours ;
heating in water at 54° C, or treatment with weak acetic acid, frog's bile,
weak sodic hydrate, or distilled water, at once, however (presumably by
killing the cells), allows filtration. Leber,^ moreover, showed that the
fresh cornea, provided the epithelium of. the membrane of Descemet is
intact, will stand a pressure of 200 mm. of mercury, but at once
allows filtration to occur when the epithelium is removed, the tissue
of the cornea itself allowing fluid to pass.

It must be confessed that experiments on living membranes (and
these alone) can give any information of real value ; and, furthermore, it
must be remembered that filtrations in the body are, as a rule, accom-
panied by osmotic phenomena, since filtration must nearly always occur
from one solution into another, and not into air, as in most experiments.

In concluding this article, a word must be said with regard to the
theory that in some cases the cells of a part take some active part in
moving solutions across membranes. So little is known of cell mechanics,
that if such a process does take place we have certainly no conception
of its modus operandi, and it is at least probable that a process con-
sidered to-day as a " vital action " may in the future become capable
of a simpler explanation. Certainly, if the same solution is placed on



^ Loc. cit. - Loc. cit. ^ Loc. cit. •* Loc. cit.

« Arch./. OpUh., Leipzig, 1873, Bd. xix. Abth. 2, S. 125.



^ Loc. cit.



2 84 DIFFUSION, OSMOSIS, AND FIITRATION.

either side of a living membrane, and a current is found to pass from
one side to the other, when the possibilities of filtration and electro-
osmose are excluded, we have no physical explanation. Thus Heiden-
hain ^ has demonstrated that serum is absorbed by the intestine. The
pressure in the gut in relation to that in the capillaries, it is true, was
not measured, and the serum was not the animal's own serum, yet these
objections are not of great force, especially the former, since an excess
of pressure in the intestine would probably cause collapse of the capil-
laries or venules.^ It is absurd to maintain that the motion of the
blood in the capillaries asjDirates the serum through the epithelium,
because the rate of the blood stream is too slow to have any appreciable
effect in this direction, and weak salt solution is moved across exsected
and still living gut with equality of pressure on the two sides and no
stream.^

This class of absorption experiment appears to be the only one in
which it is justifiable to speak of " vital action," for differences in the
ratios of " diffusion " of two substances into serum outside the body,
and in the cavities thereof, are, "per se, no proof of such action, since, as
has been already indicated, the physical permeability of membranes
differs much to one and the same substance ; and again, the fact that a
drug affects the rate of absorption of a substance, after exclusion of the
action of that drug (if any) on the circulation, is as well (and as little)
explained by stating that the permeability of the membrane is altered
by its combination with the drug, as by stating that the activity of the
cells is affected.

In spite of the magnificent labours of Dutrochet, G-raham, Pfeffer,
van 't Hoff, and Arrhenius, the enigma of the physical chemistry of
protoplasm in many cases still puts a limit to the physiologist's concep-
tion of the mode of motion of fluids through the membranes and cells
of the body.

1 Arch./, cl. r/es. Physiol., Bonn, 1894, Bd. Ivi. S. 579.

2 The author has repeated Heidenhain's expetiment, using the animal's own serum, and
measuring the pressure in the gut, and in a mesenteric vein throughout. Active absorption
occurs, of the water, of the oi'ganic, and of the inorganic solids of the serum, when the
pressure in the gut is far below that in a mesenteric vein, and when all the lacteals leaving
the loop have been ligatured.

3geid, Brit. Med. Journ., London, May 28, 1892.



THE PRODUCTION AND ABSORPTION OF LYMPH.

By Ernest PI. Staeling.

Contents. — The Production of LymjDli, p. 285 — The Physical Forces concerned in
the Movement of Lymph, p. 299 — The Absorption of Lymph from tlie Con-
nective Tissues, p. 302 — On the Functions of tlie Lymph in the Nutrition of
the Tissues, p. 310.

The Production of Lymph.

The spleen is the only part of the body where the blood comes in actual
contact with the living cells of the tissue. In all other parts of the
body the blood flows in capillaries with definite walls consisting of a
single layer of cells, and is thus separated from the tissue elements by
these walls and by a varying thickness of tissue. All the interstices of
the tissues are filled with a fluid, lymph,^ which thus acts as an inter-
mediary between blood and tissues. The tissue spaces, which are filled
with lymph, are always found in association with connective tissue.
They have an incomplete lining of endothelial cells, and are connected
with definite channels, lymphatics, by which any excess of fluid in the
part is drained off. The lymphatics all run towards the chest, where
those from the lower limbs as well as from the viscera join to form
a large vessel, the receptaculum chyli, which is continued into the
chest as the thoracic duct. This runs on the left side of the oeso-
phagus, to open into the large veins at the junction of the left internal
jugular with the subclavian vein. A small vessel on the right side
drains the lymph from the right upper extremity and side of the
chest.

Lymph may be collected for examination by placing a cannula in
one of the main lymphatics of a limb, and inducing a flow by move-
ments of kneading and massage, from the lymphatic duct of the neck, or
from the thoracic duct. Since, moreover, the serous cavities of the pleura,
peritoneum, pericardium, and tunica vaginalis are in free communication
with the lymphatic system, any fluid which is normally found in them
may be looked upon as lymph. The various analyses of lymph that
have been made, show that its composition may vary considerably
according to' the locality from which it is derived and the circumstances
under which it is obtained. Certain general characteristics are, how-
ever, common to all specimens of lymph. It is always slightly alkahne,
and clots spontaneously at a variable time after it has left the vessels,

^ Adler and Meltzer {Journ. Expcr. Mod., Baltimore, 1896, vol. i. No. 3) draAv a sharp
distinction between the interstitial fluid of the tissue spaces, and the lymph obtained from
the lymphatics which drain these spaces.



2 86 PROD UCTION AND ABSORPTION OF L YMPH.

forming a colourless clot of fibrin. It contains from 2 to 8 parts
per 100 of soKds, of which about 1 per cent, consists of inorganic
salts, while the rest is made up chiefly of proteids. The proteids are
similar to those of the blood plasma; and it seems that the process of
clotting is identical in the two fluids. The salts vary very little in
different samples of lymph, and are generally described as being present
in exactly the same proportions as in the blood plasma from which the
analysed specimen of lymph was derived. Hamburger has recently
called attention to the existence of minute differences of composition in
the salts of the two fluids, and this difference may be credibly ascribed
to chemical changes effected in the lymph by the tissues over which it
has flowed. All specimens of lymph contain leucocytes, chiefly of the
small uninuclear variety ; these are found in greater numbers after the
lymph has passed through a lymphatic gland. Further information re-
garding the composition of lymph will be found in the article on lymph
and serous exudations (p. 181).

The similarity in composition between liquor sanguinis and lymph
suggests that the latter may be regarded as part of the plasma which
exudes through the capillary wall, bathes all the tissue elements, and is
collected by the lymphatics into the thoracic duct to be returned again
to the blood.

Forces involved in Ijonph production. — Older theories. — As to
the forces involved in its production and the use of this fluid in the
functions of the body, the most various views have been held. Asellius,^
who discovered the lacteals in 1622, thought that these ducts
carried the foodstuffs from the intestines to the liver to be there
elaborated into blood. In order to explain the filling of the lacteals
from the intestines, Asellius invoked the aid of the complicated
mechanism which had already been imagined by Avicenna to account
for the filling of the mesenteric veins. He explained the passage of
chyle to the liver as due partly to the intestinal movements and partly
to the suction-action of the blood vessels and of the liver itself. The
chief factor however was, according to him, the suction-action exerted
by the open months of the lacteals themselves, and he compares the
latter to leeches, which suck blood from any surface to which they are
applied. This theory was overthrown by Pecquet ^ by the discovery of
the connection of the lacteals with the thoracic duct and through this
with the venous system. The general lymphatics w^ere discovered
by Ptudbeck^ and Bartholin^ almost simultaneously. In these authors
we meet with the first conception of lymph apart from absorbed
foodstuff's ; moreover, Bartholin, assuming that this lymph is formed
from the blood, discusses the possible ways by which the fluid could
get from blood vessels to lymphatics. He thinks it possible that
there may be a direct communication between lymphatics and blood
vessels, but is more inclined to the view that the communication is
indirect by means of the parenchyma of the organs. Failing to remark
what Budbeck had already noticed, namely, that the lymph had a salt
taste, and like blood clotted spontaneously, he describes the lymph as
pure water, and imagines that from the blood vessels there is a

^ " De lactiljus sive lacteis vcuis," Basel, 1628.

- " Expeiinicnta nova anatoniica," Paris, 1654.

^ "Nova exercitatio aiiatomica, etc." 1653.

•* " Vasa lymphatica nuper in animantibus inventa," Hafnise, 1653.



THEOR Y OF LUD WIG. 287

transudation of water carrying solids in solution, the solids being taken
up by the tissues, and the pure water which is left over returned by
the lymphatics to the blood. We get here the first conception of the
irrigation theory of tissue nutrition which has played so great a part in
the speculations of later physiologists.

With Hunter 1 and Monro ^ we find a return to the older theory, that
lymph was produced by a process of suction. This indefinite conception,
however, allowed a considerable degree of individual licence as to the
details of the process, and important authors, such as Hunter and
Mascagni,^ recognised the possibility of a simple transudation or filtra-
tion through the blood-vessel walls. This latter view, however, did not
meet with general recognition, physiologists preferring to believe
in the existence of the exhalant arteries which no one had yet seen
or was ever going to see. Thus we find Bichat * definitely asserting
the existence of " vasa exhalantia." Speaking of connective tissues, he
writes : " Chaque cellule du tissue cellulaire est un reservoir inter-
mediare aux exhalants, qui s'y terminent, et aux absorbants qui en
naissent." The absorption through the supposed open mouths of the
lymphatic and lacteal vessels was attributed by most authorities of this
time to capillary attraction, while the onward flow of the fluid in the
lymphatics could, according to Cruickshank, only be explained as due
to the vital activity of Hving cells or tissues. Haller describes the
movement of the chyle from the intestines in exactly the same manner.
Particularly ingenious is Hewson's ^ explanation of the absorption and
movement of chyle in the lacteals. He shows that during life the blood
vessels of the villi and in the papilke of the skin and mucous mem-
brane, by their turgescence, keep the orifices of the lacteals or the similar
openings of the lymphatics patent, so that these are now capable of
attracting like capillary tubes made of hard substances. The further
movement of the chyle and lymph he ascribes to the peristaltic con-
traction of muscular fibres in the walls of the lacteals or lymphatics.

Views very similar to these were held by some of the most dis-
tinguished of subsequent physiologists, such as Prochaska, Fohmann,
Burdach and Henle. In opposition to this mechanical theory of lymph
formation, Johannes Mliller,^ having regard to the apparent power of
choice possessed by the lacteals, some substances being absorbed while
others were left, was inclined to ascribe at any rate the act of absorption
to the vital activities of the living cells of the body.

On the discovery of endosmosis by Dutrochet,'^ many physiologists
believed that at last the riddle of absorption and secretion of lymph was
solved, and from this time onwards we find an invocation, generally
more or less vague, of osmotic action to explain the phenomena of
absorption and secretion.

Theory of Ludwig. — The beginning of the new era in the history
of the physiology of lymph formation is marked by the important
paper of Ludwig and Noll.^ In consequence of experiments on

1 Works, edited by Palmer, London, 1835, vol. iv. p. 299.

- " De venis lymphaticis valviilosis, " 1757.

^ " Vasorum lymphaticorum corporis humaiii historia et iconographia," 1787.

^ "Anatomic gi^m^rale," 1812.

s " A Description of the Lymphatic System, etc.," Collected Works,- Syd. Soc, 1846.

^ "Elements of Physiology," Baly's trans., 1838, vol. i. p. 248.

'' Previous article, p. 273. See also " Cyclopaedia of Anat. and Phys.," art. " Eudosmose."

8 Ztschr.f. rat. Med., 1850, Bd. ix. S. 52.



288 PROD UCTION AND ABSORPTION OF L YMPH.

blood pressure, carried out by the aid of the mercurial manometer of
Ludwig, these authors concluded that the chief factor in the forma-
tion of lymph was the pressure of the blood in the capillaries, and
that in fact the lymph was essentially only the fluid part of blood
which had filtered through the vessel wall into the surrounding
tissues. On arriving in the tissues, this lymph or blood filtrate was
still under a certain pressure, derived from the blood pressure, and
it was this pressure which occasioned the movement of the lymph
into and along the lymphatics. Ludwig concluded that the flow and
composition of the lymph must be explained not only by filtration
of the fluid parts of the blood, but also by processes of osmosis taldng
place between the tissue juices and the blood. He summarises his theory
in the following words : — "The blood which is contained in the vessels must
always tend to equalise its pressure and its chemical constitution with
those of the extra vascular fluids, which are only separated from it by the
porous blood-vessel walls. If, for example, the quantity of blood in the
vessels has increased, the mean blood pressure is also increased, and at
once a portion of the blood is driven out into the tissues by a mere
process of filtration. The same result is brought about when the con-
stitution of the blood is altered by the absorption of food or by increased
excretion by the kidneys, blood, or skin, or when the composition of the
tissue fluids is altered in consequence of increased metaboHc changes
taking place in the tissues. In the latter case, the changes brought
about in the lymph are effected by processes of diffusion." Since it is a
condition of the maintenance of hfe that these chemical changes in the
tissues should go on, and that the waste products should be continually
excreted by the kidneys, lungs, and skin, there must be at the same
time constant changes in the amount and composition of the lymph
produced.^

The testing of this, the mechanical theory of lymph formation and
the lineal descendant of the theory propounded two hundred years
previously by Bartholin, has been the object of all subsequent investiga-
tions dealing with this question. Although we cannot claim to have
arrived at a final decision on the matter, I shall endeavour to show in
the following pages that the two processes — filtration and diffusion —
described by Ludwig, will probably account for the lymph flow and
composition in all the cases which have been sufficiently investigated.

It was shown many years ago by Magendie and others, that chemical
differences between blood and lymph provoked a transference of the
substance that was in excess from one side of the vessel wall to the
other. Thus, if colourmg matters, salts, or sugar be injected into the
blood, they are very shortly afterwards found in the lymph in various
parts of the body. If, on the other hand, these substances be injected
into the tissue spaces or into the pleural or peritoneal cavities, their
existence can very soon be detected in the l3lood, whence they make
their way into the urine. Other instances of the extreme rapidity with
which osmotic interchanges take place Ijetweeh the blood and lymph
will be mentioned later on in dealing with the action of lymphagogues.
Since these interchanges take place after the introduction of abnormal
as well as normal substances into the body, we must assume the general
applicability of the results, and look upon processes of diffusion or
osmosis as one of the factors in regulating the composition of the lymph.
1 "Lehrbuch der Physiologic," 1861, AuB. 2, Bd. ii. S. 562.



THE OR Y OF HEIDENHAIN. 289

Not so successful were Ludwig's attempts to demonstrate a direct
relationship between blood pressure and lymph formation. According
to Ludwig's hypothesis, the amount of lymph produced in any given
part must be proportionate to the difference between the pressure in
the capillaries and the pressure in the extra vascular spaces. In most of
Ludwig's earlier experiments on the subject this condition was found to
hold good. On leading defibrinated blood through a limb, the lymph
production in the limb was found proportional to the pressure at which
the blood was led through it. In the testis Tomsa^ showed that ligature
of the pampiniform plexus caused a large increase in the lymph from
this organ. Paschutin ^ and Emminghaus '^ found that, in the arm and
leg, extensive ligature of the veins led to an increased lymph production.
In all these cases, therefore, an augmented How of lymph was obtained
by raising the capillary pressure of the part. On the other hand, the
two last-named observers were unable to prove any constant alteration
of lymph production incident on vasomotor changes. Thus, in one
experiment, Paschutin divided the brachial plexus of a dog and then
stimulated the cut spinal cord, so that there was constriction of all the
arteries of the body with the exception of those of the fore-limb under
observation. Even this rise of pressure had no effect on the lymph flow
from the fore-limb. A little later, Eogowicz,^ working in Heidenhain's
laboratory, repeated Emminghaus' experiments on the hind-limb with
slight alterations, and found almost invariably a slight increase in the
lymph after section of the sciatic nerve or in consequence of active vaso-
dilatation. He proved, moreover, that the vaso-dilatation of the tongue
produced by excitation of the lingual nerve was followed by an increased
lymph production in the tongue, which might at times amount to an
actual unilateral oedema of this organ.

Theory of Heidenhain, — In dealing with the laws affecting
lymph production, we are hampered by the fact that, from the limbs
of an animal at rest, there is, under normal conditions, no lymph flow
at all, so that, when we wish to study the effects of our various
procedures on the lymph production in the limb, we have artificially
to bring about a lymph flow by kneading and massaging the limb.
This fact introduces at once an arbitrary element into the observa-
tion, and Heidenhain suggested, therefore, that the best mode of
investigating the truth of the filtration hypothesis would be to
experiment on the lymph flow from the thoracic duct. This physio-
logist carried out a long research on the various conditions under
which the lymph flow from the thoracic duct might be increased
or diminished,^ and came to the conclusion that the results of his
experiments were irreconcilable with the filtration doctrine, and that we
must assume that the cells forming the walls of the capillaries take an
active part in lymph formation, i.e. that lymph must be looked upon as
a secretion rather than as a transudation. A very similar conclusion had
been previously arrived at by Tigerstedt,*' mainly on theoretical grounds.

Heidenhain's arguments may be shortly summarised as follows : —

1. Obstruction of the thoracic aorta causes a general fall of arterial

1 Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1862, Bd. xlvi. S. 185.

^ Arh. a. d. physiol. Anst. zu Leipzig, 1873. ^ Ihid.^ 1873.

^Arch.f. d. ges. Physiol., Bonn, 1885, Bd. xxxvi. S. 252.

^ Ibid., 1891, Bd. xlix. S. 209.

^ Mitth. a. d. physiol. Inst, zit Stockholm, 1886.

VOL, I. — 19



290 PROD UCTION AND A B SORPTION OF L YMPH.

blood pressure IdbIow the obstruction. In spite of this fact, the lymph
flow from the thoracic duct may in some cases be unaltered and even
slightly increased.

2. Obstruction of the inferior vena cava above the diaphragm causes
a general fall of blood pressure, and the intestines become apparently
anaemic. The lymph flow from the thoracic duct is largely increased, and
the lymph undergoes chemical changes, becoming more concentrated
than it was before the obstruction. This lymph, according to Heiden-
hain, comes from the intestines, whereas, on obstruction of the portal
vein, these organs yield an increased flow of a lymph which is less
concentrated than normal and contains red blood corpuscles.

3. Heidenhain describes two classes of bodies, which on injection
into the circulation increase the lymph flow from the thoracic duct.

The first class comprises bodies such as commercial peptone, watery
extract of dried leeches or of crayfish. These increase the lymph and
make it more concentrated. They usually cause a lowering of arterial
blood pressure, although by careful injection this may be avoided.

The second class includes crystalloids such as sodium chloride, sugar,
etc. Injection of concentrated solutions of these bodies into the circula-
tion evokes an increased flow of lymph which is less concentrated than
before. Some time after the injection, it is found that the lymph
contains a greater percentage amount of injected substance than does
the blood plasma. There may be a slight rise in the arterial pressure,
but this rise is in no way proportionate to the augmentation in the
lymph flow.

Since, therefore, the lymph flow may be increased without any
corresponding elevation in the blood pressure, and smce the amount of
injected substance in the lymph may rise above that in the blood plasma,
Heidenhain concludes that the processes of filtration and diffusion are
incapable of accounting for the changes observed in the amount and
composition of the lymph ; although he does not deny that, under certain
pathological conditions, such as heart disease and cirrhosis of the liver,



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 40 of 147)