same is true to a much less extent with an ordinary filter paper the smooth side
of the filter paper ought always to be placed next the fluid to be filtered]. There
is a similar difference with the gastric and intestinal mucous membrane.

Filtration of the soluble substance may take place from the canal of
the digestive tract when: (1) The intestine contracts and thus exerts
pressure upon its contents. This is possible when the tube is narrowed
at two points, and the musculature between these two points contracts
upon the fluid contents. (2) Filtration, under negative pressure, may be
caused by the villi (Briicke). When the villi contract energetically,
they empty their contents towards the blood- and lymph-vessels. The
lymph-vessels remain empty, as the chyle is prevented from passing
backwards into the origin of the lacteal within the villi, owing to the
presence of numerous valves in the lymphatics. When the villi pass
again into the relaxed condition, they again become filled with the
fluids of the intestinal contents.

192. Absorptive Activity of the WaU of the
Intestine.

The process of digestion produces from the food, partly solutions and
partly finely divided emulsions, whose fine particles are surrounded by
an albuminous envelope, the haptogen membrane [of Ascherson], where-
by these particles become more stable. Unchanged colloid substances
may also be present in the intestinal tract.

I. Absorption of Solutions. True solutions undoubtedly pass by
endosmosis into the blood-vessels and lymphatics of the intestinal walls,,
but numerous facts indicate, that the protoplasm of the cells of the tube
take an active part in the process of absorption. The forces concerned
have not as yet been referred simply to physical and chemical
processes.

(1.) The Inorganic Substances. Water and the soluble salts neces-
sary for nutrition are easily absorbed. When saline solutions pass by
endosmosis into the vessels, water must pass from the intestinal vessels
into the intestine. The amount of water, however, is small, owing to
the small endosmotic equivalent of the salts to be absorbed. More
salts are absorbed from concentrated than from dilute solutions (Funke).



396 ABSORPTION OF SOLUBLE CARBOHYDRATES.

If large quantities of salts, with a high endosmotic equivalent, are intro-
duced into the intestine, e.g., magnesium or sodium sulphate, these salts
retain the water necessary for their solution, and thus diarrhoea is
caused (Poiseuille, Buchheim). Conversely, when these substances are
injected into the blood a large quantity of water passes from the intes-
tine into the blood, so that constipation occurs, owing to dryness of the
intestinal contents (Aubert). [M. Hay concludes from his experi-
ments (p. 320), that salts, when placed in the intestines, do not
abstract water from the blood, or are themselves absorbed, in virtue of
an endosmotic relation being established between the blood and the
saline solution in the intestines. Absorption is probably due to
filtration and diffusion, or processes of imbibition other than en-
dosmosis, as yet little understood. The result obtained by Aubert,
which is not constant, is mostly caused by the great diuresis which
the injected salt excites.]

Numerous inorganic substances, which do not occur in the body, are absorbed by
en dosmosis from the intestine, e.g., dilute sulphuric acid, potassium iodide,
chlorate, and bromide and many other salts.

(2.) The soluble carbohydrates, such as the sugars of which the
chief representative is grape-sugar, with a relatively high endosmotic
equivalent. Cane-sugar is changed by a special ferment into invert
sugar, which is a mixture of grape-sugar and Isevulose (p. 370).
Perhaps a very small proportion of the cellulose is changed into
grape-sugar. The absorption appears to take place somewhat slowly,
as only very small quantities of grape-sugar are found in the chyle-
vessels or the portal vein at any time. According to v. Mering, the
sugar passes from the intestine into the rootlets of the portal vein ;
dextrin also occurs in the portal vein. When the blood of the portal
vein is boiled with dilute sulphuric acid, the amount of sugar is in-
creased (Naunyn). The amount of sugar absorbed depends upon
the concentration of its solution in the intestine; hence, the amount
of sugar in the blood is increased, after a diet containing much
of this substance (C. Schmidt and v. Becker), so that it may appear
in the urine, in which case, the blood must contain at least 0'6 per
cent, of sugar (Lehmann and Uhle). A small amount of cane-sugar
has also been found in the blood (Cl. Bernard, Hoppe-Seyler). The
sugar is used up in the bodily metabolism ; some of it is perhaps
oxidised in the muscles (Zimmer).

(3.) The peptones have a small endosmotic equivalent (Funke), a 2-9
per cent, solution = 7-10. Owing to their great diffusibility, they are
readily absorbed, and they are. the chief representatives of the proteids
which are absorbed. The amount absorbed depends upon the concen-



ABSORPTION OF PEPTONES AND PROTEIDS. 397

tration of their solution in the intestine. They pass into the blood-
vessels (Schmidt-Mill heim). When animals are fed on peptones (with
the necessary fat or sugar), they serve to maintain the body-weight
(Maly, Plosz, and Gyorgyai). Only minute quantities of peptone have
as yet been found in the blood (Drosdorff ) ; hence, it is assumed, either
that they are rapidly converted into true albuminous bodies, or that in
part at least, they undergo further decompositions, with which we are
as yet unacquainted. As, however, they can compensate for the total
metabolism of the proteids within the body, we must assume that they
are converted into proteids.

Schmidt-Miilheim has recently found that, four hours after feeding a pig with
fibrin, a large quantity of crystalline propeptone (p. 331) can be obtained from
the blood. When 5 c.c. of a 20 per cent, solution of peptone in 0'6 per cent.
NaCl solution, for every kilo, of a dog, are injected into the blood, death is pro-
duced owing to paralysis of the blood-vessels (compare 28, II,/). Fano is of
opinion that the red blood-corpuscles take up the peptone, and subject it to further
changes.

(4.) Unchanged true proteids filter with great difficulty, and much
albumin remains upon the filter. On account of their high endosmotic
equivalent they pass with extreme difficulty, and only in traces through
membranes. Nevertheless, it has been conclusively proved that un-
changed proteids can be absorbed (Briicke), e.g., casein, soluble myosin,
alkali-albuminate, albumin mixed with common salt, gelatin (Voit,
Bauer, Eichhorst). They are absorbed even from the large intestine
(Czerny and Latschenberger), although the human large intestine
cannot absorb more than 6 grms. daily. But the amount of unchanged
proteids absorbed is always very much less than the amount of
peptone.

Egg-albumin without common salt, syntonin, serum-albumin, and fibrin are not
absorbed (Eichhorst). Landois observed in the case of a young man who took the
whites of 14-20 eggs along with NaCl, that albumin was given off by the urine for
4-10 hours thereafter. The amount of albumin given off rose until the third day
and ceased on the fifth day. The more albumin that was taken the sooner the
albuminuria appeared and the longer it lasted. The unchanged egg-albumin
reappeared in the urine. If egg-albumin be injected into the blood, part of it
reappears in the urine ( 41, 2) (Stokvis, Lehmann).

(5.) The soluble fat-soaps represent only a fraction of the fats of
the food which are absorbed ; the greater part of the neutral fats being
absorbed in the form of very fine particles as an emulsion. The
absorbed soaps have been found in the chyle, and as the blood of the
portal vein contains more soaps during digestion than during hunger,
it has been assumed that the soaps pass into the intestinal blood-
capillaries. The investigations of Lenz, Bidder, and Schmidt render
it probable that the organism can absorb only a limited amount of fat
within a given period ; the amount perhaps bears a relation to the



398 ABSORPTION OF FATTY PARTICLES.

amount of bile and pancreatic juice. The maximum per 1 kilo, (cat)
was 0'6 grms. of fat per hour.

It appears as if the soaps reunite with glycerine in the parenchyma
of the villi, to form neutral fats, as Perewoznikoff and Will found, after
injecting these two ingredients into the intestinal canal. C. A. Ewald
found that fat was formed when soaps and glycerine were brought into
contact with the fresh intestinal mucous membrane. Perhaps this is
the explanation of the observation of Bruch, who found fatty particles
within the blood-vessels of the villi.

Absorption Of Other Substances. Of soluble substances which are intro-
duced into the intestinal canal, some are absorbed and others are not. The
following are absorbed alcohol, part of which appears in the urine (not in the
expired air), viz. , that part which is not changed into C02 and H2 O, within the
body ; tartaric, citric, mali c, and lactic acids ; glycerine, inulin (Komanos) ; gum
and vegetable mucin, which give rise to the formation of glycogen in the liver.

Amongst colouring matters alizarin (from madder), alkannet, indigo-sulphuric
acid, and its soda salt are absorbed ; hsematin is partly absorbed, while chlorophyll
is not. Metallic salts seem to be kept in solution by proteids, are perhaps
Absorbed along with them, and are partly carried by the blood of the portal vein
to the liver (ferric sulphate has been found in chyle). Numerous poisons are very
rapidly absorbed, e.g., hydrocyanic acid after a few seconds; potassium cyanide
has been found in the chyle.

II. Absorption of the smallest particles. The largest amount of the
fats is absorbed in the form of a milk-like emulsion formed by the
action of the bile and the pancreatic juice, and consisting of excessively
small granules of uniform size (v. Frey). The fats themselves are not
chemically changed, but remain as undecomposed neutral fats. The
particles seem to be surrounded by a delicate albuminous envelope, or
haptogen membrane, partly derived from the pancreatic juice [probably
from its alkali-albuminate]. The villi of the small intestine are the
chief organs concerned in the absorption of the fatty emulsion, but the
epithelium of the stomach and that of the large intestine also take a
part. The fatty granules are recognised in the villi (1) Within the
delicate canals? (p. 387) in the clear band of the epithelium (Kolliker).
[It is highly doubtful if the vertical lines seen in the clear disc of the
epithelium of the intestine are due to pores.] (2) The protoplasm of
the epithelial cells is loaded with fatty granules of various sizes during
the time of absorption, while the nuclei of the cells remain free, although,
from the amount of fat within the cells, it is often difficult to distinguish
them. (3) The granules pass into the spaces of the parenchyma of the
villi; these spaces communicate freely with each other. (4) The
origin of the lacteal in the axis of the villus is found to be filled with
fatty granules.

The amount of fat in the chyle of a dog, after a fatty meal, is 8-10
per cent., while the fat disappears from the blood within thirty hours.



ABSORPTION OF FATTY PARTICLES. 399

With regard to the forces concerned in the absorption of fats,
v. Wistinghausen proved, that when a porous membrane is moistened
with bile, the passage of fatty particles through it is thereby facilitated,
but this fact alone does not explain the copious and rapid absorption
of fats. It appears probable, that the protoplasm of the epithelial cells
is actively concerned in the process, and that it takes the particles into
its interior. Perhaps a fine protoplasmic process is thrown out by
these cells, just as pseudopodia are thrown out and retracted by lower
organisms. It is possible that absorption may take place through the
open mouths of the goblet-cells. The protoplasm of the epithelial cells
is in direct communication with the numerous protoplasmic lymph-cells
within the reticulum of the villi, so that the particles may pass into
these, and from them through the stomata (?) between the endothelial
cells into the central lacteal of the villus. According to this view, the
absorption of fatty particles, and perhaps also the absorption of true
proteids, is due to an active vital process, as indicated by the observa-
tions of Briicke and v. Thanhoffer. This view is supported by the
observation of Griinhagen, that the absorption of fatty particles in the
frog is most active at the temperature at which the motor phenomena
of protoplasm are most lively. That it is due to simple filtration alone
is not a satisfactory explanation, for the amount of fatty particles in the
chyle is independent of the amount of water in it. If absorption was
chiefly due to filtration, we would expect that there would most
probably be a direct relation between the amount of water and the fat
(Ludwig and Zawilsky). [The observations of Watney have led him
to suppose that the fatty particles do not pass through the cell
protoplasm to reach the lacteal, but that they pass through the cement-
substance between the epithelial cells covering a villus. If this view
be correct, the absorbing surface is thereby greatly diminished.]

[Schafer suggests that the leucocytes, which have been observed
between the columnar cells of the villi of the small intestine, are carriers
of at least part of the fat from the lumen of the gut to the lacteal ; they
also, perhaps, alter it for further use in the economy (p. 389)].

The activity of the cells of the intestine with pseudopodial processes may be
studied in the intestinal canal of Distomum hepaticum. Sommer has figured these
pseudopodial processes actively engaged in the absorption of particles from the
intestine.

Spina observed that the intestinal epithelium of the larvse of flies shortened
when they were stimulated with electricity, and absorbed fluid from the intestinal
canal. The cells of the villi of the frog also react to electrical stimulation.

The increase in the size of the cells occurs simultaneously with the contraction
of the intestine. Spina also supports the view that the cells, in virtue of their
activity, possess the property of absorbing fluid from the intestinal contents and
again giving it up. An exchange of fluids in the opposite direction never takes place.

The statements of former observers that particles of charcoal, pigments, and



400 INFLUENCE OP NE&VES ON ABSORPTION.

even mammalian blood-corpuscles (in the frog) were absorbed by the epithelial
cells of the intestine, and passed into the blood, are erroneous. Even for the
absorption of completely fluid substances, endosmosis and filtration seem to be
scarcely sufficient. An active participation of the protoplasm of the cells seems
here also in part at least to be necessary, else it is difficult to explain how very
slight disturbances in the activity of these cells e.g., from intestinal catarrh
cause sudden variations of absorption, and even the passage of fluids into the
intestine.

If absorption was due to diffusion alone, when alcohol is injected into the
intestine, water ought to pass into the intestine, but this does not occur. Brieger
found that the injection of a O'5-l per cent, solution of salts into a ligatured loop
of intestine did not cause water to pass into the intestine; but it appeared when
a 20 per cent, solution was injected.

193. Influence of the Nervous System,

With regard to the influence of the nervous system upon intestinal
absorption we know very little. After extirpation of the semi-lunar
ganglion (Budge), as well as after section of the mesenteric nerves
(Moreau), the intestinal contents become more fluid, and are increased
in amount. This may be partly due to diminished absorption, v.
Thanhoffer states, that he observed the protrusion of threads from the
epithelial cells of the small intestine only after the spinal cord, or the
dorsal nerves, had been divided for some time.

[Matthew Hay injected saline solutions directly into the exposed intestine. He
found that a 20 per cent, solution of sulphate of soda always excites a profuse
secretion, but that a 10 per cent, solution only does so, or rather, that it only
increases in bulk, when injected in sufficient quantity a certain weight of salt
failing to increase the bulk of the fluid secretion when dissolved as a 10 per cent,
solution, but exciting a profuse secretion when forming a 20 per cent, solution. Se-
cretion, he has reason to believe, is active in both perhaps, almost equally active
but absorption is greatly impeded in the'case of the concentrated salt, by its injurious
action on the absorptive mechanism of the mucous membrane. Moreau has recently
maintained that, under such circumstances, there is actually no absorption, but
Hay has disproved this, by observing that strychnia injected into a loop of intestine,
containing the concentrated salt, still causes death, although after an interval three
times longer than when the loop contains a 10 per cent, solution of the salt.

Hay has also observed that the local effect of a ligature applied to the intestine
is to excite secretion from the mucous membrane in its immediate vicinity, and
therefore add to the bulk of the saline solution ; whereas the reflex effect of a
ligature, as exercised through the nervous system, is to diminish the quantity of
the secreted fluid in a remote portion of the intestine, probably by stimulating and
accelerating absorption. Division of the vagi does not affect the nature or the
quantity of the secretion].

194. Feeding with "Nutrient Enemata."

In cases where food cannot be taken by the mouth e.g., in stricture of the
tesophagus, continued vomiting, &c., food is given per rectum (Celsus, 3-5 A.D.).
As the digestive activity of the large intestine is very slight, fluid food ought to
be given in a condition ready to be absorbed, and this is best done by introducing



LACTEALS AND LYMPHATICS, /^, 401

it into the rectum through a tube with a funnel attached, and allowing the food
to pass in slowly by its own weight. The patient must endeavour to retain the
enema as long as possible. When the fluid is slowly and gradually introduced, it
may pass above the ileo-csecal valve.

Solutions of grape-sugar, and perhaps a small amount of soap solution, are
useful; and amongst nitrogenous substances the commercial flesh, bread, or milk
peptones of Sanders-Ezn, Adanikiewicz, in Germany, and Darby's fluid meat in
this country, are to be recommended. The amount of peptone required is I'll
grms. per kilo, of body- weight (Catillon); less useful are butter-milk, egg-albumin
with common salt. Leube uses a mixture of 150 grms. flesh, with 50 grms.
pancreas and 100 grms. water, which he injects into the rectum where the proteids
are peptonised and absorbed. The method of nutrient enemata only permits
imperfect nutrition, and at most only of the proteids necessary for maintaining
the metabolism of the body is absorbed (v. Voit, Bauer).



195, Chyle-Vessels and Lymphatics.

Within the tissues of the body, and even in those tissues which do
not contain blood-vessels e.g., the cornea, or in those which contain
few blood-vessels, there exists a system of vessels or channels which
contain the juices of the tissues, and within these vessels the fluid
always moves in a centripetal direction. These canals arise within
the tissues in a variety of ways, and unite in their course to form
delicate and afterwards thicker tubes, which ultimately terminate in
two large trunks which open at the junction of the jugular and sub-
clavian veins ; that on the left side is the thoracic duct, and that on
the right, the right lymphatic trunk.

Lymphatics. With regard to the lymph and its movements in
different organs, it is to be noticed that this occurs in different ways
in different places. (1) In many tissues, the lymphatics represent the
nutrient channels, by which the fluid which transudes through the
neighbouring vessels is distributed, as in the cornea and in many
connective tissues. (2) In many tissues, as in glands e.g., the sali-
vary glands (Gianuzzi) and the testis, the lymph-spaces are the first
reservoirs for fluid, from which the cells during the act of secretion
derive the fluid necessary for that process. (3) The lymphatics have
the general function of collecting the fluid which saturates the tissues,
and carrying it back again to the blood. The capillary blood-system
may be regarded as an irrigation system, which supplies the tissues with
nutrient fluids, while the lymphatic system may be regarded as a
drainage apparatus, which conducts away the fluids that have trans-
uded through the capillary walls. Some of the decomposition pro-
ducts of the tissues, proofs of their retrogressive metabolism, become
mixed with the lymph-stream, so that the lymphatics are at the same
time absorbing vessels. Substances introduced into the parenchyma of
the tissues in other ways, e.g., by subcutaneous injection, are partly

26



402 ORIGIN OF THE LYMPHATICS.

absorbed by the lymphatics. A study of these conditions shows, that
the lymphatic system represents an appendix to the Uood-vascular
system, and further, that there can be no lymph system when the
blood-stream is completely arrested; it acts only as a part of the
whole, and with the whole.

Lacteals. When we speak of the lymphatics proper as against
the chyle-vessels or lacteals, we do so from anatomical reasons, because
the important and considerable lymphatic channels coming from the
whole of the intestinal tract are, in a certain sense, a fairly independent
province of the lymphatic vascular area, and are endowed with a
high absorptive activity, which, from ancient times, has attracted the
notice of observers. The contents of the chyle-vessels or lacteals are
mixed with a large amount of fatty granules, giving the chyle a white
colour, which distinguishes them at once from the clear watery con-
tents of the true lymphatics. From a physiological point of view,
however, the lacteals must be classified with the lymphatics, for, as
regards their structure and function, they are true lymphatics, and
their contents consist of true lymph mixed with a large amount of
absorbed substances, chiefly fatty granules. [The contents of the
lacteals are white only during digestion, at other times they are clear
like lymph].

196. Origin of the Lymphatics.

The mode of origin of the lymphatics varies within the different
tissues. The following modes are known :

1. Origin in Spaces. Within the connective-tissues (connective-tissue proper,
bone), are numerous stellate, irregular, or branched, spaces which communicate with
each other by numerous tubular processes (Fig. 157, s) ; in these communicating
spaces lie the cellular elements of these tissues. These spaces, however, are not
completely filled by the cells, but an interval exists between the body of the cell
and the wall of the space, which is greater or less according to the condition of
movement of the protoplasmic cell. These spaces are the so-called "juice-canals "
or "saftcanalchen," and they represent the origin of the lymphatic vessels (v.
Recklinghausen). As they communicate with neighbouring spaces, the movement
of the lymph is provided for. The cells which lie in the spaces, and which were
formerly but erroneously regarded by Virchow as the origins of the lymphatics,
exhibit amoeboid movements. Some of these cells remain permanently, each in its
own space, within which, however, it may change its form these are the so-called
" fixed " connective-tissue corpuscles, and bone-corpuscles while others merely
wander or pass into these spaces, and are called " wandering cells," or "leucocytes;"
but the latter are merely lymph-corpuscles, or colourless blood-corpuscles which
have passed out of the blood-vessels into the origin of the lymphatics. These cells
exhibit amosboid movements. These spaces communicate with the small tubular
lymphatics the so-called lymph-capillaries (L). The spaces lie close together
where they pass into a lymph- capillary (a). The lymph-capillary, which is
usually of greater diameter than the blood capillary, generally lies in the middle



ORIGIN OF THE LYMPHATICS.



403




Fig. 157.

Origin of lymphatics From the central tendon of the diaphragm of a rabbit
(semi-diagrammatic) ; s, the juice-canals, communicating at x with the
lymphatics; a, origin of the lymphatics by the confluence of several juice-
canals. The tissue has been stained with nitrate of silver.