. / BSORPTION OF C \1 RBOH ) DR. 1 TES AND PROTEIDS. 433 
re are thus two channels of absorption Leading to the systemic 
blood Btream. One by the capillaries of the villus, passing through tin' 
liver; the other by the lacteals, vid the abdominal lymphatics, to the 
thoracic duct leading directly to the subclavian vein. 
vrption of water. — It has been shown by Heidenhain 1 that by 
far the greater share of the water absorbed from the small intestine 
is taken up by the capillaries of the villus and not by the lacteals. 
When large quantities of dilute saline solution (0:3 per cent.) are injected 
into the small intestine, the rate of lymph flow in the thoracic duct 
is not markedly increased, unless so much salt solution is injected at one 
time that the" intestine becomes forcibly distended. Zawilsky 2 also 
found that even during active fat absorption there was no meat increase 
in the amount of lymph flowing from the thoracic duct; the lymph 
became charged with an exceedingly fine emulsion of fat, but was not 
largely increased in quantity. 
"The considerable absorption of water which commences in the lower 
end of the ileum, and goes on throughout the entire length of the large 
intestine, causing the thin chyme of the upper part of the small intestine 
to become semi-solid, and finally to assume the consistency of the faeces, 
is also carried out by the agency of capillary blood vessels, so that 
practically all the water absorbed from the intestine is taken up by the 
blood stream. The blood is not diluted to a corresponding extent in the 
process: in fact, even with the absorption of an excessive amount of 
water, as in Heidenhain's experiments above quoted, the composition of 
the blood is little altered. The absorbed water in such a case of 
excessive absorption passes at first into the lymph which bathes the 
tissues, to be afterwards brought out and gradually eliminated by the 
kidneys as the excess in the blood diminishes. 
Absorption of soluble constituents. 3 — All those substances which leave 
the epithelial cell in solution, are also carried away from the lymph 
spaces of the villus by the capillaries. 4 This has been shown chiefly by 
observations made during active absorption of these several constituents, 
on the rate of flow in the thoracic duct, the constitution of the lymph so 
flowing, and the effects of ligature of the duct or diversion of the stream 
to the'exterior. Direct analyses of the blood of the portal vein, as com- 
pared with the systemic blood, do not yield trustworthy results ; partly 
because of the difficulty of making very exact determinations in such a 
complex fluid as blood serum ; still more because of the very small change 
in composition which is sufficient to account for the carriage of a great 
weight of absorbed substance, by reason of the copious flow which takes 
place through the capillaries, esx>ecially when active digestion is in 
progress. 
If a cannula be inserted into the upper end of the thoracic duct, and 
the rate of flow of the lymph stream measured, as well as the amount of 
proteid contained therein, neither of these is found materially to alter, 
whether the animal (dog) be fasting, or active proteid digestion be going 
1 Arch. f. d. ges. Physiol., Bonn, 1888. Supp. Heft, Bd. xliii. S. 53; 1894, Bd. lvi. 
S. 579. 
2 Arb. a. d. physiol. Anst. zu Leipzig, 1876, Bd. xi. S. 161. 
3 For the Absorption of fats and fatty acids, see p. 443. 
4 It is often stated that all the dissolved intestinal contents are so absorbed, but if, as 
is probable, fats are absorbed in soluble form, such a statement is obviously incorrect. Only 
those constituents which remain soluble, after the action of the absorbiug cells, pass into 
the capillaries. 
VOL. I. 28 
