348 VETERINARY PHYSIOLOGY 



2. Mode of Absorption of Food. — That absorption is not 

 due merely to a process of ordinary diffusion is clearly 

 indicated by many facts. 



(1) Heidenbain has shown that absorption of water from 

 the intestine takes place much more rapidly than diffusion 

 through a dead membrane. 



(2) The relative rate of absorption of different substances 

 does not follow the laws of diffusion. Griibler's peptone 

 passes more easily through the intestine than the more 

 diffusible glucose, while sodium sulphate, which is more 

 diffusible than glucose, is absorbed much less readily. 

 Again, an animal can absorb its own serum under conditions 

 in which filtration into blood capillaries or lacteals is 

 excluded. 



(3) Absorption is stopped or diminished when the 

 epithelium is removed or injured, or poisoned with fluoride 

 of sodium, in spite of the fact that this must increase the 

 facilities for diffusion. 



(4) During absorption, the oxygen consumption by the 

 wall of the gut is increased. 



3. Channels of Absorption. — There are two channels of 

 absorption from the alimentary canal (see fig. 162, p. 383) — 

 (1) the veins, which run together to form the portal vein of 

 the liver, and (2) the lymphatics, which run in the 

 mesentery and, after passing through some lymph glands, 

 enter the receptaculum chyli in front of the vertebral column. 

 From this, the great lymph vessel, the thoracic duct, leads 

 up to the junction of the subclavian and innominate 

 veins, and pours its contents into the blood stream. The 

 lymph formed in the liver also passes into the thoracic 

 duct. 



(1) Proteins. — (1) During the digestion of proteins the 

 number of leucocytes in the blood is enormously increased, 

 sometimes to more than twice their previous number. This 

 is due to an emigration from the red marrow of bone. The 

 digestion leucocytosis passes off in a few hours, but what 

 becomes of the leucocytes is not known. Possibly they are 



