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A MANUAL OF VETERINARY PHYSIOLOGY 



It is not known to what extent the hydrolytic action is necessary 

 before absorption can occur ; certainly it must be carried as far 

 as proteoses and peptones. If the thoracic duct of a dog be 

 ligatured, and a large protein meal given, it is perfectly absorbed 

 as shown by the increase in urea. Clearly the path of absorp- 

 tion for protein is the bloodvessels, the material passing by the 

 portal vein to the liver. From this it might be supposed that 

 proteose and peptone may readily be found in the general 

 circulation, but as a matter of fact, there is no blood in the body, 

 including that of the portal area, which contains even a trace of 

 peptone or proteose ; in fact, these substances in the circulating 

 blood are poisons, give rise to peptonuria, and are excreted 

 by the kidneys. 



Proteose and peptone in their passage through the epithelial 

 cells of the intestinal wall are resynthetised. How and in what 

 way this is brought about is unknown. We saw that the same 

 thing occurred to the fats before they could pass into the lacteals. 

 Proteins administered by any other channel than the digestive 

 canal are excreted — egg-albumin, for instance, if injected 

 into the blood and got rid of by the kidneys. Foreign proteins 

 are of no use until they have passed through the proper laboratory 

 — viz., the intestinal canal — and that something more than 

 splitting the complex protein molecule occurs is evident from 

 the fact that some rearrangement of the molecule occurs which 

 enables it now to be built into and form part of the protein tissues 

 of the living. body. 



The absorption of protein by animals is an important question 

 in feeding. We saw that, in the matter of fat and carbohydrate, 

 the horse was distinctly inferior to ruminants in capacity for 

 absorbing these substances. In the matter of protein absorp- 

 tion the horse is sometimes superior to the ruminant, and in 

 all cases holds his own, as may be seen from the following table : 



Absorption of Water and Salts. — By means of the bloodvessels 

 water is readily absorbed, though all parts of the digestive tract 

 are not equally active in this respect. There is probably no 



