DIGESTION AND ABSORPTION 185 



may be utilized. It is possible that this polypeptide nucleus 

 may be present in the blood as a result of the tearing down of 

 body protein, and that it may not be necessary for it to have 

 been absorbed from the protein digestion products of the diges- 

 tive tract. If polypeptide material is absorbed for the later 

 synthesis of body protein, it would seem to be probable that 

 the stomach as a digestive organ is of primary importance, 

 and that considerable absorption of digestion products would 

 occur before the food mass was further digested. The evidence 

 has lately gone to show, however, that the digestive function of 

 the stomach is of secondary importance and of almost no es- 

 sential character ; the essential digestion and absorption taking 

 place later after the small intestine is reached. It has been 

 shown, too, that almost immediately, even in the cell wall of 

 the small intestine, resynthesis of protein material takes place. 

 We can only say then that while it may be true that absorption 

 of protein digestion products is all in the form of amino-acids, 

 yet it is not fully established, and polypeptide groups may also 

 be absorbed. 



In the end the digestion products are found immediately 

 after absorption in the intestinal wall, and are thence conducted 

 to the portal vein, where both amino-acids and derived protein 

 groups are present. 



Fats. — The absorption of fats takes place in two forms as 

 has been indicated, viz. as salts (soaps) of the fatty acid formed 

 through the reaction of the bile and intestinal alkalies with the 

 free acid resulting from the fat hydrolysis, and in the form of 

 emulsions produced directly by the bile or by the soaps pre- 

 viously formed. The fat thus absorbed is collected first in the 

 lymphatic circulatory system, and from that reaches the blood. 

 Like the proteins, the fats if absorbed wholly as hydrolyzed 

 products and not as free fat (in emulsion), are immediately in 

 the intestinal wall resynthesized to fat. The question of 

 whether free unchanged fat is directly absorbed is still open, 

 but the experiments with hogs fed with cottonseed oil, in which 

 the lard shows positive proof of the presence of cottonseed oil, 



