1 84 ORGANIC AGPaCULTURAL CHEMISTRY 



the liver in the form of the three common monosaccharoses, 

 though mostly in that of glucose. It is claimed by some au- 

 thorities that absorption of carbohydrates does take place in 

 the stomach, but if so it is probably only in a limited amount 

 or under special conditions. When such absorption does occur, 

 the products reach the portal vein as just described. 



Proteins. — While some absorption of protein digestion 

 products may occur in the stomach, yet with these food ma- 

 terials, as with carbohydrates, the chief absorption of the 

 products takes place in the small intestine and is completed 

 in the upper part of the large intestine. More than 90 per 

 cent of the digested protein is, however, absorbed before the 

 food mass reaches the large intestine. 



We have shown that the final products of protein digestion 

 are amino-acids, and that the hydrolysis of proteins yielding 

 these products takes place in the small intestine due to the 

 combined action of the pancreatic enzyme trypsin and the 

 intestinal enzyme erepsin. While gastric digestion in the 

 stomach begins with original proteins and ends almost wholly 

 with derived proteins; peptones, and proteoses, the tr3^tic 

 digestion beginning at the same point, i.e. with original pro- 

 tein, carries the hydrolysis through to amino-acids. Erepsin 

 cannot begin with original proteins, but takes the derived pro- 

 teins from uncompleted gastric and tr3rptic digestion and com- 

 pletes the hydrolysis to the final stage of amino-acids. 



It has been difficult to determine whether absorption of 

 digested protein food takes place with the final end products 

 only or with the derived proteins as well. The presence of 

 erepsin, which has without doubt an essential action in protein 

 digestion, as supplementing the action of both pepsin and 

 trypsin, would seem to indicate that it is necessary for absorp- 

 tion that protein food be completely hydrolyzed to amino-acids. 

 It has long been considered as a fact, however, that amino- 

 acids alone when fed to animals or when injected into the blood 

 are unable to be used by the animal to synthesize body protein. 

 If, however, a polypeptide nucleus is present, the amino-acids 



