792 PHYSIOLOGY OF DIGESTION AND SECRETION. 



intestinal mucosa. The action of this latter enzyme is exerted 

 especially upon the albumoses and peptones, breaking them down 

 into the amino-acids, so that apparently whatever peptone or 

 albumose may escape the final action of the trypsin before absorp- 

 tion is likely to be acted upon by the erepsin before reaching the 

 blood.* Another possible view is that suggested by Abderhalden. f 

 According to this author, the hydrolysis of the protein by pepsin, 

 trypsin, and erepsin is not necessarily complete. Some amino- 

 bodies, such as tyrosin, leucin, arginin, etc., are split off from the 

 protein molecule, but there may remain behind what one may 

 call a nucleus of the original molecule, which serves as the starting- 

 point for a synthesis. This nucleus is a substance or a number of 

 substances intermediate between the peptone and the simpler 

 end-products, and is spoken of as a peptid or polypeptid (see 

 Appendix). It has been shown that in tryptic digestion such sub- 

 stances are formed — that is, substances which are not peptones, 

 since they no longer give the biuret reaction, but which have a 

 certain complexity of structure, since upon hydrolysis with acids 

 they split into a number of amino-acids. But bearing in mind 

 the fact that the action of the trypsin is normally combined with 

 or is supplemented by that of the erepsin, it seems probable that in 

 digestion in the body the protein molecule is broken down com- 

 pletely to its building-stones. The value of this complete splitting 

 of the protein of the food lies in the possibility that thereby the 

 body is able to construct its own peculiar type of protein. Many 

 different kinds of proteins are taken as food, and many of them if 

 introduced directly into the blood act as foreign material incapable 

 of nourishing the tissues. If these proteins are broken down more 

 or less completely during digestion, the tissue cells may reconstruct 

 from the pieces or building-stones a form of protein adaptable to 

 their needs, and more or less characteristic for that particular 

 organism. Just as the letters of the alphabet may be combined 

 in different ways to make different words, so the various amino- 

 acids may be combined to make proteins of many different kinds. 

 Action of the Diastatic Enzyme (Amylase) of the Pancre- 

 atic Secretion. — This enzyme is found in the secretion of the 

 pancreas or it may be extracted from the gland. Its action 

 upon starchy foods is similar to or identical with that of ptyalin. 

 It causes an hydrolysis of the starch with the production finally of 

 maltose and achroodextrin. Before absorption these substances are 

 further acted upon by the maltase of the intestinal secretion and 



* Vernon ("Journal of Physiology," 30, 330, 1904) believes that the 

 pancreatic secretion contains two proteolytic enzymes — trypsin proper, 

 which converts the proteins to peptones, and pancreatic erepsin, which breaks 

 up the peptones into the simpler end-products, the amino-bodies. 



t Abderhalden, loc. cit. 



