308 PHYSIOLOGY OF ALIMENTATION. 



might readily be explained. The presence of such ferments 

 as alkali-pro teinase (trypsin) has been demonstrated not 

 only in these cells but in practically every cell and fluid of 

 the body. 



A second reason why the products of proteolysis prote- 

 oses, peptones, or amino-acids do not appear in the blood 

 leaving the intestine may reside in the fact that they are in 

 their passage through the intestinal wall broken into yet 

 simpler substances. The proteinase and protease present 

 in the cells of the mucosa may well continue their work until 

 none of the higher polypeptides are left. But, even if all the 

 protein is first split into the simple mono- and diamino-acids 

 before passing into the blood, as seems to be the case, all these 

 acids need not necessarily go to build up albumins and glob- 

 ulins once more. They may be broken into yet simpler 

 substances. There exist in the mucous membrane of the 

 alimentary tract and in various organs in the body ferments 

 which are capable of bringing about such a destruction of 

 mono- and diamino-acids. With one such ferment we are 

 acquainted, through KOSSEL and DAKIN'S work on arginase, 

 which is a ferment capable of acting upon arginin and split- 

 ting this into urea and ornithin. The discovery of this fer- 

 ment, as also the well-known fact that the excretion of urea 

 in the urine reaches its maximum shortly after the consump- 

 tion of a protein meal, seems to indicate that a portion, at 

 least, of the albuminous bodies which constitute our food are 

 rapidly broken up into the vltimate products of protein met- 

 abolism. Apparently, therefore, a part of the protein we ab- 

 sorb goes to maintain the proportion of albumin and globulin 

 found in the blood, and so is distributed to the cells and tissues 

 of the body, while another serves as a source of energy and 

 leaves the body in the form of urea. 



This is perhaps the best place in which to discuss the 

 physiological importance of protease (erepsin) as a digestive 

 enzyme, and of importance, in consequence, in the absorption 

 of the proteins. It is evident that from the nature of its action 



