ALBUMINS OR PROTEINS. 209 



Cohnheim, 1 that the breaking down of the proteins in the intestine was 

 more extensive than was originally thought. The former succeeded in 

 isolating crystalline cleavage-products from the intestinal contents of dogs 

 which had been fed on a diet rich in albumin, the animals being killed 

 at varying times, for instance, at intervals of six hours. 



The discovery of O. Cohnheim, that the mucous membrane of the 

 intestine contains a ferment, erepsin, which further disintegrates the pep- 

 tones, casts doubt upon the conclusions drawn from the above-men- 

 tioned experiments of F. Hofmeister and Salvioli. 



Recent investigations, from various standpoints, indicate a considerable 

 disintegration of the albumin molecule. It has been shown for one thing 

 that intestinal digestion is very similar to that artificially produced by tryp- 

 sin. Amino acids, e.g., tyrosine, leucine, alanine, glutamic acid, aspartic 

 acid, lysine, arginine, and histidine, are formed in the intestinal canal and 

 even the polypeptides which are observed in artificial digestion with 

 trypsin, and are attacked with difficulty, if at all, by ferments. It is at 

 present uncertain as to how far the disintegration goes in individual cases, 

 as to whether polypeptides with a small number of amino acids result, or 

 that the digestion stops while the chains are more complicated. We 

 have already shown that we can draw no conclusion as to the extent 

 of the decomposition simply on account of the appearance of free 

 amino acids. More complex substances may be present at the same 

 time. 



We have reached a like conclusion concerning the decomposition of the 

 proteins in the intestinal tract from another standpoint. 2 The significance 

 of the function of digestion is not merely to prepare the food for absorption. 

 It goes far beyond this point. The separate components of the food are 

 not in a condition suitable for the economy of individual beings. Every 

 species of animal in fact, every individual has its own specifically 

 constituted tissues and cells. If the diet were always the same, the for- 

 mation of the tissues might bear some close relation to the components 

 of the food. The diet varies, however, and, especially in the case of 

 human beings and the omnivora, is exceedingly diverse in nature. In 

 order to maintain the individuality of the animal, and to make its 

 organism independent of the outer world in the matter of food taken, it 

 disintegrates the nutrient it receives, and utilizes those components which 

 may be of service to it in building up new complexes. This conception 

 of the process of digestion, as a whole, will become especially clear when 

 we consider the most important food of growing mammals, i.e., milk. 



1 Ibid. 33, 451 (1901). 



2 Emil Abderhalden: Z. physiol. Chem. 44, 17 (1905); Zent. Stoffwechs.-Verdau- 

 ungs-Krank. 6, 647 (1904); Med. Klinik. 1, Nr. 1 and 2 (1905); 1, Nr. 46 and 47 

 (1905). 



