DIGESTION AND RESORPTION 99 



of opinion is that, as a matter of fact, proteins are largely re- 

 sorbed in the form of comparatively simple cleavage products ; 

 not necessarily in every case as simple amino acids but at least 

 in the form of comparatively simple peptids. 



The nucleic acids derived from the peptic or tryptic diges- 

 tion of the nucleoproteins are split by the nucleases of the in- 

 testinal juice into mononucleotids and these again by the 

 nucleotidases of the same secretion into nucleosids (53). No 

 digestive enzyms attacking the latter class of compounds are 

 known, but they are split to some extent by intestinal bacteria 

 into pentoses and purin or pyrimidin bases. Furthermore, it has 

 been found that extracts of the intestinal mucous membrane 

 (epithelial cells) possess the power of bringing about the same 

 cleavages which are accomplished by the enzyms of the in- 

 testinal juice, and in addition are able to split the resulting 

 nucleosids into pentose and base. It appears, then, that the 

 final digestive products of the nucleic acids are, as in the case 

 of the simple proteins, relatively simple substances, viz., phos- 

 phoric acid, pentoses, and purin and pyrimidin bases. 



140. Putrefaction of proteins. Attention has already been 

 called, in connection with the digestion of the carbohydrates, 

 to the bacterial flora of the digestive tract. The carbohy- 

 drates, as was shown, are acted upon chiefly by the organisms 

 producing the methane fermentation. Proteins and their de- 

 rivatives, on the other hand, have been shown by Kellner to 

 contribute practically nothing to this fermentation in the case 

 of cattle. They are, however, especially subject to the action 

 of the organisms producing putrefaction. The action of such 

 organisms is prevented in the stomach by the hydrochloric acid 

 of the gastric juice. In the small intestine they become more 

 active, especially as the feed reaches the lower portion, while 

 their activity lessens again as the lower portion of the large in- 

 testine is reached, owing to the progressive resorption of water 

 from the intestinal contents. The characteristic products of 

 the putrefaction are ammonia and certain aromatic compounds 

 derived from the heterocyclic components of the proteins (47). 



The aromatic products of putrefaction (indols and phenols) 

 are found in part in the feces but are in large part resorbed. 

 They cannot, however, be utilized by the organism but, on the 

 contrary, are poisonous and are therefore combined with other 



