DIGESTION OF THE PROTEINS 



241 



In the first place it has been ascertained, thanks to the researches 

 of London, that during the normal digestion of proteins in the intestine 

 large proportions of amino-acids are actually formed, and progressively 

 absorbed subsequently to their formation. The experiment consisted 

 in establishing a number of fistulae at intervals along the intestinal 

 tract, so that samples of the intestinal contents could be withdrawn 

 and examined after varying periods of intestinal digestion. The 

 animal was fed with measured amounts of pure proteins and the diges- 

 tion-products obtained from the successive sectors of the intestine 

 (Fig. 7). It was found that these samples contained notable amounts 

 of amino-acids and, moreover, that the relative proportions of the 

 amino-acids arising from the dietary protein differed in different sec- 



FIG. 7. Dog with intestinal and glandular fistulse. (After London.) 



tions of the intestine. Thus when the animal received the protein 

 Gliadin. the duodenum contained 0.75 grams of tyrosine to 2.5 grams 

 of glutamic acid; the jejunum contained only 1.1 grams- of tyrosine 

 per 20.9 grams of glutamic acid and the ileum contained only a trace 

 of tyrosine as contrasted with 33 grams of glutamic acid. Evidently 

 therefore, not only are amino-acids formed in the normal intestinal 

 digestion of proteins, but they are absorbed selectively, e. g., in the 

 particular case in point, tyrosine was absorbed from the intestine much 

 more rapidly than glutamic acid. 



In the second place it has been shown by Folin and Denis, that if 



amino-acids are introduced into a loop of intestine the non-protein 



nitrogen of the blood is decidedly increased during the period that 



absorption might be supposed to be occurring, and the origin of this 



16 



