THE ABSORPTION OF PROTEINS 53 



was treated as so much waste material being eliminated 

 by the kidneys. Moreover, he also failed to find any 

 trace of peptone in the blood or lymph of animals at 

 the height of digestion. 



The experiments cited above failed to throw any 

 light upon the fate of the peptone, beyond its dis- 

 appearance. In later experiments Neumeister showed 

 the presence of leucine and tyrosine in the intestine 

 after introduction of peptone, thus indicating a further 

 decomposition of the peptone. Even though it might 

 be accepted that peptone placed in the intestine under- 

 goes a further, breakdown to amino acids there still 

 existed no proof that the amino acids were absorbed 

 as such. It is possible to assume a synthesis of the 

 amino acids back into protein in the act of absorption 

 through the intestinal wall. An example of sjuch a 

 reaction is found in the digestion of fat where fat is 

 split into fatty acids or soap and glycerol and regener- 

 ated as fat during the process of absorption. 



It was Cohnheim's attempt to isolate this hypotheti- 

 cal protein from the intestinal wall which led to his 

 discovery of the enzyme erepsin already considered the 

 action of which has had a tendency toward filling in 

 some of the gaps in our conception of the nature of 

 intestinal digestion and absorption. Although it had 

 been recognized for many years that amino acids are 

 formed in intestinal digestion they were regarded as 

 by-products and quite unimportant. As a result of 

 the discovery of erepsin the purpose of the formation 

 of amino acids first received its due recognition. 



