34 THE AMINO ACIDS 



formation was shown to be enzymatic in nature and to 

 the enzyme Cohnheim gave the name erepsin. Later 

 investigators showed that erepsin is quite specific in 

 its action it has no influence upon native proteins 

 with the exception of casein and gelatin but is capable 

 of completely transforming proteoses and peptones into 

 amino acids, such as leucine, tyrosine, lysine, histidine, 

 and arginine. In intestinal digestion, therefore, two 

 agencies are to be considered in protein disintegration, 

 namely, trypsin and erepsin. From these two differ- 

 ent types of activity one may perhaps draw the con- 

 clusion that there is a purposeful function for each. 

 It may be imagined for instance that trypsin may per- 

 form a twofold function, the degradation of the 

 protein molecule which may have escaped gastric diges- 

 tion to the proteose or peptone stage, or completely to 

 amino acids. Erepsin on the other hand is present to 

 guarantee that all complicated structures as proteoses, 

 peptones, or polypeptides are reduced to their simplest 

 terms. It is apparent, therefore, from the distribution 

 of enzymes in the intestinal tract that there is a natural 

 provision for ingested protein to be subjected to a 

 series of hydrolytic cleavages whereby only relatively 

 simple amino acids are finally present. 



Although it was generally admitted that protein di- 

 gestion may proceed to the stage of amino acids it was 

 exceedingly difficult to prove the fact when applied 

 to the alimentary tract under normal conditions. The 

 difficulty was twofold in nature. In the first place, 

 demolition of the protein molecule is not of the nature 



