36 THE AMINO ACIDS 



The small intestine, therefore, may be regarded as 

 the seat of profound protein digestion, the products 

 arising being the amino acids typical for hydrolytic 

 cleavage of protein. Undoubtedly all digestible pro- 

 teins are ultimately reduced to the condition of amino 

 acids. From this it follows according to present views 

 that nitrogenous metabolism is concerned mainly with 

 the amino acids and the transformations which they 

 undergo. 



INTESTINAL BACTERIA AND THE AMINO ACIDS 



In the early days of the history of protein digestion 

 great difficulty was experienced in the determination of 

 the actual products formed because of the accompani- 

 ment of putrefaction. This was especially true for 

 tryptic digestion where it is desirable to maintain an 

 alkaline medium, an environment also favorable for 

 bacterial growth. Kuhne was the first to demonstrate 

 the activity of trypsin in the presence of antiseptics 

 and through the employment of antiseptic digestion 

 mixtures a sharp division line was soon drawn between 

 the products of tryptic digestion and those formed by 

 bacterial agencies. 



In general the products of putrefaction are identical 

 whether formed outside the body or within. The type 

 of action is similar to other kinds of digestion activity. 

 Indeed, there is little doubt that the same kind of 

 agencies are at work in the two instances, namely, 

 enzymes. In the one case they are present in a secre- 



