CHAPTER II 



DIGESTION, AND BACTERIAL ACTIVITY IN 

 RELATION TO THE AMINO ACIDS 



Concerning the nature of protein digestion Schaefer 

 in 1898 wrote : "The products found toward the end of 

 a proteid digestion in vitro are distinguished from the 

 proteids from which they originate by being slightly 

 diffusible. To this fact great importance was at one 

 time attributed, because it was thought that only pro- 

 teids in a diffusible form were capable of absorption, 

 and hence that peptonization was in all cases a neces- 

 sary preliminary. It is now generally admitted that 

 many forms of native proteid are capable of entering 

 the epithelial cells (of the intestine) without previous 

 change by digestion or otherwise ; and in those cases in 

 which a proteid is incapable of direct absorption a 

 much less profound change than peptonization is suffi- 

 cient to render it so, namely, conversion into acid or 

 alkali albumin." With regard to the extent of amino 

 acid formation in digestion Schaefer says: "It is not 

 known with certainty to what extent amino acids are 

 formed from proteids, in the natural course of intes- 

 tinal digestion. The experimental evidence is some- 

 what conflicting, but the majority of observers are of 

 the opinion that but little proteid is absorbed as leucine 

 or tyrosine, being nearly all absorbed as albumose or 



