DIGESTION 33 



their rapid formation indirectly by facilitating the 

 action of trypsin. 



INTESTINAL DIGESTION 



Kiihne made the important discovery that there is 

 an essential difference between the digestive action of 

 trypsin and that of pepsin. He stated that the influ- 

 ence of the former does not cease with the formation 

 of peptone but is carried to a stage where crystalline 

 products appear the amino acids. As late as 1900, 

 however, these substances were regarded as by-pro- 

 ducts in natural digestion of little significance and 

 formed in relatively small quantities. At that time the 

 cleavage products recognized were leucine, tyrosine, 

 aspartic acid, glutamic acid, lysine, arginine and histi- 

 dine and proteinochromogen (see Chapter I). With 

 the growth of knowledge concerning protein chemistry 

 most of the characteristic amino acids have since been 

 isolated from intestinal contents. 



In 1906 Cohnheim gave a new meaning to intestinal 

 digestion by his discovery of an enzyme capable of 

 splitting proteoses and peptones into simpler products. 

 Cohnheim was of the opinion that synthesis of protein 

 from peptones occurred in the intestinal wall. While 

 endeavoring to determine this point he noted that the 

 characteristic peptone reaction disappeared. Its dis- 

 appearance was not due to protein synthesis as was 

 early assumed, but because crystalline decomposition 

 products were formed from it. This chemical trans- 



