CHAPTER VIII. 



THE ACTION OF THE ENZYMES FOUND IN THE HUMAN 

 ALIMENTARY TRACT (Concluded}. 



10. Protease (erepsin). The observation of SALVIOLI, HOF- 

 MEISTER, NEUMEISTER, and others that peptone solutions when 

 brought in contact with pieces of still living intestinal mucous 

 membrane no longer give a biuret reaction after the lapse of 

 some time, that is, disappear, has usually been interpreted 

 as evidence indicating that the small intestine has the power 

 of synthesizing protein from the products of protein digestion. 

 It has, in other words, been generally believed that the 

 peptones which are formed in the course of ordinary 

 digestion are built up again into more complex bodies those 

 giving no biuret reaction in their passage through the 

 intestinal wall. Within recent years COHNHEIM l has re- 

 peated some of these older experiments, but in attempting 

 to find corroborative evidence for the ord/nary explanation 

 by the discovery of a larger amount of coagulable protein 

 in the intestinal wall or its surrounding liquids after the biuret 

 reaction had disappeared from the peptone solution than 

 before, his endeavors proved unsuccessful. He found instead 

 that in place of an increase in the amount of coagulable 

 protein he really got an increase in the amount of crystalline 

 digestion-products as the biuret reaction disappeared. The 

 peptones which are formed in the course of ordinary diges- 

 tion when in contact with the living intestinal mucosa there- 



1 COHNHEIM: Zeitschr. f. physiol. Chemie, 1901, XXXIII, p. 451; 

 1902, XXXV, p. 134. 



146 



