02 DIGESTION 



ferment, lipase or steapsin; (4) possibly a milk-curdling 

 ferment. The curdling effect may be due to trypsin. 



Trypsinogen has no action on proteins until, as a result 

 of the action of enterokinase of the intestinal mucosa, it is 

 changed to active trypsin. Enterokinase activates the tryp- 

 sinogen. It then acts more energetically than the pepsin- 

 hydrochloric acid. The earlier stages in the breaking up of 

 proteins are rapidly passed over and peptones quickly con- 

 verted to amino-acids and related bodies. These end-products 

 may be briefly classified as follows: (1) Ammonia; (2) cystin; 

 (3) derivatives of the aliphatic series glycocoll, alanin, serin, 

 leucin; (4) dibasic acids aspartic and glutaminic acids; (5) 

 carboxylic derivatives tyrosin and phenylalanin; (6) pyrro- 

 lidin derivatives prolin, tryptophan; (7) hexone bases 

 lysin, histidin, arginin. The splitting up of proteins under 

 trypsin is more complete after the normal preliminary peptic 

 digestion, but not so complete as the breaking up which occurs 

 on boiling with hydrochloric acid. In each case the change is 

 one of hydrolysis. There is no reason for believing that the 

 intermediary, primary, and secondary proteoses, peptones, etc., 

 are not alike in gastric and pancreatic hydrolysis. 



The amylopsin of the pancreatic juice is identical in its 

 action to the ptyalin of the saliva it changes starch to maltose 

 and dextrins but with greater energy. 



Lipase splits neutral fats into glycerin and corresponding 

 fatty acids. The latter combine with alkalies of the pancreatic 

 juice to form soaps. In this, process the bile is intimately 

 associated; the bile acids and lecithin acting as coferments. 

 It was formerly thought that only a portion of the fat was 

 thus changed, and that the fatty acid was united to some of 

 the bases present in the pancreatic juice, forming a soap and 

 emulsifying the remainder of the fat, which was then absorbed 

 as fine globules. Recently another view has become promi- 

 nent, which supposes all the fat to be converted into soluble 

 glycerin and fatty acids, which are absorbed as such and later 

 recombined as neutral fats in a fine state of emulsion called 

 molecular fat. 



Bile. The bile is partly an excretion and partly a secre- 

 tion. The quantity formed a day in man is from 500 to 

 800 c.c. It consists of water, salts, bile pigments, bile acids, 



