30 THE AMINO ACIDS 



ARE AMINO ACIDS FORMED DURING GASTRIC DIGESTION 

 OF PROTEIN? 



Protein digestion is initiated in the stomach through 

 the action of gastric juice the active constituents 

 being pepsin and hydrochloric acid. In investigating 

 the nature and extent of gastric digestion three general 

 methods have been employed as follows: (1) the 

 stomach tube method, the only procedure applicable to 

 man, whereby the stomach contents are withdrawn at 

 intervals after a meal, (2) animals fed definite diets 

 are quickly killed at varying periods of time and the 

 stomach contents examined ; or animals are killed with 

 the stomach empty, food introduced and analyzed at 

 intervals, (3) the polyfistulous method fistulas being 

 inserted in the stomach and at various points in the 

 intestine, the food products being withdrawn through 

 these openings. 



What products are formed in the stomach under the 

 influence of peptic digestion? It is self-evident that 

 experiments carried out under artificial conditions, as 

 in beakers, can afford no positive assurance that the 

 products are identical with those formed in the stom- 

 ach. Kiihne was the first to demonstrate that pepsin 

 digestion in vitro leads only to the formation of pro- 

 teoses and peptones. On the other hand, numerous 

 recent investigations have shown by the polyfistulous 

 method that under normal conditions also proteoses and 

 peptones represent the final stages in gastric digestion 

 of protein. All the protein does not of necessity reach 



