142 PHYSIOLOGICAL CHEMISTRY 



longer tenable. From the investigations of numerous observers we 

 have learned that artificial gastric digestion if permitted to proceed for a 

 sufficiently long period will yield, in addition to proteoses, peptones and 

 peptides, a long list of protein cleavage products which are crystalline 

 in character, including leucine, tyrosine, alanine, phenylalanine, aspartic 

 acid, glutamic acid, proline, leucinimide, valine, and lysine. A similar 

 group of substances may result from the action of the enzyme trypsin 

 (see page 1.86) . The relative amounts of proteoses, peptones, and crys- 

 talline substances formed depends to a great extent upon the character 

 of the protein undergoing digestion, e.g., a greater proportion of pro- 

 teoses results from the digestion of fibrin than from the digestion'of 

 coagulated egg-white. We must not be led into the error of thinking 

 that the large number of protein cleavage products just mentioned are 

 formed in the course of normal gastric digestion within the animal 

 organism. They are formed only after comparatively long-continued 

 hydrolysis. In pancreatic digestion, however, there are formed even 

 under normal conditions the large number of cleavage products to 

 which reference has been made. Peptic proteolysis, therefore, within 

 the animal organism differs from tryptic proteolysis (see page 186) 

 in that the former yields larger amounts of proteoses, smaller amounts 

 of peptones and no considerable quantity of crystalline bodies as end- 

 products in the brief period during which proteins are ordinarily sub- 

 jected to gastric digestion. Prolonged hydrolysis with gastric juice 

 does, however, yield considerable quantities of the non-protein end- 

 products. In cases of cancer of the stomach a pep tide-splitting 

 enzyme (erepsin) is said to be present in the stomach contents. This 

 enzyme is believed to be elaborated by the cancer tissue and its identi- 

 fication is of importance in connection with the diagnosis of gastric 

 cancer. The glycyl-trytophane test 1 is sometimes used for this 

 purpose. This test has been very severely criticized (see page 199). 

 Abderhalden and Meyer 2 have shown active pepsin to be present 

 in the contents of all parts of the small intestine. It is suggested that 

 pepsin may be adsorbed in the stomach by such protein substances 

 as pass into the intestine in solid form and that the pepsin thus pro- 

 tected may bring about gastric digestion whenever the reaction of the 

 surrounding intestinal contents is favorable. This fact may be of 

 importance in connection with the profound proteolysis taking place 

 in the intestine. Heretofore, this process was believed to be furthered 

 alone by trypsin and erepsin. The passage of adsorbed pepsin into the 

 intestine may be an efficient aid to the proper digestion of solid proteins 



1 Neubauer and Fischer: Deut. Arch.f. klin. Med., 97, 499, 1909. 



2 Abderhalden and Meyer: Zeit. fur physiol. Chem., 74, 67, 1911. 



