THE PHYSIOLOGY OF PROTEIN METABOLISM 



London, " Handb. d. Biochemie," Oppenheimer III, p. 77. 



According to Tobler (398), on the other hand, from 50 per cent, to 

 5 7 per cent, of the digested product reaches the intestine in the form 

 of peptone, some n per cent, to 14 per cent, in the form of proteoses 

 and from 30 per cent, to 34 percent, in the form of soluble or insoluble 

 protein. Zunz (430) concludes that three-fifths of the nitrogen of the 

 products of protein digestion in the stomach enters the duodenum in a 

 very simple form (mainly peptones) and about two-fifths in the form of 

 proteoses. He is therefore inclined to agree with the work of Tobler. 

 Zunz further shows that the condition in which the food is consumed 

 plays a part in the degree of digestion reached. Thus when a dog is fed 

 with cooked meat there is more proteose present in the stomach con- 

 tents than when the same food (horse flesh or beef) is given raw. He 

 also states that, in certain experiments which he carried out in dogs, 

 where, previous to the digestion experiment, the ducts of the pancreas 

 were ligatured, digestion in the stomach was more complete than when 

 the pancreas was acting freely. He concludes that there may be at 

 times an increased compensatory digestion in the stomach. 



The degree of gastric digestion would not seem to be a matter 

 of very great moment, however, as under normal conditions these 

 changes in the stomach are only preparatory to the action of the 

 pancreatic and intestinal juices. That this preparatory action is of 

 importance, however, is shown by the in vitro experiments of Fischer 

 and Abderhalden (126); they found that tryptic digestion took place 

 much more rapidly and completely when the protein had been pre- 

 viously subjected to the action of pepsin and hydrochloric acid. They 

 found that, if caseinogen were first digested with an artificial gastric 

 juice before digestion with trypsin, they could isolate proline and 

 phenylalanine, whereas if pancreatic digestion of caseinogen were carried 

 out alone, these amino acids were not found in the free state but only in 

 the polypeptide form. The polypeptide compound, however, was not 

 completely decomposed by the double digestion. Acid hydrolysis, on 

 the other hand, breaks up this polypeptide completely, both of the amino 



