128 THE AMINO ACIDS 



tions of casein together with sugar. To one series of 

 mice unchanged casein was fed, to a second, casein 

 that had been digested with pancreatin for a period 

 of two months, a third series received casein digested 

 for one month with pepsin-hydrochloric acid and then 

 for two months with pancreatin, the fourth series 

 were fed with casein hydrolyzed for ten hours with 

 25 per cent sulphuric acid. The results showed that 

 those animals fed with casein digested with pancreatin 

 for two months and those given unchanged casein 

 lived about the same length of time. Mice fed on the 

 other two preparations lived shorter periods of time. 

 Other investigators obtained similar results. An 

 interesting controversy now arose as to the reason 

 for the specific difference between products formed 

 by enzymes and those resulting from acid hydrolysis. 

 Abderhalden and Rona from their work cited above 

 put forth the hypothesis that the difference in the 

 two products lay in their content of polypeptides. 

 According to this view digestion by ferments results 

 in the presence of considerable amounts of fairly 

 complex polypeptides which serve as nuclei for the 

 synthesis of new protein material. Hydrolysis by acid, 

 however, carries the digestion beyond the stage of 

 polypeptides, hence, no nuclei for synthesis are present 

 and the inability of acid digestion mixtures to fully 

 serve as nitrogenous pabulum is explained. In sup- 

 port of their hypothesis they offer the observation that 

 the casein preparation formed by pancreatin action 

 contained only 16 per cent of polypeptides, that of the 



