THE PROTEINS AND THEIR METABOLISM 



123 



rium. Gelatin was found to be one of these. No matter how mucli gela- 

 tin was administered to an animal, the animal would still continue to 

 burn some of its own protein in addition. Krummacher (ISDfSa) went so 

 far as to administer all of the animal's caloric requirements in the form of 

 gelatin, but was not able to obtain nitrogenous equilibrium. 4 Various the- 

 ories were advanced which were supposed to explain the reasons for this. 

 Kauffinun, in 1005, conceived the idea that the explanation mav be found 

 in the fact that gelatin lacks certain amino acids which may be indispens- 

 able to the animal organism. These are tryptnphan, tyrosin and cystin. 

 He therefore added small amounts of the.^e to gelatin, carried out a series 

 of experiments on man and dog^nd found that nitrogenous equilibrium 

 could be maintained under those circumstances. Abderhalden confirmed 

 the experiments and went a step further. He took casein, digested it to 

 the amino acid stage, and fed it to a dog for a period of seven days. Dur- 

 ing those seven days the dog gained 20.0 grams in weight and retained 

 0.12 gram of nitrogen per day. (See Table VIII, Section II.) During 

 the succeeding six days the animal was given a corresponding amount 

 of casein digest minus tryptophan. The animal lost 250.0 grams in body 

 weight and lost nitrogen to the extent of 0.83 gram per day or 

 5.0 grams for the period of six days. " (See Table VIII, Section IIT.) 

 During the succeeding six days the animal was put back on its original 

 diet. It regained 100.0 grams in weight and on the fourth day established 

 nitrogenous equilibrium. 



TABLE VIII 

 ABDEBHALDEN'S EXPERIMENTS 



DOG WAS FED 22 GRAMS OF PKKDIGESTED DOG MEAT. EXPERIMENT SHOWS THAT NITROGEN- 

 OUS EQUILIBRIUM A_ND BODY WEIGHT CAN BE MAINTAINED ON IT 



4 For complete review of literature see Murlin, J. R., American Journal of Physi- 

 ology, 1907, vol. 19, p. 285 and 1007, vol. 20, p. 234. 



