PROTEIN METABOLISM 87 



that is the fact of the rapidity with which large quan- 

 tities of protein are catabolized in the body. In a few 

 hours great quantities of protein may be disintegrated 

 as judged by the corresponding increase in urinary 

 nitrogen. It is hardly probable that living protoplasm 

 could be synthesized so rapidly and so much of it be 

 so quickly destroyed again. This is the more incredi- 

 ble since the same fact applies irrespective of the 

 previous state of nutrition of the organism. 



In 1905 Folin subjected the experiments of Schon- 

 dorff to a searching criticism and pointed out that the 

 evidence furnished by them was by no means unassail- 

 able. Upon studying the details of one of SchondorfFs 

 experiments, Folin found that the actual increase in 

 urea nitrogen in the transfused blood amounted to less 

 than one-tenth of 1 per cent instead of 125 per cent as 

 calculated by Schondorff. "Considering the numerous 

 sources of error and uncertainty necessarily attached 

 to an experiment of this kind, it seems very strange 

 that the extraction of 25 mgm. of urea-nitrogen from 

 the hind limbs of a dog killed while engaged in digest- 

 ing 700 gm. of meat should be accepted as proving not 

 only that protein catabolism did occur during the 

 experiment, but also that it occurred in the bioplasm 

 and not in the circulating protein." 



No direct evidence has been obtained to prove or dis- 

 prove the one or the other of these last two widely 

 divergent theories. The distinction between tissue 

 protein and food protein is probably one of degree 

 rather than of kind. 



