SECT. 9] 



PROTEIN METABOLISM 



1093 



Among the investigators who have estimated the uric acid pro- 

 duced by the chick embryo there is some divergence in the absolute 

 magnitude of their values. 

 Table 141 illustrates this, and ,: 

 shows that Fridericia's results, 

 for instance, though at first ^ 

 of exactly the same order as J 

 mine, draw off about the S 

 15th day, and rise much o'^ 

 higher during the remaining ^ 

 time. Fiske & Boyden's, on "f- 

 the contrary, are always 5 

 higher than either Fride- ^ ^ 

 ricia's or mine, while Kamei's ^ 

 are the lowest of all. Tar- |, 

 gonski embodied his results ^ 

 in singularly confusing and 

 obscure tables, but the uric 

 acid production of his em- 

 bryos can be calculated from 



O Fiske &;,Boyden 

 © Needham 



Days 



Fig. 329. 



them, with the result that his data confirm mine, none of his points 



being very far away from the curve of Fig. 328. These are all the sets of 



figures for uric acid production 



which we have at present, and, 



until a thorough comparative 



assessment is made of the effect 



of breed, etc., on uric acid pro 



duction, the differences will 



remain difficult to account 



for^. But it is important that 



the peak in nitrogen cata- 



bolism emerges from at least 



two of them, and it may be 



supposed that this is due to a 



relative rather than a uni- 



Fig. 330. 



versal validity inhering in each series. This is illustrated by Fig. 329. 



1 Differences of technique may account for much divergence; thus some methods 

 estimate ergothioneine as well as uric acid. Calvery's later figures for uric acid agree 

 exactly with those of Needham. 



