SECT. lo] THE NITROGENOUS EXTRACTIVES 1155 



these in terms of 100 mgm. of purine nitrogen, and obtained the 

 curve shown in Fig. 352. Fridericia's data were also treated in this 

 way, but with quite different results, for, whereas the figures of 

 LeBreton & Schaeffer give a markedly peaked curve at 12 days 

 of development, those of Fridericia give an amorphous assemblage of 

 points. LeBreton & Schaeffer pointed out that his figures included 

 the purines of the membranes, and concluded that when their masking 

 effect was removed by omitting them from the estimations — as they 



Chick 

 ® - membranes( Le Breton ficSchaeffer) 

 " (Fridericia) 



>» a> 



■D ^ 

 o 



membranes (LeBrebon ^Schaeffer) 



(Murray's dry weights) 

 membranes (Fridericia) 



• •mgms. free 

 purine-nitrogen 

 per whole egg 

 (Takahashi) 



Days-* 



Days -^5 



Fig. 352. 



Fig. 353- 



themselves had done — then a clear maximum of intensity of pro- 

 duction of purine bases revealed itself In order to have this important 

 fact in a comparable form with other intensity curves, I recalculated 

 the data in relation to dry weight (figures of Murray), with the 

 result (shown in Fig. 353) that now both Fridericia's and LeBreton 

 & Schaeffer's curves give a clear-cut peak about the 12th day. 

 No one has had any explanation to offer of this peak in purine 

 nitrogen production, but LeBreton & Schaeffer themselves hinted 

 that it might be a curve of the same nature as the increment curve of 

 an autocatalysed monomolecular reaction. They stated that their data 

 for the pig and mouse embryo led to similar peaks. 



