SECT. lo] THE NITROGENOUS EXTRACTIVES 



1149 



lembranes (Fridericia) 



" (LeBrebon^Schaeffer)/ 



(Targonski) 

 " ( Sagara) 







examined by LeBreton & Schaeffer, who made a critical study of 

 the possible methods, and eventually used their own modifications of 

 the Kruger-Schittenhelm method. Their programme involved the 

 estimation of the total nitrogen 



and the purine nitrogen at "I" Purine-nitrogen 



different stages in several series 

 of embryos. Their data on the 

 total nitrogen of the chick have 

 already been given in Table 

 136 of Section 9-3, and their 

 findings with regard to its in- 

 crease in purine bases are shown 

 in Fig, 346. 



Targonski calculated the re- 

 lation between the "anabolic" 

 and the "catabolic" purines, 

 in order to see how much purine 

 nitrogen out of the total made 



Days-*- 5 



Fig. 346. 



The ratio was, he concluded rather curiously, a constant, and meant 

 that about 30 per cent, of the purine nitrogen formed on any one 

 day is catabolic and 60 per cent, anabolic. In view of the considerable 

 differences which have already been noted between the absolute 

 values of different workers for uric acid production, it is difficult 

 to decide whether these relations have any significance. Moreover, 

 wet weight is obviously less satisfactory than dry weight for such a 

 comparison. I therefore recalculated what may be called Targonski 's 

 ratio, using Murray's figures for dry weight, those of Fridericia and 

 of LeBreton & Schaeffer for purine nitrogen, and my own for uric 

 acid production. The justification for this is that all these investigators 



