SECT. 10] THE NITROGENOUS EXTRACTIVES 



1153 



result of LeBreton & Schaeffer for the chick are shown in Fig. 348, 

 from which it again appears that the chemical N.P.R. falls during 

 development. Since Fridericia collected the same facts, it is possible 

 to calculate a chemical N.P.R, from his figures, and Fig. 349 shows 

 that a notable fall occurs in his data too. 



LeBreton & Schaeffer also investigated the N.P.R. of the pig 

 and the mouse (Fig. 351). They both descend in the same way as 

 that for the chick. LeBreton & Schaeffer laid some stress, possibly 



Chemical nucleo-plasmabic rabio 



^ £ 



® Fridericia 



• LeBrebonScSchaeffer 



(Fridericia used 

 embryo + membranes 

 for purine -nitrogen 

 and embryo alone for 

 total nitrogen) 



Days ^5 



1.0 15 



Fig- 349- 



2600 

 2400 

 2200 

 2000 

 1800 

 1600 

 1400 

 1200 

 1000 

 800 

 600 

 400 

 200 



10 15 

 Fig. 350. 



not quite justifiably, on the absolute value of the N.P.R. at the 

 earliest stage, interpreting the fact that it fell from 1 2 in the case of 

 the chick, and only from 7 in the case of the pig, to mean that the 

 former was the seat of more intense transformations than the latter. 

 In other words, they introduced a conception of potential, and 

 suggested that perhaps differences in gestation time and life-span 

 might be due to such differences, the chick, as it were, being 

 suspended at a higher initial level than the pig, and correspond- 

 ingly falling more rapidly to equilibrium. The forms of the curves 

 led them to suggest that probably the most rapid fall would always 

 be associated with the highest initial values: thus the chick's N.P.R. 



