SECTION 10 



THE METABOLISM OF NUCLEIN AND THE 

 NITROGENOUS EXTRACTIVES 



Sendj 



Purine bases 

 ® Embryo) 

 O White lc„„H-,,. 

 • Yolk /Sendju 



©Whole J 



^ Whole,chick] Mendel 80 

 ^ Whole, duck j Leavenworth 

 H WholeXFridericia) 



10- 1. Nuclein Metabolism of the Chick Embryo 



It has already been recounted in Section i (see p. 336) that many 

 investigators, following Kossel, have not been able to isolate any 

 purine bases from the unincu- 

 bated hen's egg. At the present 

 time it is generally agreed that 

 not more than 2 per cent, of the 

 total nitrogen at the beginning 

 of development is in the form 

 of purine bases. All investigators 

 have agreed, moreover, that by 

 the end of development purine 

 bases are present in the embryo 

 in considerable quantity, and 

 there is no doubt that, during the 

 embryonic growth of the chick, 

 purine bases are synthesised. The 

 only dissentient voice which 

 breaks this unanimity is that of 

 Mesernitzki, who maintained in 

 1903 that as much purine (esti- 

 mated as xanthine) was present 

 in the egg at the beginning as in 

 the embryo at the end, but we 

 may disregard it, for Fridericia 



Days 



Fig- 343- 



adversely criticised his technique, and repeated his experiment with 

 contrary results. 



Sendju's paper contains figures for the purine nitrogen in white, 

 yolk and embryo, and is probably the best one with which to intro- 

 duce the subject. As is evident from Fig. 343, there is never more 

 than a minimal quantity of the bases in the egg-white, but in the 

 yolk, on the contrary, there is a good deal, and on the 14th day it 



