1 072 



PROTEIN METABOLISM 



[PT. Ill 



© Protein in yolU '\ 



^ " M yolk-sacs I 



O » „ liquid part >Rlddle 



® » " solid central core j 



X " " inbracellularyolk) 



Days 

 —I L— J \ \ L_J 



15 16 17 18 19 20 21 



Fig. 308. 



The subsequent fate of the ovomucoid fraction and the part 

 played by it in metaboHsm have been discussed in Section 8, Here, 

 however, it may be noted that 

 the ovomucoid is not absorbed 

 by the embryonic vessels at a 

 different rate from the ovoalbu- 

 men. This was demonstrated by 

 By waters' experiments, a graph -g 

 of which is given in Fig. 306. The S 

 ratio of the coagulable to the "S 

 uncoagulable protein nitrogen ^" 

 remains the same throughout \ 

 development, though in some •; 

 cases Bywaters' points are rather » 

 erratic, and there may well be 1 2° 

 some interesting relations hidden 

 under this approximation (see L...L 

 also Fig. 307). 



Other points also emerge from 

 Table 135. Sznerovna's figures illustrate the transfer of nitrogen from 

 yolk and white to embryo, the embryo having at the end about as much 

 nitrogen as the yolk had at the beginning. Iljin's figures illustrate 

 the large increase (perhaps due 

 to ovomucoid) in the unpre- 

 cipitable nitrogen of the yolk 

 towards the end of development. 

 But more illuminating are the 

 figures of Riddle represented 

 graphically in Fig. 308, for they 

 show that, in per cent, of the 

 dry solids in the yolk, the yolk- 

 proteins rise during the last 5 or 

 6 days of incubation. This is due 

 to a preference on the part of 

 the embryo for lipoids and fats, ^'^' 3°9' 



the concentration of which correspondingly rapidly decreases, and 

 the graph has only to be compared with that in Fig. 252, where the 

 absorption intensity of the embryo at different times is given, to 

 show how good the correlation is. For 5 or 6 days before hatching 



Days->-5 



