1074 



PROTEIN METABOLISM 



[PT. Ill 



Fig. 311. 



with a few later figures of Nakamura, which are not concordant. 

 Concentrating attention on Fig. 311 for the moment, it can be seen 

 that the wet weight curve, after a peak on the 6th day and a depres- 

 sion on the gth, gains a plateau 

 and remains there for the rest of 

 development. The dry weight 

 curve presents the same peak 

 and the same depression, but, 

 since the embryo is growing 

 much drier as it increases in 

 size, the dry weight curve drops 

 away steadily after the loth 

 day. It is significant that there 

 is a very vigorous period of pro- 

 tein absorption^ before the 5th 

 day, and another from the 

 14th to the 1 8th days. The depression in the curves of Fig. 311 comes 

 just between the two maxima of protein absorption. The amount 

 of non-protein nitrogen in 100 gm. of embryo is related, then, to the 

 amount of protein nitrogen which 100 gm. of embryo is receiving 

 from the rest of the egg. Reference 

 to Fig. 250 illustrates this. 



Another curve which is worth 

 studying is the curve for non- 

 protein nitrogen in percentage of 

 the total nitrogen (Table 136 and 

 Fig. 312). Low at first, the value 

 rises to attain a peak on the Gth 

 day, and thereafter falls, except 

 for a slight oscillation about the 

 gth day, probably comparable in 

 cause with those noted as occurring 



at the same time in the curves for Fig, 312. 



non-protein nitrogen as percent- 

 ages of wet and dry weight. It may be said, then, that, though little 

 change seems to take place in the non-protein nitrogen outside the 

 embryo, yet, inside it, definite peaks are found, and that these corre- 

 spond with the periods of greatest intensity of protein absorption, such 



1 This does not, of course, mean absorption of intact protein; see pp. 920 ff. 



