I2i8 METABOLISM OF LIPOIDS, STEROLS, [pt. iii 



free choline never reaches more than 3 mgm. in the whole egg by the 

 end of development, whereas according to Okada it reaches at least 

 75 mgm., and according to Sharpe at least 15. It is difficult to see 

 to what these large discrepancies can be due, but it is probable that 

 the colorimetric method used by the other observers may be less 

 satisfactory than the gravimetric one used by Nakamura. If, how- 

 ever, we are to accept Nakamura's figures as the best, we have to 

 take seriously the initial rise which he found in the total choline, 

 and neither he nor anyone else has been able to suggest anything to 

 explain it. The egg-white and 

 the amniotic and allantoic ^eoo 

 liquids were worked up for .J , 

 choline by Nakamura, but he -g 

 never succeeded in finding 2 

 any there. Fig. 388, which ^ 

 gives his results in per cent. ^' 

 wet weight of the yolk and the f 

 embryo, seems to show that, 

 whereas the free choline of the 

 yolk has large fluctuations, ^ 

 that of the embryo remains at J 

 a constant figure, and that the -g 

 total choline declines in the S 

 yolk and rises in the embryo. !!^ 

 Nakamura made no specula- g 

 tions as to the fate of the 65 f 

 mgm. of combined choline 

 lost from the egg during its de- 

 velopment, except to suggest 

 that it might provide the creatinine of the embryo. We have seen, 

 however, in Section i o that the highest estimate of the creatine or total 

 creatinine content of the embryo by the time of hatching is 25 mgm., 

 so here also there is some discrepancy. 



12-4. The Metabolism of Sterols during Avian Development 

 We can now pass to the cholesterol metabolism of the egg. This 

 substance was prepared from the yolk by Lecanu in 1829, and studied 

 by Gobley in 1846 (see Plate XII). In 191 2 Hanes, while working 

 with a chick embryo of 19 days' incubation, was attracted by the 



Days -^ 5 



Fig. 



