SECT. 6] OF THE EMBRYO 941 



Later work by Schilling & Bleecker afforded further data about the 

 absorption of the spare yolk by the hatched chick. They observed 

 sometimes a curious failure to absorb it; thus in one instance an 

 amount of 4-8 gm. was found when there should, according to the 

 normal curve, only have been 0-021 gm., and in another case 2-95 

 instead of 0-62. Their conclusions differed a good deal from Iljin's, 

 for they found no difference in rate of absorption between well-fed 

 and ill-fed chicks^, nor did the amount of yolk unabsorbed seem to 

 bear any relation to the growth-rate of the individual. 



Romenski, a student of Iljin's, studied the question from another 

 angle, that of nitrogen utilisation, and drew up, as the result of his 

 observations, the following table : 



Gm. 

 37-60 



30-00 



0-499 

 6-951 



Average weight of the chick at hatching 



Average weight of chick minus its spare yolk ... 



Nitrogen content of chick minus spare yolk (i.e. 57-97 % of the 



original store of nitrogen in the egg) ... 

 Average weight of the spare yolk 

 Nitrogen content of the spare yolk (i.e. 32-32 % of the origina 



store of nitrogen in the egg) 

 Average weight of shell, membranes, and excreta 

 Nitrogen content of shell, membranes, and excreta (i.e. 9-55 % 



of the original store of nitrogen in the egg) ... ... ... 0-058 



He then subjected the hatched chicks to 36 hours' starvation or, 

 more strictly speaking, he allowed them no other nourishment than 

 that contained in their yolk-sacs. The results of similar estimations 

 at the end of that time were as follows : 



Gm. 



Average weight of chick after 36 hours (minus its spare yolk)... 33'6o 



Nitrogen content of chick body ... ... ... ... ... 0-534 



Average weight of spare yolk after 36 hours ... ... ... S'^S 



Nitrogen content of spare yolk after 36 hours ... ... ... o-iii 



From these facts it is clear that during the post-hatching period the 

 yolk lost 160 mgm. of nitrogen and the chick's body gained 35 mgm. 

 so the loss by oxidation was 125 mgm. Evidently the original con- 

 tention of Iljin, that the spare yolk is used much more for energy 

 than for storage, received confirmation through the work of Romenski, 

 and the efficiency would here be extremely low, about 20 per cent. 

 Romenski' s figures permit us to compute what intensity of protein 

 combustion goes on under these conditions. The 125 mgm. of nitrogen 



^ Later work by Roberts ; Parker ; Holmes, Halpin & Beach, and Heywang & Jull, 

 agrees with Schilling & Bleecker's view on this point. 



