SECT. 7] OF EMBRYONIC DEVELOPMENT 983 



pated as heat if the endothermic processes had not caught and held 

 it), on the one hand, and the energy absorbed by the embryo from 

 the raw materials, on the other hand, allowing for the basal metabolic 

 requirements. It thus has to do, not with energy storage as a whole, 

 but with the storage of energy from a particular source, i.e. coupled 

 reactions with one endothermic component^. During the absorption 

 of 100 cal. of energy, 66 will be stored and 33 lost, but only 9, 

 say, out of that 66 will be saved from the loss by the endothermic 

 processes. Rapkine's coefficient may, therefore, be called the S.E.E. 

 (synthetic energetic efficiency). As a concrete example, in the case 

 of the chick, the values as averaged from many observations can be 

 read off from Fig. 259, and the usual fraction for R.E.E. is 



(86.85) - (^6^+ .7 (say)) = ^"^ P" =^"'- 



For the S.E.E. the numerator would at first sight seem to be a minus 

 quantity, for in Murray's work, for instance, the calorific value of 

 I gm. of dry unincubated mixed yolk and white was 6-94 Cal. and 

 that of I gm. of dry finished embryo was 6-2 Cal., so that no increase 

 in specific energy-content would appear to have taken place. How- 

 ever, the finished embryo is not comparable with the unincubated 

 yolk and white, for a notable proportion of the fat in the latter dis- 

 appears by combustion, and some of it is left behind as spare yolk 

 at hatching. The following calculation is therefore required to give 

 the energy value of an amount of yolk and white roughly comparable 

 with the finished embryo : 



The finished embryo of the chick weighs 6*oo gm. dry weight and has in it 37-5 Cal. 



i.e. 6-2 Cal. per gram dry weight. 

 The egg at the beginning of development has inside it 12-45 g™- ^^Y weight and 

 86-85 Cal., i.e. 6-94 Cal. per gram dry weight ... 86-85 Cal. = 100 % 



For combustion 2-5 gm. fat are used, which at 



9-3 Cal. per gram is 23-25 Cal 2325 Cal. = 26-4% 



For yolk unused at the end of development, i.e. 

 about 4-75 gm. dry weight of which 40-5 % is fat 

 and 50 % protein, i.e. : 



For fat ... 17-8 Cal. 



For protein ... 11-4 Cal. 



29-2 Cal. ... ... 29-20 Cal. = 30-4 % 



52-45 Cal. 



86-85 -52-45=34-40 Cal. 



1 It should be noted that this is the only kind of energy-storage which will raise the 

 chemical potential of the embryonic body. 



N E II 63 



