98o ENERGETICS AND ENERGY-SOURCES [pt. iii 



differences between the raw materials and the embryo itself, so that 

 not only is the balance between carbohydrate and protein changing 

 through development, but also the balance of integral portions of the 

 carbohydrate fraction. Nevertheless it is interesting that the rough 

 calculation of Table 125 does confirm the conception of an increasing 

 similarity between the embryo and its raw materials with age, and it 

 would be extremely valuable to collect data for a profounder examina- 

 tion of the problem not only in the chick but in many different animals. 



It may be noted also that, if the embryo continued to behave as 

 wastefully all through incubation as it does in the beginning, there 

 would not be nearly enough energy in the egg to provide for it, 

 unless the egg were increased to about twice its present size. Even 

 then there would be no reserve yolk at hatching. 



Since the A.E.E, rises with age, it resembles the percentage of 

 total solids, the percentage of fat, the latent period of growth in 

 tissue culture fragments, the total metabolism and the rate of the 

 heart beat; a miscellaneous collection of factors. But, having Murray's 

 rule in mind, and remembering that embryonic development is 

 symmetrically diphasic in character, we may enquire whether it 

 moves rapidly at first, then slowly, like the growth-rate, or slowly 

 at first, then rapidly, like the metabolic rate. Evidently the rise in 

 A.E.E. resembles the fall in metabolic rate. Thus it would seem as 

 if the furious intensity of combustion with which the embryo begins 

 its life was associated with great wastefulness, while later on greater 

 economy would accompany greater frugality. The calorific value of 

 the embryonic tissue also rises during development, and Murray's 

 graph (Fig. 256) shows that it goes up in a curve shaped rather like 

 that for the A.E.E. Thus the richer in potential energy the embryonic 

 body becomes per unit weight, the more efficient is the transfer of 

 energy from the yolk and white. 



Though the curves for P.E.C. and A.E.E. are different, it is inter- 

 esting to find that the average P.E.C. for all development is o-68, 

 while the average A.E.E. is 66 per cent. Out of 100 gm. of solid 

 presented to it, the embryo can store 68; out of 100 cal. presented to 

 it, the embryo can store 66. 



The conclusion that the A.E.E. of the chick embryo increases with 

 age, and that, in the early stages of development, storage of energy 

 is very inefficient, is in agreement with the views of Armsby. That it 

 rises, as we have seen, to approximately 70 per cent, at hatching, is 



