SECT. 7] OF EMBRYONIC DEVELOPMENT 951 



average figure for the chick was 100 cal. and for the adult hen 71, 

 other conditions being maintained as equivalent as possible. He 

 concluded, also, that the Ea. was derived almost entirely from fat, 

 by dividing the amount of dry solid disappearing from the egg by 

 the amount of chemical energy disappearing, thus finding that the 

 calorific value of the material disappearing was, on an average, 

 9000 cal. per gm. He then combusted some purified egg-fat and 

 obtained a calorific value of 9476 cal. per gm. Tangl did not fail 

 to point out how well this fitted in with the results of the chemical 

 analyses of Prevost & Morin; Liebermann, and Pott. 



Tangl next considered the relations between Ea. and the energy 

 stored up in the tissues of the embryo, though he did not discuss 

 this from the point of view of efficiency. Nevertheless, the table he 

 drew up is interesting, and is reproduced in Table 116. As develop- 

 ment goes on, the relation between storage and combustion changes, 

 for while at first the efficiency of storage is low, it rises as develop- 

 ment proceeds, and reaches 66 per cent, or so by the end of incubation. 

 This course of events has since been repeatedly confirmed. Tangl 

 expressed it by concentrating attention on the fact that the body of 

 the finished chick embry^o contains roughly 32 Gal. of chemical 

 energy, and the Ea. is roughly 16 Cal., therefore about | of the 

 original energy was used for storage, and | for combustion. The over- 

 all energetic efficiency was therefore 66 per cent. Tangl's figures for 

 calorific value of the embryonic tissues have already been discussed 

 in relation to the similar ones obtained by Murray — it is worth 

 noting, however, that Tangl did not find any notable alteration in 

 the calorific value of the unused yolk between the loth and 21st 



