PT. Ill, SECT. 7] ENERGETICS AND ENERGY-SOURCES 947 



This was rightly regarded by Murray as outside the Hmits of the 

 standard errors. He concluded that either or both of the two 

 constants used in the calculations were too high for the protein and 

 fat of the embryo during the early stages of incubation, for, after 

 all, these constants have been exclusively derived from experiments 

 on adult tissues. It may, therefore, be assumed as probable that 



6.2 



6.0 





5.8 



6.5 



5.2 



5.0 



Days5 7 9 11 13 15 17 19 21 



IncQbation age 



© Murray, x Tangl. 

 Fig. 256. 



the true calorific constants for the substances present in early em- 

 bryonic life (in the case of the chick) should be regarded as lower than 

 those for the corresponding adult substances. It follows, then, that, 

 just as the fuel value per gram of organic matter rises with age, 

 so also the fuel value of either or both the protein and fat fractions 

 rises, due to the increasing proportion within each group of substances 

 with a relatively high calorific value. 



The opening up of the study of energy-relations in embryogenesis 

 is due to Tangl and his collaborators, who in a long series of papers 

 from 1903 onwards published the results of their extensive researches 

 with the bomb calorimeter. Eichwald's review presents some of their 



