936 GENERAL METABOLISM 



* Fiske & Boyden by independent reasoning, arrived at 0-96 for this value, and 

 Sznerovna's data give 0-92. 



Out of 100 gm. of protein in its diet, then, the embryo can store 

 away 98, out of 100 gm. of carbohydrate 82, but out of 100 gm. of fat 

 only 43. In the case of animals such as the trout, which burn large 

 amounts of protein, the "foodstuff P.E.C." will be very different. 



The average P.E.C. can be calculated for a number of other 

 organisms: 



The average efficiency of transfer of the material yolk and white 

 into the material of the embryo seems, then, to be constant for a 

 wide variety of species. But it is now generally recognised that these 

 average figures give very little information about what is actually 

 going on, and it is therefore necessary to enquire how the P.E.C. 

 varies during the developmental process. We ha\e no data for this 

 in the case of any other animal than the chick, except Gray's work 

 on the trout. The growth-rate of this embryo falls off during the 

 later stages of its development, and as its metabolic rate (respiratory 

 intensity, or maintenance intensity) was found by Gray to remain 

 constant, then evidently its efficiency must get smaller as it grows. 

 This relative constancy in the metabolic rate differentiates it sharply, 

 of course, from the chick (see Figs. 126 and 143). Gray accordingly 

 computed the P.E.C. for each successive half-gram of yolk, with the 

 following results: 



