978 ENERGETICS AND ENERGY-SOURCES [pt. m 



constituent substances and their balance, nor do tlie yolk and white 

 remain chemically constant. Perhaps the embryo at the 5th day of 

 development has much more to do to whatever it is absorbing to 

 turn it into itself than has the embryo of the 15th day, and con- 

 sequently the wastage is greater. 



This seems at first sight to be in contradiction with the facts known 

 about the "white yolk" (see p. 286) which, as Spohn & Riddle's 

 work showed, resembles the embryonic tissue much more than it does 

 the yellow yolk. But it is reasonable to suppose that this phase would 

 be passed through by the 5th day, at which time the A.E.E. curve 

 begins, and we might predict that when the efficiency of the earlier 

 stages is known, it will turn out to be higher, perhaps as much as 60 

 per cent. The A.E.E. curve would then become trough-shaped, like 

 the P.E.C. curve (see Fig. 254). 



The argument due to Terroine would thus be that in the earlier 

 stages the raw materials are more unlike the embryonic body in 

 composition than they are later. An interesting calculation which 

 shows that this is to some extent true is shown in Table 125, where 

 first of all the absolute amounts of the three main cell-constituents, 

 carbohydrate, protein and fat, are set down, both for the embryo 

 and for the raw materials, i.e. for the remainder of the egg. Then 

 these figures are expressed as percentages of the sum of the three in 

 each case and given in Cols. 8 to 13, so that we have side by side 

 the variations in balance of the three classes of substance throughout 

 development. 



Difference between the two figures {embryo and remainder) in Table 125. 



At the beginning At the end 



(4th day) (20th day) 



Carbohydrate (Cols. 8, 1 1 ) ... ... 2-3 0-3 



Protein (Cols. 9, 12) ... ... ... 29-5 9-5 



Fat (Cols. 10, 13) 31-8 9-8 



It can hardly be a coincidence that all three should work out Hke 

 this, but too much emphasis must not be laid on the calculation in 

 view of the fact that the sets of figures used for it are derived from 

 the results of several workers using not very homogeneous material. 

 A more serious shortcoming of such a calculation is that it assumes 

 that the embryo must be absorbing throughout an aHquot part of the 

 raw materials, although we may be reasonably certain that this never 

 happens at all. And again the efficiency curve involves quahtative 



