SECT. 2] 



AND WEIGHT 



407 



smaller finished fish. These results are curious, for it is generally- 

 understood that temperature changes alter the rate at which a 

 growth-process goes on yet not the amount of end-product formed. 

 The work of Barthelemy & Bonnet on the frog is an exact parallel 

 to that of Gray on the trout, for these workers raised frog embryos 

 at different temperatures with the following results : 



(P.E.G.) 



(P.E.C.) 



If the second and third columns of this table are compared it will 

 be seen that in the first series the French workers did get results like 

 those of Gray, i.e. the higher the temperature the greater the com- 

 bustions and the less the storage, but that in the second series there 

 was no such effect to be observed. The Plastic Efficiency Coefficient 

 (P.E.C.) is the most convenient way of expressing this relation (see 

 Section 6- 1 o) . According to Gray it should change with temperature, 

 for assuming his trout embryos to have the same percentage composi- 

 tion, no matter what the temperature, those raised at 15° would con- 

 tain (each) 21*3 mgm. solid and consequently (since the eggs contain 

 43-4 mgm. solid) would have a P.E.G. of 0-50, while those raised 

 at 10° would contain (each) 24-2 mgm. solid and consequently would 

 have a P.E.C. of 0*56. I shall return to this subject in the section 

 on general metabolism of the embryo; here it is only necessary to 

 remark that the subject is clearly not yet settled and requires much 

 more attention than it has so far received. At the same time, 

 returning to the main theme, it must be remembered that Gray only 

 made use of these temperature phenomena as one of the supports for 

 his theory. 



He drew another support from the fact that if his equations were 

 correct, the product obtained by multiplying the dry weight of yolk 

 by the dry weight of embryo should be at a maximum on the 71st 

 day of development. This he found to be actually the case, as is 



