498 ON INCREASE IN SIZE [pt« iii 



use. Rubner's book contains a discussion of this matter, from which 

 it is to be concluded that, at present, there is no rule which covers 

 all the cases. [See also Hollis and Szabo.] 



Rubner's "second law", in which he laid down that the total 

 amount of heat eliminated from birth to death in all the higher 

 mammals is the same, i.e. about 191,600 Calories per kilo, with 

 the exception of man, for which the value was 725,700 Calories 

 per kilo, has often been criticised adversely, and does not here con- 

 cern us. But it is to be observed that it contradicts the lack of relation 

 found by Moulton and others between simple gestation time and 

 life-span, in that, according to Rubner, a constant percentage of the 

 total heat eliminated during life has been eliminated at birth, i.e. 

 2500 out of 191,600 or 1-305 per cent. This proportion does not, of 

 course, hold in the case of man, but will be greater because of his 

 prolonged stay in utero. 



Our immediate aim must now be to examine the effects of various 

 physical influences upon the rate of growth of the living embryo, 

 for by the aid of such a study one may hope to penetrate further into 

 the fundamental nature of the process. That chemical influences can 

 also exert a great effect on the growth of the embryo is obvious, but 

 they will be dealt with in succeeding chapters, such as the sections 

 on vitamines, and general metabolism. At present the discussion will 

 be strictly confined to the effects of radiant energy (heat and light) 

 on the rate of growth, and all teratological considerations will be 

 kept in the background. 



2' 14. The Effect of Heat on Embryonic Growth 



The accelerating influence of rise of temperature on embryonic 

 growth was known to William Harvey, though in an unformulated 

 kind of way, for referring to differences in gestation time, or what he 

 calls "the diversity of going with Child", he says: "For the same 

 thing befalls them as happeneth to Plants, whose fruits and seeds, 

 do more slowly and seldom arrive to maturity in cold Countries, 

 than do other Plants of the same kind which are in a fat and warme 

 soile. So Orenges in England adhere to the trees almost two whole 

 years together, before they come to maturity: and Figgs also scarce 

 ever arrive at any perfection here, which are ripe in Italy twice or 

 thrice a year. And the like befalleth the fruits of the Womb". But 

 perhaps the earliest quantitative observation of the effect of heat on 



