SECT. 2] 



AND WEIGHT 



495 



potential energy stored in the tissues, but must to some extent be 

 wasted in upkeep metabolism, a wastage would be expected in the 

 case now under consideration, and as the relative surface of the new- 

 born is larger the smaller it is itself, this wastage would be expected 

 to be greater. Rubner then assumed that the heat production 

 of the embryo was about seven-tenths of the new-born animal, 

 presumably on the basis of premature birth figures, but also on 



Fig. 75- 



theoretical grounds drawn from the embryo's existence in a thermo- 

 static hydrosphere unaccompanied by much muscular or digestive 

 exertion. This assumption seems a dangerous simplification, in view 

 of the peak in basal metabolism which we now know to exist in 

 some animals before and in some animals after birth. However, 

 Rubner calculated the intra-uterine heat production as follows : 



Birth-weight of 

 animal (kilos) 



50-0 



25-0 



12-5 



625 



Cals. put out by 

 I kilo * per day 



23-9 

 298 

 42-0 

 46-6 



* I.e. seven- tenths of the post-natal figures. 



