SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



741 



lation only) and with the guinea-pig (which can fully control its tem- 

 perature at birth). Correspondingly the guinea-pig — like the Berk- 

 shire pig — obeys the classical rule of descending heat-production from 

 birth onwards ; these animals have, as it were, settled on their thermal 

 neutrality point before birth and as it is kept steady we can observe 

 the effects of decreasing relative surface. The pigeon and the mouse, 

 on the other hand, are born without any regulatory power, and their 

 metabolic rate goes on increasing until this is attained. Intermediate 

 between these two groups come such animals as the rabbit, which can 



3 5 7 9 11 13 15 17 19 

 Mulblples of the initial weight 

 Fig. 166 ^. 



resist cold at birth but not heat, i.e. which have a partial regulatory 

 power. These show an increasing metabolic rate for a short time only, 

 and the curve for the rabbit in Ginglinger & Kayser's figure ( 1 66 b) 

 compares interestingly with that for man in the graph of Dubois ( 1 65) ^. 

 And the fact that the chick's metabolic rate is declining throughout 

 its incubation-period from the 5th day onwards would agree with the 

 finding that its heat-regulative power is fully developed at birth. The 

 peak of metabolic rate in mammals is explained by Ginglinger & 

 Kayser, then, as being due to their varying degrees of heat-regulative 

 power, but would this explain the peak on Gayda's curve for the toad, 

 which never succeeds in regulating its temperature at all ? 



1 And with those for growing calves given by Brody. 



