SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 775 



time that the squabs were ready to leave the nest. They distinguished 

 four factors in the installation of this function, (i) the change in 

 the surface/volume ratio, (2) the development of feathers, (3) the 

 development of an internal dissipating surface (the air-sacs) prob- 

 ably under nervous respiratory control, and (4) heat-production 

 in metaboHsm. Of these they regarded the third as perhaps the 

 most important. 



In a later paper Pembrey found that mice and rats at birth have 

 not attained the capacity for heat regulation. When they are naked, 

 blind, and unable to run about, they cannot maintain a constant 

 temperature, and cannot regulate the production of heat at low 

 temperatures. When they are about 8 days old, they have a protecting 

 coat of fur, and though still bhnd are much more active — at this 

 stage they give some evidence of having acquired the power. At 

 10 days old they are as homoio thermic as the adults, Gulick's later 

 statement that mice and rats are fully homoiothermic at birth 

 cannot be accepted on the basis of his insufficient evidence. Exactly 

 similar results were obtained on pigeon squabs, as has already been 

 mentioned, so that the pigeon and the hen among oviparous animals 

 correspond respectively to the rabbit and the guinea-pig among vivi- 

 parous ones. More recently, Ginglinger & Kayser have confirmed 

 the work of Pembrey and have linked up, as we have already seen, 

 the genesis of heat-regulation with the peak in metabolic rate. Their 

 results may be summarised as follows : 



Form of heat-regulation present at birth 



Chemical Physical 



Guinea-pig . . 



Chick 



Rabbit 



Man 



Cat 



Mouse 



Pigeon 



It may not be irrelevant here to mention, in connection with 

 body-temperature, that the so-called "broody fever", i.e. a tempera- 

 ture higher than normal for sitting hens, has been shown by Simpson 

 to be without factual basis. 



