SOME SPECULATIONS OF HUNTER. 841 



state and well nourished, many of them lose it still 

 more rapidly in a very cold atmosphere, owing 

 to the large extent of radiating surface, compared 

 with the diminutive size of their bodies. So true 

 is this of young poultry, that they never thrive 

 and grow well at temperatures below 65, but pine 

 away gradually, and die of the roup, or some in- 

 fluenzal disease. It is therefore probable, that 

 the process of artificial incubation, and the rearing 

 of poultry, cannot be carried on so well in the 

 middle latitudes as in warm climates, like that of 

 Egypt, where nearly 100,000,000 are thus pro- 

 duced annually. 



It was maintained by John Hunter, that animal 

 temperature is an effect of the vital principle, ivhich 

 he supposed had the power of generating both heat 

 and cold. In support of his opinion that animal 

 heat is generated by the materia vitce, he observes 

 that when a dormouse was exposed to the influ- 

 ence of a freezing mixture, " it defied the cold 

 while the vigour of life lasted, but that when all 

 signs of life were extinguished, it became frozen." 

 (Phil. Trans, of the Royal Society, vol. Ixvi.) 

 But he might have said, that so long as a portion 

 of its heat remained, it retained a certain amount 

 of vitality ; and that when deprived of heat, it be- 

 came frozen or dead. He further maintains that 

 temperature is the effect of vitality, because a 

 longer time is required to congeal birds and mam- 

 malia, than reptiles and fishes, whose vitality is 



