80 On Hybernation. 



It has been observed that animals which do not hyber- 

 nate possess a temperature considerably higher than the 

 medium they inhabit, while those that do, are but a few 

 degrees more elevated than their surrounding medium. 

 Sir John Hunter, in his experiment on the power of ani- 

 mals producing heat, had frequent occasion to place fish in 

 a reduced temperature, and uniformly found that when the 

 subject of his experiment was no longer able to generate 

 heat sufficient to resist the effects of cold, the part frozen 

 could not be completely recovered. In all his experi- 

 ments upon the freezing of animals, he was unable to re- 

 store the actions of life by thawing, from which the con- 

 clusion may be drawn that circulation once completely 

 stopped, can never be recovered. An earth-worm frozen 

 at the same time was completely cead when thawed.* 



The moulting of birds as weV. as their migration is a 

 species of hybernation The first is a preparation for 

 winter, and their change of colour, adapting itself to the 

 season, frequeitly perplexes the ornithologist, and causes 

 spurious speci . 



The change of seasons produces its influence on the 

 secretive organs to increase the clothing of animals, as 

 well as the revers^^ ; Ihus we find the dogs of Guinea and 

 the sheep of Africa almost without fur, and in Scotland the 

 wool is pulled from the sheep when ready to fall off. 

 The same cause, perhaps, produces its effects more pow- 

 erfully on animal than on birds. The ermine, whose 

 fur is so valuable, undergoes lour changes. 



" During the summer months its hair is of a pale reddish 

 brown colour; in harvest it becomes clouded with pale 

 yellow; and in the month of November, with us, it is of 

 a snow white colour. Its winter dress furnishes the valu- 

 able fur called Ermine. Early in spring, it becomes 

 freckled with brown, and in the month of May it complete- 

 ly resumes its summer garb." — Edin. Encyc. Vol. X. part 

 2nd, D. 731. 



The migration of birds has been noticed by our earliest 

 historians, and their wonderful precision and order have 

 ever been a source of delight to the observation of the 

 student of nature. Their periods and habitation so well 



''= Animal Eaonomy, pp. 109, 112. 



