114 ANIMAL HEAT. 



ascertained. All birds have their animal tem- 

 perature at a high ratio ; and in the Trochilido', 

 so remarkable for the comparative size of the 

 heart, for the strength and rapidity of respira- 

 tion, for the extraordinary power of the muscles 

 of locomotion, their incessant labour, their capa- 

 bility of constant exercise during successive 

 hours without fatigue, and for the nervous en- 

 ergy of the system, we cannot doubt but that 

 animal temperature is at a maximum. If this 

 be so, it is not unreasonable to imagine that it 

 will enable these birds to endure a degree of 

 cold against which, from their tiny delicate 

 frame, they would seem incapable of struggling. 

 That this is the case with some of the most 

 sylphlike of these beings, the dainty Ariels of 

 their race, has been already shewn. At the 

 same time, the power of the vital forces in coun- 

 teracting the influence of cold differs, we con- 

 jecture, in various species, and also according to 

 an abundant or scanty supply of food, in the 

 same species. We cannot agree with those who 

 imagine that the soft, thick, downy nests which 

 these birds generally construct are thus designed 

 to furnish as much warmth as possible, on the 

 supposition that the body of the parent being 

 so small, the quantity of animal heat given off 

 must be in proportion. The Humming-bird, in 

 her deep soft nest, covers only two eggs, and 

 that to these her body affords sufficient warmth 

 we may conclude from Captain Lyon's account, 



