26 CLASS REPTILIA. 



without interrupting the course of life, and the circulation 

 of the fluids. This is witnessed in frogs, salamanders, and 

 marine tortoises, which dive under water, or bury themselves 

 in mud for entire days. The colder the atmosphere is, the 

 longer these animals can subsist under water, without having 

 occasion to respire the air, and without perishing, for they 

 are then in a state of semi-torpor. But in warm weather, 

 the respiration of the atmospheric air becomes necessary, and 

 the reptiles enjoy a more active life. 



In consequence of the imperfect respiration of reptiles, the 

 vital air combines with the portion of blood which is exposed 

 to it, in small quantity only, and disengages very little heat 

 from the sanguine fluid ; for the degree of heat is always in 

 proportion to the extent of the respiratory function. Accord- 

 ingly, these animals are all cold, and the temperature of their 

 blood exceeds, by a very few degrees, that of the atmosphere ; 

 while the birds, as we have formerly observed, which respire 

 so vigorously, are always exceedingly hot, and almost burn- 

 ing ; in fact, they are naturally, and habitually, in a state 

 which would be pronounced fever in a mammiferous animal. 



If the reptiles are naturally cold, the rigour of winter may 

 be presupposed to exercise a powerful influence over them. 

 This, accordingly, is the fact. They all grow torpid during 

 the cold season, and do not awaken until spring expands its 

 genial warmth. In this state of torpor they are immoveable 

 and almost frozen. Their blood circulates very slowly. 

 Their sensibility and life are suspended; they remain 

 plunged in a profound sleep, and lose scarcely any thing by 

 transpiration, because they are covered by a thick, coriaceous, 

 and almost impermeable skin. 



It is also in consequence of this natural coldness of rep- 

 tiles, that we must account for their almost total disappear- 

 ance from the polar regions, and the more rigorous latitudes 

 of the north, while on the contrary they are excessively mul- 



