ANIMAL HEAT. 307 



new fluid, chyle, is formed out of the solids, which constitute 

 the food. By all these processes, animal heat must necessa- 

 rily be generated. 



12. But in order to the production of animal heat, by the 

 action of the capillary vessels, two conditions are necessary. 

 (One is, the presence of arterial blood ; the other, the action 

 of the nervous system) That arterial blood is necessary, is 

 shown by the operation of tying the vessels which supply a 

 limb with blood. } The consequence always is, that the tem- 

 perature immediately falls, and such limbs have to be wrap- 

 ped in cotton, and other means used to preserve a comforta- 

 ble degree of warmth. jThat nervous influence is also 

 productive of animal hea is shown by dividing, in like 

 manner, the nerves which go to any part.) The temperature 

 of a paralytic limb is always lower than that of the sound 

 one. 



13.( It may be concluded then, that respiration, circula- 

 tion, and nervous influence^ all co-operate in producing 

 animal heat, or that they are conditions essential to this 

 phenomenon. We here also perceive a circle of actions ; 

 or a chain, composed of many links, no one of which can 

 be spared. Each one contributes to a result essential to 

 organic existence, and one of the most curious and wonder- 

 ful which the mind can contemplate. 



14. If these principles be correct, we should expect to 

 find the greatest heat in those animals whose structure is 

 the most complex ; whose organic or vital actions are the 

 most intense ; and whose changes are the most rapid. Now 

 all these conditions belong to the warm-blooded animals es- 

 pecially, and particularly to (birds, j whose temperature 

 exceeds, by several degrees, thai of man. In them, as I 

 have already stated&respiration is more perfect, and the cir- 

 culation more rapid\ 



15. Upon the same principles, it would also follow, that 

 animal heat would be the higli3st in those portions of the 

 bodj/where the organic actions are most active^ And such 



