21S EFFECTS OF HEAT ON THE ANIMAL ECONOMY. 



The faculty less 5. I think I hare shewn, that the faculty possessed by 

 extensive than man au< j an i ma i s f preserving a constant temperature, 

 though exposed to great heat, is much less extensive than 

 has generally been supposed from the experiments made by 

 er than that of Drs. Fordyce and Blagden ; and that it is by no means com- 

 lesisting cold, p^^e to the f acu i t y they have of resisting cold, and pre- 

 serving a temperature superior to that of the surrounding 

 medium. 

 What is its 6. Though this faculty is limited, it is nevertheless real : 



cause? jf. was an interesting inquiry therefore, to determine its 



cause. Does it reside wholly in the perspiration produced 

 by evaporation, as some physiologists suppose? The ex, 

 periments I have made render this opinion extremely proba- 

 ble, at least with respect to cold-blooded animals : but they 

 have not enabled me to decide, whether it be the same in 

 -animals with warm blood. I have only found, that inani- 

 mate substances, the surfaces of which were entirely wet 

 and susceptible of evaporation, acquired a less elevated tern, 

 jperature, when exposed to a high heat, than warm-blooded 

 animals under similar circumstances. 

 Xessoxigen 7. I afterward endeavoured to ascertain the influence of 



respiration at a heat on * ne phenomena of respiration. Dr. Crawford, who 

 high tempera- investigated this subject very minutely, imagined he observ- 

 ed, that the vitiation of the air by breathing was propor- 

 tionally less, as the heat to which the animal was exposed 

 was greater. In a considerable number of experiments I 

 made, I was not able to discover any constant proportion 

 between the vitiation of the air in which animals were in- 

 cluded and the temperature to which they were exposed. 

 JRodies dis*ect- $" Lastly I turned my attention to the circumstances, 

 «<J. that accompany death occasioned by exposure to heat ; and 



I particularly examined the state of the bodies of animals 

 thus killed. The phenomena that appeared on dissection 

 iowever, among which the most remarkable was a great 

 Muscular irri- diminution of muscular irritability, were not sufficiently 

 lLainithsS constant, to allow me to draw any conclusion respecting 

 the cause of this death. 



Observation* 



