.. COOLINe OF ANIMALS EXPOSED TO GREAT HEAT. SQ'J 



ed these results, I did not pretend to decide, that evapora- 

 tion was the true cause of the phenomenon in question ; I 

 merely held out this opinion as plausible : at present I think 

 I can give direct proofs of its justice. 



If evaporation be the sole cause that produces the re- Test <^ its rf^ 

 frigeration of animals exposed to a high degree of heat, it^'^^'^y 

 is evident, that by suppressing it both on the surface of the 

 body and in the interior of the lungs, this refrigeration will 

 be prevented, and the animals must acquire a temperature 

 equal or superior to that of the medium, in which they are 

 immersed. If we do not obtain this result, it is a proof of 

 the insufficiency of this cause : if, on the contrary, the 

 means employed for suppressing evaporation being such as 

 not to disturb the exercise of the other functions of the 

 animal, we perceive a cessation of the phenomenon, for 

 which we are endeavouring to account; we may conclude, 

 with equal reason, that it was owing to evaporation. 



This mode of ascertaining the influence of evaporation Experiments 

 an this phenomenon naturally offered itself to the minds of ^^'^ *^'^^^^''' 

 those, who have instituted inquiries on the subject. Some 

 experiments have been tried with this view ; but they have 

 neither been numerous, nor very decisive. One was by Dr. by Dr. Fordyce 

 Fordyce. This gentleman, having introduced a large quan- 

 tity of aqueous vapour into a heated room, thought he 

 perceived, that the heat incommoded him more, but that 

 his temperature remained scarcely the less stationary. It is 

 to be observed, that the time he passed in this room was 

 too short, to heat very perceptibly a mass so considerable 

 as that of the human body. No positive inference there- 

 fore can be drawn from this experiment ; any more than 

 from that, in which Dr. Crawford attempted to ascertain and Dr. Craw- 

 the influence of a warm bath on the temperature of a dog; ^^ ' 

 the mode in which he measured this temperature being too 

 inexact, and, besides, the effect of the water being capable 

 of suppressing the cuticular evaporation merely, not the 

 pulmonary. The experiments which the same gentleman 

 tried with frogs, animals in which the pulmonary evapora- 

 tion must be inconsiderable, would be more decisive, if the 

 results he gives were agreeable to observation. But I have 

 satisfied myself, that this is not the case. Numerous ex- Frogs acquire 



periraents, '^^ ^^"^^^"^^^ 



