COOLING OF ANIMALS EXPOSED TO GREAT HEAT. 373 



a question which, as may be seen from the facts I hare 

 adduced, is not essentially connected with that here dis- 

 cussed. 



In frogs, and I believe it would be the same with other Remark on 

 cold-blooded animals, the difference between their tempe-'^^^ss- 

 rature and that of the surrounding me<^ium was always 

 much less striking than in warm-blooded animals, as might 

 naturally be expected. This however has afforded me an Curious fact re- 

 opportunity of making a remark somewhat curious, but^P^*^*^'"? ^hem. 

 requiring to be confirmed by repeated experiments, namely, 

 that the proper heat of these animals, or the excess of their 

 temperature over that of the surrounding medium, is as 

 considerable when they are exposed to heat, as when they 

 are exposed to cold. This would seem to indicate, that the 

 cause of this heat is not the same as in warm-blooded ani- 

 mals. 



From what has been said we may conclude, that the pro- The production 



duction of cold, manifested in animals exposed to a high °^*;°'^ '" ^"i- 



r o mals owing to 



degree of heat, is to be classed with those phenomena, the evaporation, 

 essential cause of which is physical. In this however we 

 cannot overlook the inEijence of vital causes, which, as I in which -vital 

 have announced at the commencement of this paper, concur*^^"^^^ concur, 

 Avith the physical causes in the production of almost all the 

 phenomena, that are the result of organization. In fact, 

 the evaporation, that causes this production of cold, can- 

 not take plaee, unless the surface of the body and of the 

 pulmonary cells be kept constantly moist. And here the 

 comparison of inorganic bodies, such as were employed in 

 my experiments, ceases to be exact. The surfaces of the^c 

 ■were moistened by transudation only. Those of animals 

 are moistened by perspiration, a very complex phenomenon, 

 necessarily depend on the action of the system of capillary 

 vessels. In the former, the surface no soorier begins to 

 dry, than it draws from the interior a new portion of mois- 

 ture. In the latter, on the contrary, perspiration must 

 acquire a fresh degree of activity, when the hedt becomes 

 more considerable; and this can take place only from an in- 

 creased energy in the exhalant system, and perhaps evea 

 throughout the whole of the circulation. It is to be ot)-. ; 



served, that this increased activity of the perspiration, at 

 1., least 



