48 THE SKIN A REGtILAtOR OF ANIMAL KEAt. 



ried off by contact with a cooler air, the exhalation 

 from the skin is reduced to a very moderate amount 

 and that, in warm climates, where the heat is not 

 carried off in this way, the surface is constantly be- 

 dewed with perspiration, and a corresponding- appe- 

 tite exists for liquids by which the perspiration may 

 be kept up to a sufficient degree. Every one must 

 have experienced the grateful effects of this pro 

 vision, in passing from the dry, restless, and burn 

 ing heat, like that of fever, to the soft and pleasant 

 coolness which follows the breaking out of the 

 sweat. 



Attention to the order of events affords the requi* 

 site knowledge of the means employed for carrying 

 off the increased heat which is produced, when a 

 person is exposed to a warm air and powerful sun, 

 or engaged in severe exercise. At first the body is 

 actually felt to be warmer, the skin becomes dry and 

 hot, and the unpleasant sensation of heat is soon at 

 its maximum. By-and-by, a slight moisture is per- 

 ceived on the surface, followed by an immediate in- 

 crease of comfort. In a short time afterward, this 

 moisture passes into free and copious perspiration ; 

 and if the heat or exertion be still kept up, the sweat 

 becomes profuse, and drops from the body, or wets 

 the clothes which envelop it. A decrease of ani- 

 mal heat unavoidably accompanies this, because, 

 independently of any vital action contributing to 

 this effect, as is most probable, the mere physical 

 evaporation of so much fluid is itself sufficient to 

 carry off a large quantity of caloric. The curious 

 experiments of Edwards tend to show that evapora- 

 tion is really the only means required for reducing 

 animal heat to its proper degree ; but the results 

 obtained by him require to be confirmed, and^ the 

 experiments varied and carried farther, before* the 

 inquiry can be considered as completed. The saga- 

 city of Franklin led him to the first discovery of the 

 use of perspiration in reducing the heat of the body, 



