REGULATION OF HEAT. 



2 4 I 



"body possesses of resisting the effects of a high tempera- 

 ture, in virtue of evaporation from the skin. 



Sir Charles Blagden and others supported a temperature 

 varying between 198 and 211 F. in dry air for several 

 minutes; and in a subsequent experiment he remained 

 eight minutes in a temperature of 260. But such heats 

 are not tolerable when the air is moist as well as hot, so 

 as to prevent evaporation from the body. Mr. C. James 

 states, that in the vapour baths of Nero he was almost 

 suffocated in a temperature of 1 12, while in the caves of 

 Testaccio, in which the air is dry, he was but little incom- 

 moded by a temperature of 176. In the former, evapo- 

 ration from the skin was impossible ; in the latter, it was, 

 probably, abundant, and the layer of vapour which would 

 rise from all the surface of the body would, by its very 

 slowly conducting power, defend it for a time from the full 

 action of the external heat. 



(The glandular apparatus, by which secretion of fluid 

 from the skin is effected, will be considered in the Section 

 on the Skin.) 



The ways by which the skin may be rendered more 

 efficient as a cooling- apparatus by exposure, by baths, and 

 by other means, which man instinctively adopts for lower- 

 ing his temperature when necessary, are too well known to 

 need more than to be mentioned. 



As a means for lowering the temperature, the lungs and 

 air-passages are very inferior to the skin ; although, by 

 giving heat to the air we breathe, they stand next to the 

 skin in importance. As a regulating power, the inferiority 

 is still more marked. The air which is expelled from 

 the lungs leaves the body at about the temperature of 

 the blood, and is always saturated with moisture. No 

 inverse proportion, therefore, exists between the loss of 

 heat by radiation and conduction on the one hand, and 

 by evaporation on the other. The colder the air, for 

 example, the greater will be the loss in all ways. Neither 



