196 ANIMAL HEAT. 



been considered almost solely with regard to the ordinary case 

 of man living in a medium colder than his body, and therefore 

 losing heat in all the ways mentioned. The importance of the 

 means, however, adopted, so to speak, by the skin for regulat- 

 ing the temperature of the body, will depend on the conditions 

 by which it is surrounded ; an inverse proportion existing in 

 most cases between the loss by radiation and conduction on the 

 one hand, and by evaporation on the other. Indeed, the small 

 loss of heat by evaporation in cold climates may go far to com- 

 pensate for the greater loss by radiation ; as, on the other hand, 

 the great amount of fluid evaporated in hot air may remove 

 nearly as much heat as is commonly lost by both radiation and 

 evaporation in ordinary temperatures ; and thus, it is possible, 

 that the quantities of heat required for the maintenance of a 

 uniform proper temperature in various climates and seasons 

 are not so different as they, at first thought, seem. 



Many examples might be given of the power which the 

 body possesses of resisting the effects of a high temperature, 

 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. M. C. James states, that in the 

 vapor baths of Nero he was almost suffocated in a tempera- 

 ture of 112, while in the caves of Testaccio, in which the air 

 is dry, he was but little incommoded by a. temperature of 176. 

 In the former, evaporation from the skin was impossible ; in 

 the latter, it was, probably, abundant, and the layer of vapor 

 which would rise from all the surface of the body would, by 

 its very slow 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 lowering his tem- 

 perature 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 im- 

 portance. As a regulating power, the inferiority is still more 

 marked. The air which is expelled from the lungs leaves the 



