HEAT LOST FROM THE SURFACE OF THE BODY. 465 



higher, there will be an actual gain. When the humidity of the air is great, 

 there will be reduced evaporation of perspiration and consequent diminished 

 heat loss. If we assume a moisture-saturated air at the body temperature, 

 then heat loss becomes impossible and the temperature of the body will 

 rise. This is why a hot moist climate is so oppressive, while a hot but dry 

 atmosphere is readily borne by the human body. The amount of heat 

 required to evaporate i c.c. of water is 536 small calories, hence an increase 

 in the evaporation of perspiration readily compensates for a decrease in the 

 loss of heat by radiation and convection. 



Many examples may be given of the power which the body possesses of 

 resisting the effects of a high temperature, in virtue of evaporation from the skin. 

 Blagden and others supported a temperature varying between 92 to 100 C. 

 (i98-2 i2F.) in dry air for several minutes; and in a subsequent experiment 

 he remained eight minutes in a temperature of 126.5 C- (260 F.). "The 

 workmen of Sir F. Chantrey were accustomed to enter a furnace, in which his 

 molds were dried, while the floor was red-hot, and a thermometer in the 

 air stood at 177 . 8 C. (3 50 F.), and Chabert, the fire king, was in the habit of 

 entering an oven the temperature of which was from 205-3i5 C. (400- 

 600 F.)." (Carpenter.) 



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

 to prevent evaporation from the body. C. James states that in the vapor 

 baths of Nero he was almost suffocated in a temperature of 44.5 C. (112 F.), 

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

 moded by a temperature of 80 C. (176 F.). In the former, evaporation from 

 the skin was impossible ; in the latter it was abundant, and the layer of vapor 

 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. 



Man is able by suitable clothing to increase or to diminish the amount of 

 heat lost by the skin. There are baths and other means which man and 

 animals instinctively adopt for lowering the temperature when necessary. 



Although under any ordinary circumstances the external application of 

 cold only temporarily depresses the normal temperature to a slight extent, it 

 is otherwise in cases of high temperature in fever. In these cases a cool 

 bath may reduce the temperature several degrees, and the effect so pro- 

 duced lasts in some cases for many hours. 



Extreme heat and cold produce effects too powerful, either in raising or 

 lowering the heat of the body, to be controlled by the proper regulating ap- 

 paratus. Walther found that rabbits and dogs kept exposed to a hot sun, 

 reached a temperature of 46 C. (114.8 F.), and then died. Cases of sun- 

 stroke furnish us with several examples in the case of man; for it would seem 

 that here death ensues chiefly or solely from elevation of the temperature. 



The effect of mere loss of bodily temperature in man is less well known 

 than the effect of heat. From experiments by Walther it appears that rab- 

 bits can be cooled down to 8 . 9 C. (48 F.) before they die, if artificial respira- 

 tion be kept up. Cooled down to 17.8 C. (64 F.), they cannot recover 

 30 



