EFFECTS OF EXTREME HEAT. 879 



to 72, each having, by simultaneous evaporation into the hot air, maintained 

 a comparative coolness. As the experiment proceeded, the temperature of 

 both rose to about 100, at which point the frog's temperature remained sta- 

 tionary, while that of the fungi, no longer able to undergo further evaporation, 

 continued to rise. The continuous exhalation from the moist skin of the frog 

 was the only cause which could explain the non-occurence of a further else in 

 its temperature. (De la Roche and Berger. ) 



The effect of evaporation, in reducing the temperature of the living 

 body, may also be illustrated by the results of experiments made on 

 sponges wetted, and porous vessels filled with hot water, and placed in 

 a dry oven, in which the air was still hotter ; these bodies actually 

 lose heat at first, evidently owing to temporary evaporation. 



It has been supposed that the living animal body may possess special 

 means of resistance to external heat, but of this there is no proof what- 

 ever. It may be entirely explained by the effects of evaporation. 



Thus, when the surrounding air is warm or hot, especially if it be 

 dry, the evaporation from the skin is increased, and so the tempera- 

 ture of the body is lowered ; whereas, in colder air, especially if this 

 be also moist, the diminished amount of evaporation tends so far to 

 conserve the animal heat. The increased perspiration excited by the 

 great heat of the skin furnishes, for a certain time, sufficient material 

 for evaporation. There is a limit, however, to the amount of this ex- 

 cretion, and also to its rapidity of evaporation ; for when the surround- 

 ing air becomes moist, a check being put to the evaporation, the body 

 is no longer thus defended, and its temperature begins to rise. Thus, 

 in a room, the temperature of which was 260, and the air dry, it was 

 found possible to remain for 8 minutes, by which time, the body was 

 not much elevated in temperature, although the clothes, and other 

 articles in the room, became very hot. (Blagden and Banks.) A case 

 is on record of a person remaining 10 minutes in a dry hot air-bath at 

 284 ; whilst Chabert, the so-called fire-king, went into ovens heated 

 from 400 to 600 ; but of course, for a much shorter period. Many 

 workmen employed in foundries or glass works also withstand very 

 high temperatures, the skin being profusely bathed with perspiration ; 

 these men of necessity drink large quantities of fluid. When, however, 

 the air is moist as well as hot, the temperature that can be endured is 

 much less ; for, in a vapor bath, at a temperature of only 120, the 

 body rapidly gains heat, as much as 70 in 10 minutes, and a feeling 

 of great and insupportable discomfort is experienced. (Berger and 

 De la Roche.) It is said, however, that, from habit, the Finns can 

 withstand, for upwards of half-an-hour, moist air or vapor baths grad- 

 ually raised to 158, or even 167. Animals surrounded by air 

 heated gradually to 200, speedily die, their temperature being then 

 raised about 13 above their natural standard. (The same authorities.) 

 This seems, accordingly, to be the extreme limit of heat endurable by 

 a warm-blooded animal. Most cold-blooded animals are killed by a 

 temperature of about 75. 



In civil life, even in temperate climates, direct exposure to the rays 

 of the sun is often fatal, producing some profound disturbance of the 

 nervous centres, caused either by congestion of the vessels of the brain, 



