44 WONDERS OF ORGANIC LIFE. 



is produced by evaporation. The effects of the 

 wine-cooler may be taken as a familiar illustra- 

 tion. The reason of this production of cold is 

 as follows : — During the conversion of liquid 

 (water, ether, alcohol, etc.) into vapour, caloric 

 is absorbed, and by this absorption cold is 

 generated, and the more so the more rapidly 

 the conversion is carried on, insomuch that 

 fluids may be frozen even during the heat of 

 summer. Hence it is that ether feels colder 

 than water from the rapidity with which it 

 evaporates. Now, in the experiment of Dr. 

 Fordyce above noticed, a rapid evaporation or 

 conversion of moisture into most attenuated 

 vapour, was taking place simultaneously from 

 the lungs and the whole surface of the skin. 

 The heat to which the body was exposed led to 

 the vast increase of the natural exhalation 

 which always takes place ; and, therefore, the 

 skin felt cold, and the breath caused the quick- 

 silver of the thermometer to sink. Dr. Fleming 

 denies that the body is kept cool by evapora- 

 tion, because, when Dr. Fordyce was conduct- 

 ing his experiments in heated air, water poured 

 down in streams over his whole surface ; and 

 he infers that this water was merely the vapour 

 of the room condensed by the coldness of his 

 skin, for at the same time a Florence flask, 

 filled with water of the same temperature with 

 his body (then 100°,) was bedewed with con- 

 densed vapour in a similar manner. Now this 

 does not prove that exhalation did not perform 

 a great part in the generation of cold, and we 



