258 



HITCHCOCK'S ANATOMY 



phere, and we are constantly giving off heat to the air which 

 envelops us. 



453. Manner in which the Body is maintained at its 

 uniform Temperature. — The manner in which the body is 

 kept at the uniform temperature of 98°, is a subject of deep 

 interest. It is partly accomplished by radiation, since the 

 body is ordinarily warmer than the air about it, and also 

 partly by inhaling the cool air into the air passages. It is a 

 well-known principle in chemistry, that, when any substance 

 passes from a more solid to a less solid condition, as from 

 solid to liquid, or liquid to a gas, heat is absorbed, or, in more 

 common lan^uao'e, cold is made sensible. This is seen in the 

 application of water, alcohol, or ether, to the skin, when a 

 sensation of cold is felt, which is owing to the fact that the 

 substance applied is passing from the form of a liquid to 

 that of a vapor. Now the same thing takes place when the 

 perspiration is allowed to evaporate from the surface of the 

 body. The increased flow of blood, as brought about by the 

 exercise, or the high temperature of the surrounding at- 

 mosphere, stimulates the vessels of the skin to more energetic 

 action, and sensible perspiration is poured out upon the sur- 

 face of the body. This, however, is now in contact with the 

 currents of air always present about the body, and it is readily 

 thrown out into a state of vapor, and in accordance with the 

 chemical principle just state I, heat is absorbed from the body 

 producing its uniform temperature. 



458a. It should be mentioned here, that of late many 

 experiments have been carried on which seem to show us 

 that the above-mentioned theory of animal heat can not be 

 fully adopted. For it is well known that many chemical 

 combinations besides those of mere oxydation or " burning" 

 produce heat; and many of these processes are constantly 

 taking place in the body. But all the facts hitherto ad- 



458. How is the body kept at its uniform temperature? What chemical principle 

 illustrates this view ? 458a. Give the result of recent experiments. 



