The Skin and the Kidneys 



193 



Now, it is a law of physics that the change from liquid 

 to vapor involves a loss of heat. For instance, a few drops 

 of ether or of any volatile liquid placed fifl&^HI 

 on the skin produce a marked sense of 

 coldness, because the heat necessary 

 to change the liquid into vapor has been 

 drawn rapidly from the skin. This 

 principle holds good for every drop of 

 sweat that reaches the mouth of a sweat 

 gland. As the sweat evaporates, it 

 absorbs a certain amount of heat and 

 cools the body to that extent. 



\292. How the Action of the Skin may 

 be modified. After profuse sweating we 

 feel chilly from the evaporation of a 

 large amount of moisture, which rapidly 

 cools the surface. When the weather 

 is very warm the evaporation tends to 

 prevent the bodily temperature from 

 rising. On the other hand, if the 

 weather be cold, much less sweat is 

 produced, the loss of heat from the 

 body is greatly lessened, and its tem- 



, r c ,,. /r^ (Treated with osmic acid : 



perature prevented from falling. Thus showing three outer 



it is plain why certain drugs and hot 



baths are often given and other efforts 



are made to sweat the fever patient. 



The increased activity of the skin helps 



to reduce the bodily heat. 



> 293. The Secretion of Sweat and its 



Nervous Control. The sweat glands 



are under the control of certain nerve 



fibers originating in the spinal cord and 



FIG. 103. Transverse 

 Section through the 

 Human Skin. 



layers of the cuticle, two 

 in black and a middle 

 light layer. Below the 

 inner dark layer, the 

 active layer, or rete mu- 

 cosztm, is well shown. 

 All below is the true 

 skin. The tortuous 

 course of a sweat gland 

 is well marked. The 

 two round black spots 

 are fat cells. Magnified 

 30 diameters.) 



