PERSPIRATION. 131 



recorded observations, the sudden blanching of the hair has 

 been apparently connected with intense mental emotion ; 

 but this is all that can be said on the subject of causation, 

 and the mechanism of the change is not understood. 



Uses of the Hairs. The hairs serve an important pur- 

 pose in the protection of the general surface and in guarding 

 certain of the orifices of the body. The hair upon the head 

 and the face protects from cold and shields the head from the 

 rays of the sun during exposure in hot climates. Although 

 the amount of hair upon the general surface is small, as it is a 

 very bad conductor of caloric, it serves in a degree to maintain 

 the heat of the body. It also moderates the friction upon the 

 surface. The eyebrows prevent the perspiration from run- 

 ning from the forehead upon the lids ; the eyelashes protect 

 the surface of the conjunctiva from dust and other foreign 

 matters ; the mustache protects the lungs from dust, a func- 

 tion very important to those exposed to dust in long journeys 

 or in their daily work ; the short, stiff hairs at the openings 

 of the ears and nose protect these orifices. It is difficult 

 to assign any special office to the hairs in some other situ- 

 ations, but their general uses are sufficiently evident. 



Perspiration. 



In the fullest acceptation of the term, perspiration em- 

 braces the entire function of the skin as an excreting organ, 

 and includes the exhalation of carbonic acid as well as of 

 watery vapor and organic matter. The office of the skin as 

 an eliminator is undoubtedly very important ; but the quan- 

 tity of excrementitious matters with the properties of which 

 we are well acquainted, such as carbonic acid and urea, thrown 

 off from the general surface, is small as compared to the 

 amount exhaled by the lungs and kidneys. If the surface 

 of the body be covered with an impermeable coating, death 

 always takes place ; but the phenomena which precede the 

 fatal result are difficult to explain. The experiments on this 



