PERSPIRATION. 353 



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 Hair. The hairs serve an important purpose in the protec- 

 tion 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 

 quantity of hair upon the general surface is small, as it is a very imperfect 

 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 running 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, which is very important in per- 

 sons exposed to dust in long journeys or in their daily work ; and 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 situations, but 

 their general uses are sufficiently evident. 



PERSPIRATION. 



In the fullest acceptation of the term, perspiration embraces the entire 

 action of the skin as an excreting organ and includes the exhalation of carbon 

 dioxide as well as of watery vapor and organic matters. The office of the 

 skin as an eliminator is undoubtedly very important ; but the quantity of 

 excrementitious matters with the properties of which physiologists are well 

 acquainted, such as carbon dioxide and urea, thrown off from the general 

 surface, is small as compared with what is exhaled by the lungs and discharged 

 by the kidneys. If the surface of the body be covered with an impermeable 

 coating, death occurs in a very short time ; but the phenomena which precede 

 the fatal result are difficult to explain. All that can be said upon this point 

 is that death takes place when the heat of the body has been reduced to about 

 70 Fahr. (21 C.), and that suppression of the action of the skin in this way 

 is always followed by a depression of the animal temperature. Warm-blooded 

 animals die usually when more than one-half of the general surface has been 

 varnished. Rabbits die when one-fourth of the surface has 'been covered 

 with an impermeable coating (Laschkewitsch). Valentin and Laschkewitsch 

 found that when the temperature was kept at about the normal standard by 

 artificial means, no morbid symptoms were developed. The cause of death 

 in these experiments has never been satisfactorily explained ; and it is not 

 easy to understand why coating the surface should be followed by such a 

 rapid diminution in the general temperature. The experimental facts, how- 

 ever, indicate that the skin probably possesses important uses with which 

 physiologists are unacquainted. Urea and some other effete products have 

 been detected in the perspiration, but it is probable that some volatile mat- 

 ters are eliminated by the general surface, which have thus far escaped ob- 

 servation. 



Sudoriparous Glands. With few exceptions, every portion of the skin 

 is provided with sudoriparous glands. They are not found, however, in tne 



