PERSPIRATION 



315 



that there is no diminution in the pigment, but that the greater part of 

 the medulla becomes filled with air, small globules being also found in 

 the cortical substance. The hair in these cases presents a marked 

 contrast with hair that has gradually become gray from old age, when 

 there is always a loss of pigment in the cortex and medulla. How the 

 air finds its way into the hair in sudden blanching, it is difficult to 

 understand ; and the views that have been expressed on this subject by 

 different authors are entirely theoretical. 



The fact that the hair may become white or gray in the course of a 

 few hours renders it probable that many of the cases reported on unsci- 

 entific authority actually occurred ; and these have all been supposed 

 to be connected with intense grief or terror. The terror was very 

 marked in the case reported by Landois. In the great majority of 

 recorded observations, the sudden blanching of the hair has been appar- 

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

 protection of the general surface and in guarding certain of the orifices 

 of the body. The hair on the head and face protects from cold and 

 shields the head from the rays of the sun during exposure in hot cli- 

 mates. Although the quantity of hair on the general surface is small, as 

 it is an 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 persons exposed to dust in long 

 journeys or in their daily work ; and the short stiff hairs at the open- 

 ings 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 exhala- 

 tion of carbon dioxide as well as of watery vapor and organic matters. 

 The office of the skin as an eliminator is 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 is covered 



