PERSPIRATION 199 



from being long overdiluted by too much water. If, 

 for any reason, water is drunk in such small quantities 

 that the blood has bat little to spare, the amount of water 

 excreted by the kidneys is correspondingly reduced. 



Importance of the kidneys. The importance of the 

 work of the kidneys is most clearly seen when through 

 disease their action is impeded or stopped. The conse- 

 quent accumulation of waste substances in the blood 

 results in headache, convulsions and even death. 



Excretion by the skin. The skin, as well as the 

 kidneys, removes a certain amount of waste products 

 in the form of perspiration. The perspiration when 

 analyzed is shown to contain a considerable amount of 

 various salts, especially sodium chloride, some fat and 

 minute traces of other substances which are also found 

 in the kidney excretion. Its bulk consists of water, 

 which under normal conditions is being constantly elimi- 

 nated in this way throughout life. When, through dis- 

 ease, the kidneys fail to do their work, the urinary sub- 

 stances are found in much greater amounts in the per- 

 spiration. Their excretion may be further increased by 

 inducing copious perspiration through hot air baths. 

 The failure of the kidneys may thus be partially neu- 

 tralized by the increased activity of the skin as an ex- 

 cretory organ. 



Uses of perspiration. Perspiration serves a threefold 

 purpose. It not only aids in removing the excess of 

 water from the blood, but it also keeps the skin both 

 moist and cool, even when the perspiration is so slight 

 in amount that it evaporates as quickly as it is secreted 

 and so is not perceptible or "visible." When perspira- 

 tion fails for -any reason, as in fever, the skin becomes 

 dry and harsh and the body is no longer properly 

 cooled. 



