62 THE INTEGUMENT, OR SKIN 



were all united, end to end, their combined measurement would 

 exceed three miles. 



15. The Sensible and Insensible Perspiration. The pores of 

 the skin are constantly exhaling a watery fluid; but, under 

 ordinary circumstances, there is no moisture apparent upon 

 the surface, for it evaporates as rapidly as it is formed. This 

 is called insensible perspiration. Under the influence of heat 

 or exercise, however, this fluid is formed more abundantly, 

 and appears on the surface in minute, colorless drops. It is 

 then termed 'sensible perspiration. 



16. Water is the chief component of this fluid, there being 

 about ninety-eight parts of water to two parts of solid matter. 

 The quantity escaping from the body varies greatly, according 

 to the temperature of the air, the occupation of the individual, 

 and other circumstances. The average daily amount of per- 

 spiration in the adult is not far from two pints, or more than 

 nine grains each minute. 



17. The Uses of the Perspiration. Besides liberating from 

 the blood this large amount of water, with the worn-out matter 

 it contains, the perspiration serves to regulate the temperature 

 of the body. That is to say, as evaporation always diminishes 

 temperature, so the perspiration, as it passes off in the form 

 of fine vapor, cools the surface. Accordingly, in hot weather 

 this function is much more active, and the cooling influence 

 increases in proportion. When the air is already charged with, 

 moisture, and does not readily receive the vapor of the body, 

 the heat of the atmosphere apparently increases, and the 

 discomfort therefrom is relatively greater. 



18. The importance of perspiration is shown by the effects 

 that often follow its temporary interruption, namely, headache, 

 fever, and the other symptoms that accompany "taking cold." 

 When the perspiration is completely checked, the consequences 



15. What is sensible perspiration ? Insensible perspiration ? 



16. Components of perspiration ? Upon what does perspiration depend ? Amount of 

 perspiration daily ? 



17. What, does perspiration set free from the blood ? What other service does perspira- 

 tion perform ? Explain the process. 



18. Effect of interruption of excretion ? What experiments are mentioned f 



