46 THE INTEGUMENT, OR SKIN, 



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 perspira- 

 tion. Under the influence of heat or exercise, however, 

 this fluid is excreted more abundantly, and appears on the 

 surface in the form of 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 this excretion, in the adult, 

 is not far from thirty ounces, nearly two pints, or more 

 than nine grains each minute. 



17. The Uses of the Perspiration. Besides liber- 

 ating from the blood this large amount of water, with the 

 effete matter it contains, the perspiration serves to regulate 

 the temperature of the body. That is to say, as evapora- 

 tion 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 this vapor of the body, the heat of 

 the atmosphere apparently increases, and the discomfort 

 therefrom is relatively greater. 



18. The importance of this excretion is shown by the 

 effects that often follow its temporary interruption, namely, 

 headache, fever, and the other symptoms that accompany 



1 5. 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 

 perspiration perform ? Explain the process. 



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



