72 SECRETION. 



may be said to contain about \ per cent, of solids suspended and 

 dissolved in water. These solids are fats and fatty acids, sodium 

 chloride, epithelium, and a trace of urea. Besides these there is a 

 considerable amount of carbonic dioxide (C0 2 ) excreted by the 

 skin. 



What is the amount of sweat excreted in twenty-four hours ? 



About one and a half to two pints, but this varies greatly with 

 the environment. 



What factors affect the amount of the sweat ? 



The condition of the atmosphere, the nature and quantity of the 

 food, the amount of fluids consumed, the exercise taken, and the 

 relative activity of the other glands, especially of the kidneys. 

 Certain mental conditions, some diseases, and drugs also interfere 

 with sweat-secretion.* 



What ingredients produce the characteristic odor of perspiration ? 



The fatty acids formic, acetic, butyric, propionic, caproic, and 

 caprylic have been found. The odor of sweat varies in different 

 portions of the body. 



Upon what nervous mechanism does the production of perspira- 

 tion depend? 



It is probable that the sweat-glands are under the reflex control 

 of centres in the medulla and in the spinal cord, and that these 

 centres regulate this function of the skin through the vaso-motor 

 system. 



Is sweat-excretion necessary to life? 



Yes, because of the disturbance of heat-regulation by absence of 

 evaporation, or. perhaps, by absorption or retention of poisonous 

 matter. The symptoms are those of an acute poisoning pyrexia 

 and exhaustion. 



What is the character of the sebaceous glands ? 



The sebaceous glands occur everywhere over the entire skin sur- 



* Under conditions which exaggerate the flow of the perspiration, as hard 

 work in hot air, with free consumption of fluids, the amount of the perspi- 

 ration is said to exceed twenty pints in a day. 



