THE SKIN, ITS APPENDAGES AND ITS FUNCTION. 43 



ing the terminations of the secretory nerves, while 

 pilocarpin produces an opposite effect in a similar way. 



On account of these sweat glands the skin becomes 

 next in importance after the kidneys in the excretion 

 of waste products. The quantity of sweat excreted 

 varies greatly and is hard to measure. It is influ- 

 enced by the temperature and humidity of the sur- 

 rounding air, by the nature and quantity of food and 

 drink consumed, by the amount of exercise, the rela- 

 tive activity of other organs, especially the kidneys, 

 and by certain mental conditions. The hotter it is, 

 the greater the amount of perspiration. In damp 

 weather there may be less perspiration, but it does not 

 evaporate and is therefore more in evidence. 



Ordinarily man has a temperature of 98.6. The 

 source of this body heat or temperature is the general 

 body metabolism, muscular activity, and activity of 

 the glands, especially of the liver, which is constantly 

 active, the blood in the hepatic vein being warmer than 

 that in any other part of the body. The tissue of the 

 brain also is said to be warmer than the surrounding 

 blood, and the heart and respiratory muscles, which 

 are in constant activity, are responsible for much of 

 the body heat. The amount of heat generated in the 

 body, therefore, varies at different times, according as 

 a person is awake or asleep, quiet or active. 



Temperature Regulation. The temperature is reg- 

 ulated by variations in the production and loss of heat, 

 less being known of its production than of its loss. It 

 has been calculated that four-fifths of the energy of 

 the body is converted into heat, one-fifth into work. 

 As the minimum amount of heat produced in twenty- 

 four hours is sufficient to raise 10 gallons of water from 

 to boiling-point, it is evident that if there were not 

 some way for the escape of much of this heat the body 

 would become hotter and hotter and finally destroy itself. 

 The temperature, however, except on the surface, is 

 uniform, heat being lost as fast as it is produced. For, 



