39 



move the skin, and whose common use is 

 to shake off insects that annoy the animal, 

 are set in motion all over the body, and 

 this adds to the heat production, by in- 

 creasing the waste of tissue, — just as the 

 exercise of the muscles of locomotion have 

 that effect when the animal is at work. 



Now, if the air becomes warmer, or the 

 horse is exercised, the coat will slowly fall. 

 Thus, when it is necessary to keep in and 

 preserve the heat, the coat rises, and prac- 

 tically becomes thicker, just enough to pre- 

 serv^e the proper equilibrium of tempera- 

 ture, not allowing it to fall much below 

 99 degrees, and when it is necessary to 

 increase the heat dissipation, the coat falls, 

 or slowly becomes moist, just enough to 

 control the temperature from rising above 

 99 degrees. 



