176 PHYSIOLOGY FOR BKCJINNERS CHAP, xvi 



more heat is lost than in hot weather, but this is made up 

 for by a slight increase of production, so that the tempera- 

 ture of the body does not change. Cold slightly increases the 

 production of heat, while warmth slightly diminishes it ; so 

 that the body temperature is kept constant not only by regu- 

 lating the amount of loss, but also by regulating to a small 

 extent the amount of production of heat. This regulation is 

 carried out by the nervous system determining on the one hand 

 the loss by governing the supply of blood to the skin and the 

 action of the sweat glands, and on the other hand the produc- 

 tion by diminishing or increasing the oxidation of the tissues. 

 In a cold-blooded .animal this regulation does not occur, so that 

 the temperature of a frog or a snake falls in winter and rises in 

 summer. The cold of winter renders the cold-blooded animal 

 torpid, while the warmth of summer leads to active movements 

 and rapid oxidation. 



