TEMPERATURE REGULATION IN HOMOIOTHERMS 65 



the brain, altliongli the ordinary respiratory movements 

 are not disturbed. 



It would seem, therefore, that, although there may 

 be some grounds for believing that the nervous control 

 of heat regulation is widely distributed, the evidence 

 points to the conclusion that the temperature regulation 

 of the mammals is chiefly coordinated at the base of the 

 brain in the corpus striatum. 



The Temperature Sense. — The sensations of heat and 

 cold which an animal experiences from time to time are 

 caused by changes in the temperature of the skin. In- 

 numerable nerve endings are distributed over the skin 

 and these, when stimulated, evoke sensations of heat 

 or cold. Each responds to but one type of stimulus, i.e., 

 a warm object applied to a heat nerve ending elicits a 

 sensation of warmth. It has little or no effect upon a 

 cold spot. The reverse is also true. The sensitivity of 

 the human skin to temperature changes is very acute. 



It is an interesting correlation that the main channel 

 of heat elimination is through the skin, that the skin is 

 the only part of the body directly exposed to the environ- 

 ment, and that the sldn has widely distributed through 

 its outer layer the temperature sense organs. The skin 

 is the first part of an animaPs body to respond to tem- 

 perature variation in the environment. The physiologic 

 stimulus to the thermic end-organs is the passage of heat 

 through the skin from the interior to the surrounding 

 medium. Impulses are sent to the heat center. Thus the 

 heat center anticipates changes in actual blood tempera- 

 ture by compensatory reactions to changes in the skin 

 temperature. Consequently if radiation and conduction 

 are continuous and uniform, the end organs adapt them- 

 selves to the temperature of the surrounding medium. 



