REGULATION OF TEMPERATURE 251 



muscular tone. Heat-production, however, cannot be 

 diminished below the hasal metabolism which, we have 

 seen, amounts to about 2500 C. When this hmit is reached 

 the temperature can only be maintained at a constant 

 level by increased loss of heat — that is by radiation and 

 evaporation. 



Radiation is facilitated by the constant removal of the 

 warmed air from the surface of the body; it is therefore 

 more effective in a wind than in a still atmosphere. As 

 the surrounding temperature rises, conduction diminishes 

 and evaporation comes more and more into play, until 

 when the temperature of the air is as high as or higher 

 than that of the body evaporation becomes the sole avenue 

 for heat-loss. The effectiveness of evaporation depends 

 upon the degree of saturation of the air with water- vapour. 

 When the air is so hot that radiation cannot occur, and so 

 humid that evaporation cannot occur, the heat-regulating 

 mechanism breaks down and the body temperature rises. 



A centre for the regulation of temperature is said to 

 exist in the corpus striatum. Damage to this area leads to 

 rise of temperature. Stimulation with water colder than 

 the blood leads to shivering and vaso-constriction, stimu- 

 lation with, water warmer than blood to diminished muscular 

 tone and to vaso-dilatation. The rise of temperature which 

 occurs during fevers (pyrexia) is attributed to the stimu- 

 lation of the centre by the toxic products of the infective 

 process. 



