BODILY TEMPERATURE. 21 



MAINTENANCE AND REGULATION OF BODILY TEMPERATURE. 

 The chemical changes which take place throughout the 

 system during the process of waste and repair, are accom- 

 panied by the production of heat, and consequently render the 

 temperature of the body higher as a rule, than that of the 

 surrounding air. On the other hand, radiation, evaporation 

 (principally from the lungs and skin), and conduction of 

 heat by contact with objects of lower temperature, reduce 

 this heat. The balance between these respective processes of 

 heating and cooling is not left to chance, but is maintained 

 within narrow limits by the nervous system. Although the 

 temperature of the surface of the body is subject to extensive 

 fluctuations, that of the interior cannot be kept higher than 

 say 104 F. or lower than 96 F. for even a few hours without 

 grave disturbance of health ensuing. The power of the 

 regulating action of the nervous system on the temperature of 

 the body is by no means absolute ; for we find that by pro- 

 longed exposure to great atmospheric heat in the tropics, the 

 nervous system may lose its power of control, and heat 

 apoplexy may ensue with a sudden and abnormally high rise 

 (say, over 107 F.) of temperature. As the rapidity of evapo- 

 ration, in circumstances of equal atmospheric temperature, 

 varies in inverse proportion to the quantity of moisture in the 

 air ; heat apoplexy occurs among horses as a rule, only in hot 

 damp climates, like that of Calcutta for instance. We should 

 here note that the evaporation of perspiration and not the mere 

 pouring out of that fluid on the skin by the sweat glands, is 

 an effective means for cooling the surface. The glare ol a 

 tropical sun seems to exert a very disturbing influence on the 

 heat-controlling power of the nervous system ; for we find that 

 a thick shade to the eyes (preferably made of a bad conductor 

 of heat, like pith or wood for example) affords great 

 protection from sunstroke to animals which work under the 



