REGULATION OF TEMPERATURE 249 



record of the temperature of the internal organs is ob- 

 tained from the rectum or from the urine. Normally 

 there is a daily fluctuation between 37-5° C. (99-5° F.) 

 in the evening and 36-2° C. (97-2° F.) in the early morning. 

 This is due to the greater bodily activity which occurs 

 during the daytime, for it is reversed in those who follow 

 nocturnal employment. 



The constancy of the temperature is due to a balance 

 between the heat produced and the heat lost. 



Heat is produced solely in the metabolic processes, 

 principally in the voluntary muscles. 



Heat is lost — 



(1) By radiation to the surrounding atmosphere; 



(2) By evaporation of sweat ; 



(3) By evaporation of water in the lungs ; 



(4) By discharge of warm excreta — carbonic acid, urine 



and faeces ; 



(5) By warming foods ingested cold. 



Heat regulation is seen in its simplest form in muscular 

 exercise when increase in heat-production is counter- 

 balanced by an increase in heat-loss brought about by 

 dilatation of the cutaneous blood-vessels and increased 

 evaporation of sweat from the skin and of water from the 

 lungs. 



Variations in the external temperature produce a two- 

 fold reaction — change in the amount of heat lost (physical 

 regulation) and change in the amount of heat produced 

 (chemical regulation). These alterations being in a re- 

 ciprocal direction the temperature remains constant. 



Physical Regulation 



The action of external cold upon the skin is to con- 

 strict the blood-vessels and to stop sweating. These 

 effects are produced reflexly through the central nervous 

 system, the sensory nerves constituting the afferent and 

 the sympathetic the efferent path. In the absence of 



