CONTROL OF BODY TEMPERATURE AND FEVER 743 



under the tongue for a minute or more, it is practically the same as the 

 temperature of the arterial blood of the hand when this is exposed to the 

 ordinary conditions of .outside temperature. Greater differences than 

 1 C. in the temperature of different regions of the body are often ob- 

 served in feeble individuals and in those with some circulatory disturb- 

 ance. 



FACTORS IN MAINTAINING THE BODY TEMPERATURE 



The body temperature represents the balance between heat production 

 and heat loss. The production is effected mainly in the muscles by the 

 oxidative processes which are constantly ensuing there. When the 

 activity of the muscles is abolished by paralyzing the terminations of 

 the motor nerves with curare, the temperature of warm-blooded animals 

 immediately falls or rises according to the temperature of the environ- 

 ment. A curarized warm-blooded animal is thus made to behave like a 

 cold-blooded one. Increased muscular activity, on the other hand, 

 promptly raises the body temperature by 1 or 2 C., above which, how- 

 ever, a further rise does not occur, provided nothing has been done to 

 interfere with the mechanism by which the excess of heat is got rid of 

 from the body. The temperature in such cases adjusts itself at a higher 

 level, at which it remains fairly constant however strenuous the exer- 

 cise. It is possible that a certain amount of heat may also be generated 

 by the chemical processes occurring in the liver and other viscera, but 

 when compared with the muscles this source of heat is undoubtedly in- 

 significant. Many of these chemical processes, as in the liver, instead 

 of producing, actually absorb heat, so that the balance between heat- 

 producing and heat-evolving mechanisms may or may not come out in 

 favor of the liberation of heat. 



The production of heat goes on all the time in muscles on account of 

 the condition of tonic contraction in which they are held (see page 905), 

 and which is also necessary for keeping the joints in the proper degree 

 of flexion or extension. When more heat is required by the animal body, 

 the tone of the muscles increases independently of the function which 

 they may be performing in controlling the position of the joints. This 

 increased tone may become so pronounced that it causes visible contrac- 

 tions, which we recognize as shivering. Whenever the insensible hyper- 

 tonicity and the shivering are inadequate to produce a sufficient amount 

 of heat, the animal instinctively moves about in order that the greater 

 contractions may liberate more heat. 



The heat is produced in the muscles by oxidation of the foodstuffs that 

 have been assimilated from the blood. Even during the process of as- 

 similation itself a certain amount of heat is generated; this is known 



