BODY HEAT 65 



is a true reflex. When the skin is exposed to cold the 

 cutaneous vessels are reflexly contracted, and radiation 

 is lessened. When exposed to heat the vessels are 

 dilated, and sweat secretion begins. Thus both radia- 

 tion and evaporation are rendered more active. It is 

 important for adequate and instantaneous temperature 

 regulation that the nervous apparatus concerned should 

 be kept in good working order, and part of the good 

 effect of a morning cold bath is no doubt to be attributed 

 to its putting the vasomotor nerves 'through their 

 drill.' It should be noted in this connection that the 

 cutaneous nerves are not tuned to appreciate actual 

 degrees of temperature, but merely a gain or loss of heat 

 from the skin. This explains why it is, for instance, 

 that when we go down into a ' tube ' railway in winter it 

 feels warm, but in the summer it feels cool, although the 

 temperature of the tunnel is really almost constant all 

 the year round. Mere sensation, therefore, is a most 

 fallacious guide to temperature, for which reason we 

 cannot trust to the hand in gauging the presence or 

 absence of fever in a patient, but have to fall back upon 

 the reading recorded by a thermometer. 



The chemical regulation of temperature by increasing 

 heat production is also a function of the nervous system. 

 It used not to be believed that this was so. It was 

 thought that cold stimulated the activity of the cells 

 directly. That, of course, was an error. Cold is really 

 a depressant of vitality, and paralyzes the cells just as a 

 narcotic does. The clinical effects of cold, indeed, if it 

 be sufficiently severe actually to lower the temperature 

 of the blood, are wonderfully like those of an anaesthetic 



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