THE HEAT OF THE BODY. 483 



nerve fibres exciting the sweat-centres from which the 

 secretory nerves for the sudoriparous glands arise and, partly, 

 directly on those centres, as they are thrown into activity, at 

 least in health, as soon as the temperature of the blood flow- 

 ing through the spinal cord is raised. In fever of course we 

 may have a high temperature with a dry non-sweating skin. 

 The more there is sweat poured out, the more heat is used 

 up in evaporating it and the more the Body is cooled. 



5. Our sensations induce us to add to or diminish the 

 heat in the Body according to circumstances; as by cold or 

 warm baths, and iced or hot drinks. 



As regards temperature-regulation by modifying the rate 

 of heart production in the Body, the following points may be 

 noted ; on the whole, such regulation is far less important 

 than that brought about by changes in the rate of loss, since 

 the necessary vital work of the Body always necessitates the 

 continuance of oxidative processes which liberate a tolerably 

 large quantity of heat. The Body cannot therefore be cooled 

 by diminishing such oxidations; nor, on the other hand, can 

 it be safely warmed by largely increasing them. Still, within 

 certain limits, the heat production may be controlled in 

 several ways : 



1. Cold increases hunger; and increased ingestion of 

 food increases bodily oxidation, as shown by the greater 

 amount of carbon dioxide excreted in the hours succeeding 

 a meal. This increase is probably due to the activity into 

 which the digestive organs and such metabolic organs as the 

 liver are thrown; hepatic-vein blood is about one degree cen- 

 tigrade (nearly two degrees Fahrenheit) warmer than portal- 

 vein blood, and during digestion much more blood flows 

 through the liver. 



2. Cold inclines us to voluntary exercise; warmth to 

 muscular idleness; and the more the muscles are worked the 

 more heat is produced in the Body. 



3. Cold tends to produce involuntary muscular move- 

 ments, and so increased heat production; as chattering of 

 the teeth and shivering. 



4. Cold applied to the skin increases the bodily chemical 

 metamorphoses and heat production. At least the tem- 

 perature in the armpit rises at first on entering a cold bath, 

 though the heat carried off from the surface soon over- 

 balances its increased production. The phenomenon may, 



