TEMPERATURE-REGULATION IN THE BODY. 455 



-quickened respirations, too, increase the evaporation of water 

 from the lungs and, thus, the loss of heat. 



3. Warmth directly dilates the skin-vessels and cold con- 

 tracts them. In a warm room the vessels on the surface 

 dilate as shown by its redness, while in a cold atmosphere 

 they contract and the skin becomes pale. But the more 

 blood that flows through the skin the greater will be the 

 heat lost from the surface and vice versa. 



4. Heat induces sweating and cold checks it ; the heat 

 appears to act, partly, reflexly in exciting the sweat-centres 

 from which the secretory nerves for the sudoriparous glands 

 arise, and, partly, directly on those centres, which are thrown 

 into activity, at least in health, as soon as the temperature of 

 the blood is raised. In fever of course we may have a high 

 temperature with a dry non-sweating skin. The more sweat 

 there is 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 heat 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 tol- 

 erably 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 con- 

 trolled 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 are thrown. 



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. 



