524 PHYSIOLOGY. 



ncea and thermotaxis. When heat is thrown on the body the polyp- 

 nceic center telegraphs the respiratory center to work more rapidly 

 to throw off more moisture by the expired air. 



The" afferent nerves of the thermotaxic apparatus are probably 

 those nerves in the skin administering to the "hot" and "cold" spots. 



Regulation of Loss of Heat, or Thermolysis. Heat is lost by an 

 animal in various ways. It may be by direct radiation and conduc- 

 tion from the skin, by the extraction of heat during the process of 

 evaporating perspiration, by warming the respired air, and by the 

 discharge of urine and fasces. 



SKIN KADIATION AND CONDUCTION. The skin is the main means 

 of escape of the bodily heat. Nearly three-fourths of the heat which 

 escapes from the economy does so through the skin as a means. 



A marked difference between the temperature of the skin and 

 that of the surrounding atmosphere constitutes a prime factor in 

 radiation. When the enveloping medium is very cold radiation from 

 the skin's surface is very rapid. 



The cutaneous circulation has considerable to do with the dissi- 

 pation of heat. The caliber of the peripheral vessels is governed by 

 the vasomotor system, which is itself under the guidance of the cen- 

 tral nervous system. 



External heat reflexly causes dilatation of the cutaneous vessels, 

 so that at such times the skin becomes red and engorged. It con- 

 tains more fluids and thus is a better conductor of heat. More blood 

 being at the body surface allows of greater and more rapid loss 

 through radiation. 



External cold reflexly causes a contraction of the peripheral ves- 

 sels; so that their lumina are narrowed. In consequence there is 

 less blood circulating in the skin, which appears pale and contains 

 less fluid; so that the radiation of heat is markedly hindered. 



By reason of nervous stimulation the sweat-glands are at times 

 made to functionate very freely; whereupon the skin's surface be- 

 comes bathed in a sensible perspiration. For the conversion of this 

 moisture into vapor heat is necessary. It is by the abstraction of 

 this heat from the underlying tissues that the body owes much of 

 its loss when its parts are hyperpyrexial. One pound of water in 

 evaporating takes up 1047 B. H. U. daily. 



The covering of the body by clothing during various seasons of 

 the year contributes much to the proper regulation of loss of heat, 

 so that the mean temperature may be maintained fairly constant. 



FEVER, The process of fever is one of, absorbing interest dur- 



