REGULATION OF THE ANIMAL TEMPERATURE. 317 



about one-fifth of all the heat produced in the body during twenty-four 

 hours. 



The cutaneous secretion may be greatly increased by temporary causes. 

 An elevated temperature or unusual muscular exertion, will increase the 

 circulation through the skin and largely augment the amount of fluid 

 discharged. It then exudes more rapidly than it can be carried off by 

 evaporation, and collects upon the skin as a visible moisture, whence it 

 is known as the sensible perspiration. The amount of perspiration dis- 

 charged during violent exercise has been known to rise as high as 350 

 or 380 grammes per hour ; and Dr. Southwood Smith 1 found that the 

 laborers employed in heated gas-works sometimes lost, by both cutane- 

 ous and pulmonary exhalation, nearly 1600 grammes in the course of an 

 hour. The evaporation of this increased quantity of fluid consumes a 

 large portion of the caloric derived from the heated atmosphere, and 

 thus prevents an undue rise in the temperature of the bodily organs. 



It is possible that certain influences transmitted through the nerves 

 may also have the power of controlling directly the molecular activity 

 of the tissues, and may thus diminish the amount of internal heat at 

 the source of its production ; but the experimental evidence of this 

 action is yet incomplete, and its mode of operation comparatively 

 obscure. 



The production of heat in the animal body and the regulation of its 

 temperature, by which it is maintained at or near a normal standard, 

 are two of the most important phenomena presented by the living organ- 

 ism. They are the result of an associated series of vital actions, and 

 at the same time essential conditions for the continuance of life. 



1 Philosophy of Health. London, 1838, chap. xiii. 



