316 ANIMAL HEAT. 



a supply of food sufficiently ample to provide for the material demands 

 of the animal system. 



Resistance of the Living Body to High External Temperature. It 

 has been seen that, in the human subject and the warm-blooded animals 

 generally, an actual rise in the bodily temperature of 6 or 7 is certainly 

 fatal ; and yet the body may be exposed, as shown by repeated observa- 

 tions, to much higher degrees of heat without any injurious result. 

 According to Dr. Carpenter, the temperature of the air, in many parts 

 of the tropical zone, often rises, during a large portion of the year, to 

 43.3, and in some regions of India is occasionally above 50; while it 

 is well known that the air of manufactory dr3 r ing-rooms and of the 

 Turkish bath may be easily endured at a heat of considerably more than 

 45. Either of these temperatures would be fatal to man, if they indi- 

 cated the actual warmth of the internal organs. The body therefore 

 must either possess some means of diminishing its own production of 

 heat, or else of neutralizing, to a certain extent, temperatures which are 

 higher than that of the normal standard. 



The most direct and simplest means of moderating the temperature 

 of the body is that by the cutaneous perspiration. This fluid, derived 

 from the perspiratory glands of the skin, is a clear, colorless, watery 

 secretion, with a distinctly acid reaction, and a specific gravity of 1003 

 or 1004. Its constitution is as follows : 



COMPOSITION OF THE CUTANEOUS PERSPIRATION. 



Water 



Sodium chloride 



Potassium chloride ........ 



Sodium and potassium sulphates ..... 



Salts of organic acids 



1000.00 



It is accordingly a fluid of very simple composition, containing more 

 than 99^ per cent, of water, and more than half its solid ingredients 

 consisting of the inorganic alkaline chlorides. There are also present 

 in the perspiration traces of an organic substance similar to albumen, 

 and a free volatile acid, which gives to the fluid its acid reaction and 

 odor. 



The perspiration is a constant secretion. In a condition of repose or 

 of moderate bodily activity, it is exuded in so gradual a manner that it 

 is at once carried off by evaporation, and has received the name, under 

 these circumstances, of the insensible transpiration. The entire quantity 

 of fluid discharged in this way, according to the observations of Lavoi- 

 sier and Seguin, amounts on the average to 900 grammes per day. In 

 addition to this, about 500 grammes are discharged from the lungs, 

 making 1400 grammes of daily exhalation from the whole body. The 

 vaporization of this quantity of water will consume 750 heat units; or 



