and the Mode of its Communication. . 77 



If this supposition should turn out to be well founded, 

 the knowledge of the fact would enable us to explain 

 several interesting phenomena, and particularly that 

 most curious process by means of which living animals 

 preserve an equal temperature, notwithstanding the vast 

 quantities of heat that are continually generated in the 

 lungs, and notwithstanding the great variations which 

 take place in .the temperature of the air in which they 

 live. 



It is evident, that the greater the power is which an 

 animal possesses of throwing off heat from the surface 

 of his body,* independently of that which the surround- 

 ing air takes off, the less will his temperature be affected 

 by the occasional changes of temperature which take 

 place in the air, and the less will he be oppressed by 

 the intense heats of hot climates. 



It is well known that negroes and people of colour 

 support the heats of tropical climates much better than 

 white people. Is it not probable that their colour may 

 enable them to throw off calorific rays with great facil- 

 ity, and in great abundance ; and that it is to this cir- 

 cumstance they owe the advantage they possess over 

 white people in supporting heat ? And, even should it 

 be true, that bodies are cooled, not in consequence of 

 the rays they emit, but by the action of those frigorific 

 rays they receive from other colder bodies (which I 

 much suspect to be the case), yet, as it has been found 

 by experiment that those bodies which emit calorific 

 rays in the greatest abundance are also most affected by 

 the frigorific rays of colder bodies, it is evident that in 

 a very hot country, where the air and all other sur- 

 rounding bodies are but very little colder than the sur- 

 face of the skin, those who by their colour are prepared 



