772 DURATION OF LIFE IN 



the negroes of all ages does not exceed twenty- 

 three years;* arid that the annual number of 

 births is not equal to the number of deaths. 



Such facts exhibit in a very striking manner 

 the fatal influence of tropical climates on Euro- 

 peans, compared with the negro race. But why 

 is the mortality of the whites so much greater in 

 central Africa than in the East and West Indies? 

 And why so much greater in all hot countries 

 than among the natives? The rationale of the 

 latter problem has been already given, when 

 treating of the manner in which the develope- 

 ment of the chest, and the quantity of respira- 

 tion are modified by external temperature, and 

 will be further explained hereafter. The truth 

 is, it is much easier to counteract the influence 

 of external cold, by suitable clothing, habitations, 

 artificial combustion, and a liberal supply of 

 animal or oily food, than it is to avoid the de- 

 bilitating tendency of a burning climate, and the 

 noxious exhalations which it inevitably engen- 

 ders, wherever there is vegetable and animal 

 matter in a state of decay. 



The greater mortality of tropical Africa than 

 of the West Indies, must also besought in^the 



* It is therefore not true, as maintained by Dr. Prichard and 

 others, that the mean duration of life is about the same in all 

 climates. Solomon tells us that fourscore was an extreme age in 

 Judea. But we have seen that in Europe and the United States, 

 it is frequently twenty, and sometimes fifty or sixty years longer. 

 And Dr. Smith, who resided some time in Peru, informs us, that 

 at Lima, the mean duration of life does not exceed twenty years. 



