AND PREVENTION OP MALARIA. 223 



humanity. Macculloch says : " I trust to prove in this 

 essay, that the causes of malaria exist under numerous 

 circumstances not at all suspected in our country, and in 

 thousands, tens of thousands of places, even at our very 

 doors" (p. II, ed, 1827). Again: "Malaria produces in 

 itself a far wider mass of human misery than any other 

 cause of disease ; as, for the world at large, it is also the 

 cause of far more than half the mortality of mankind" 



(P- 31)- 

 In the examination of different districts for organic 



matter in the air, I have invariably found that low grounds 

 well cultivated have shown more than high grounds or 

 hills, and more than the open sea. I cannot, therefore, 

 doubt that the remarks of Dr. Macculloch are correct as 

 to the very general occurrence of unwholesome influences 

 caused by the state of the ground. I am inclined to go 

 further, and to say that even in places where we cannot 

 find that health is in any way injured, emanations arise. 

 But it is not sufficient that health should be injured, or at 

 least the average age reduced below the standard of the 

 country, in order that a place may be called insalubrious. 

 It may be that the impulse given to life may be dimi- 

 nished in some districts by substances rising from the 

 ground, whilst in other districts an entire or greater 

 freedom from all noxious exhalations may allow the supply 

 of the purest air, with all its highest quickening effects. 



The cause of malaria has been with great certainty 

 traced to the soil. I shall not revert in this place to the 

 arguments and observations which have led to this conclu- 

 sion. It is true that some places are exposed to emana- 

 tions of gases from subterranean reservoirs, but gases such 

 as can be prepared by the chemist, combinations of inor- 

 ganic bodies, are not known to be able to produce the 

 agues and peculiar fevers which we connect with the true 

 malarious district. Atmospheric phenomena, the condition 



