On Malaria. 311 



by the unquestionable, and no less wide and severe experience 

 of France and Italy. 



To proceed with similarly unsuspected places, I may name all 

 kinds of ditches and drains, as these are constructed for agricul- 

 tural or other objects. These are, in their very essence, marshes, 

 and often of the worst quality ; since often in a state of putre- 

 faction which is more rare in a real marsh of any extent. And 

 very often they are the real cause of the fevers which continue 

 in a country after those operations by which it has been drained ; 

 Bs would easily be proved by a corresponding examination. 

 To know this fact, is, as in all other cases, to know the remedy, 

 as far as that is in our power; avoidance as the one generally 

 most easy, and further attention to keeping them clean and 

 free from weeds, — an attention not less required for agricultural 

 reasons. And that such is their power in exciting disease is 

 proved, not merely by the experience of modern France and 

 Italy, but by the remarkable fact that, in the times of ancient 

 Rome, perfectly informed at all times on this subject, such 

 regulations formed a part of the laws, both as to these recep- 

 tacles, and as to all canals. I need scarcely say that, in such 

 cases, a clean earthen bank is the easy remedy ; as, in the 

 case of ornamental waters, a stone margin is an effectual se- 

 curity — as far, at least, as the margins are concerned — since it 

 is equally necessary to avoid the growth of sub-aquatic plants 

 and the exposure of mud to the sun. 



I have thug described as minutely as I dare within these 

 narrow limits, the chief places or forms of land and water 

 which, as producing a living vegetation, are the sources of 

 malaria; reserving what relates to remedial processes, to a 

 future paper on this subject ; and I may now point out what 

 remains, consisting in vegetable decomposition independently 

 of vegetation. 



Among these, the sewers of towns are assuredly to be 

 reckoned : and as I can take a proof from France without the 

 hazard of offence, it is sufficient to mention, that the Salpe- 

 triere was formerly subject to intermittent fevers, which at- 

 tacked the inmates within the house ; and that these being 

 suspected to arise from the drains, these were closed up, with 

 the immediate consequence of exterminating the disease. It 



