On Malaria. 47 



that the real cause lies in the malaria transported or conveyed 

 by those winds or fogs, and of which they are the true and 

 best repository and vehicle. 



And these are the reasons for thinking that the malaria, with 

 the wind, may be transported to a distance as great as that 

 which the present view requires ; most easily perhaps in a fog, 

 but without difficulty even in a clear wind. It is remarkable 

 that the east wind, as it is the most persevering, is that one 

 also which preserves the most steady horizontal and linear 

 course. J have also shown, in a former work, that it is a pro- 

 perty of winds to travel in distinct lines through a tranquil 

 atmosphere, and often in streams of a very limited breadth ; that 

 opposing streams will also move, in absolute contact ; and that 

 even rapid streams of wind will cross each other's courses with- 

 out difficulty. This proves that, in any such stream, there is 

 a principle of self-preservation or integrity, and renders it pro- 

 bable that the several portions retain the same relative places 

 to each other, at any distance, during the career of the whole : 

 and there is a proof of this afforded in the fact of those 

 columns or streams of insects which are brought over by such 

 winds, and very frequently from those very countries, or from 

 Holland and Flanders, in the most regular order, or without 

 disturbance or dispersion. 



Hence it may be argued, that if a malaria, generated any 

 where and conveyed by the winds, can be transported to a dis- 

 tance of three miles, as has been proved, there is no reason 

 why it should not travel much farther, or to any distance that 

 can be assumed : and if this be true of a clear wind, the case 

 of a fog is even a much stronger one; since there is little 

 reason to doubt that the individual parts of such fog, in any 

 assumed mass, will retain their relative places to each other, as 

 perfectly after a journey of any given number of miles, as they 

 did at the point of production ; and if a portion of malaria has 

 been united to a portion of fog, in the marsh which produced 

 both, or whence both have come, there is every apparent 

 reason why it should be found in that same portion at any 

 farther or assumed distance, because there is no cause for 

 either its dispersion or its decomposition. 

 • A fog is a cbud, simply ; and it is notorious that a single 



