306 On Malaria. 



in a greater degree. I have already said that putrefaction is 

 not necessary ; while the fact that the most pernicious situa- 

 tions in the world are the banks of the tropical rivers, and the 

 lands perpetually washed by a clear green sea, shows con- 

 vincingly the little truth of this popular judgment. The rivers 

 which I have just named, and many more among us, includ- 

 ing the Thames in many places, are decidedly productive of 

 disease, though running streams ; but the evidences are too 

 notorious everywhere to need urging. And therefore, when, 

 with regard to mill-dams or other ponds, forming the class of 

 waters next to be noticed, it is popularly said that ^hey cannot 

 be pernicious, because the water is constantly refreshed by a 

 stream, it is a false as well as a dangerous opinion. Should 

 such a receptacle admit a stream that replaced the whole water 

 in a few hours, which is rarely the case, it would, even then, 

 be no other than a slow river, and therefore no more free of 

 danger than the worst of those. 



In proportion as any species of soil or place is least sus- 

 pected, and most common, it seems the more necessary to be 

 careful in pointing it out and dwelling on it ; and hence it is, 

 that I am more desirous of urging the dangers arising from 

 what will, I know, be despised, as I have experienced it to be. 

 I allude here to a great variety of apparently insignificant 

 waters, comprising mill-ponds, for various purposes, and on 

 all scales ; ornamental waters and fish-ponds, canals, and the 

 endless pools and ponds found all over the country, in deserted 

 gravel pits, and in various other casual situations not worth 

 detailing. 



It is always useful to examine any case of this nature by re- 

 ducing it to its principles, or by a philosophical analysis, and 

 to inquire whether it ought not to be insalubrious, before in^ 

 quiring whether it actually is so. Now all these waters, be 

 they what they may, include the elements of a marsh or of a 

 water productive of malaria. Their margins are marshes, they 

 contain aquatic and putrefying plants ; and under the heat of 

 summer, they disclose mud impregnated with vegetable matter. 

 And this is true of the whole, whatever their extent or charac- 

 ter may be : while, if plainly shown that bulk or space is not 

 necessary even to a marsh, and that our climate is adequate to 



