On Malaria: 295 



places ought to be suspected, Bud, in the view to prevention^ 

 avoided. 



That it is the produce of vegetable decomposition cannot, 

 apparently, be questioned, because, if it were extricated from 

 living plants, it should be found in thousands of situations 

 where it is unknown ; and that it belongs to wet soils, and also 

 to hot countries, or to a high temperature, further proves that it 

 depends on that process of decomposition which notedly occurs, 

 in these circumstances, most rapidly and extensively. But a 

 difficulty remains in attempting to determine what is the pecu- 

 har quality or stage of this decomposition under which it is 

 produced; whether it is the process commonly called putrefac- 

 tion, or some change among the elements of plants of a different 

 nature. 



One point is at least proved ; viz,., that it is not necessarily 

 accompanied by any smell, or that it is not an odorous substance 

 in itself. It may exist in abundance and virulence, without 

 being sensible in this manner ; and hence it had been thought 

 this arose from some mutual action of vegetables and water, 

 which was independent of proper decomposition. This, how- 

 ever, must be an incorrect opinion ; or the living vegetable is 

 not required for its production : since it is fully proved to be 

 generated in abundance by vegetable fragments long dead and 

 detached from the plant, by mere mud impregnated with un- 

 assignable vegetable matter, and also by such chemical sub- 

 stances as contain some of the elements of plants, without 

 belonging to them ; of which sugar, as I shall presently notice, 

 offers a conspicuous instance. 



To ascertain these facts is important, because they form 

 the groundwork for precautionary measures as to disease, as 

 will speedily appear ; while I may here make one remark as an 

 example of the utility of this knowledge : it is, that while there 

 is a popular fear with respect to putrid and stagnant waters, 

 there is none respecting clear waters, under whatever form, 

 producing living vegetables, and free of smell, while the danger, 

 in reality, may be scarcely less in the one case than in the 

 other. 



Generally, therefore, we must conclude, that wherever plants 

 in contact with water undergo decomposition, even as to their 



