On Malaria. 307 



are evolved during vegetable decomposition, e. g. the carbonic acid, 

 the carburetted hydrogen gases, carbonic oxide, he. has not yet put 

 us in possession of that form of matter of whose real existence we can- 

 not entertain a doubt, but which is more subtle than the rarest of 

 the gases ; an attenuated poison, which has not yet been imprisoned 

 and separately exhibited in our chemical vessels ; causa latet — vis 

 est notissima. But when we consider what has been done in pneu- 

 matic chemistry, in the last half century, we need not despair that 

 even the winged poison of malaria may be yet detected, indentified, 

 isolated, and even neutralized. If there be a vapor as subtle and 

 poisonous as that of prussic acid, created or evolved by vegetable 

 decay, nothing more would be necessary to produce all the effects 

 that are now so painfully notorious. The fact that trees and fresh 

 vegetables render atmospheric air salubrious by restoring the ne- 

 cessary supply of oxygen, when it is exhausted by animal respira- 

 tion, proves that in a living or growing state they do not contribute to 

 such a result : but decomposing vegetable materials, to a greater or 

 less amount, being found in every spot, from which this poison is 

 known to proceed, the inference seems to be almost inevitable, that 

 they supply the unknown pestilential agent, during the jorocess of de- 

 composition. 



It does not appear that one class of vegetables more than another 

 gives out the malarious poison, but it will be seen hereafter, that rank 

 herbage, such as juicy weeds, and subaquatic plants, decay more 

 rapidly, give off more moisture, and yield more effluvia in the same- 

 time and space, than those of more ligneous fibre. 



That this noxious material is innocent by itself, or perhaps not 

 separable without the aid of water, from its original combination with 

 vegetable matter, is also obvious ; for in a dry state, the constituent 

 parts of every species of vegetation are harmless ; and the vapor 

 given off in hay making, when no decomposing process is going on, 

 is not only innocent, but salubrious. 



It is presumed that animal matter furnishes no constituent part of 

 malaria, for although insects, and other animal remains, are daily per- 

 ishing in those places where these pestiferous exhalations arise, 

 sufficient to modify, and perhaps to characterize them, yet it is believ- 

 ed that animal decomposition does not produce fever ; because, the 

 manufacturers who use various animal substances when in their most 

 offensive state, are not subject to fevers, nor has any endemic fever 



