On Malaria. 307 
are evolved during vegetable decomposition, e. g. the carbonic acid, 
the carburetted hydrogen gases, carbonic oxide, &c. 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 motorious. The fact that trees and fresh, 
vegetables render atmospheric air salubrious by restoring the ne- 
ae 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 PEOCEAS: -of de- 
composition. 
Tt does not appear shot one class Vv egetables more: ethan ceases 
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 semen 
time and space, than those of more ligneous fibre. 
That this noxious material is innocent by itself, or oanear on 
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 ons 
is not only innocent, but salubrious. 
- It is presumed that animal matter furnishes no constituent part of | 
malaria, for although inseets, 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 a nor has any endemic fever 
