62 
On Malaria. 
be generated in abundance by vegetable fragments long dead and detached from 
the plant, by mere mud impregnated with unassignable vegetable matter, and also 
by such chemical substances as contain some of the elements of plants, without be- 
longing to them ; of which sugar, as I shall presently notice, oifers a conspicuous 
in To ascertain these facts is important, because they form the groundwork for 
precautionary measures as to disease, as will speedily appear ; while 1 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 iu 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 expended and dead portions ; or 
wherever fragments of plants are exposed to moisture; or wherever mud. impregnat- 
ed with invisible or dissolved vegetable matter, exists; or, finally, wherever any 
chemical compound of the vegetable elements is wetted or held in solution in water, 
there the poison iu question may he, or null be produced, provided the temperature 
he sufficiently high: and it is "this necessity for a certain temperature, which is 
the cause wliv that peculiar decomposition of vegetables which forms peat, does not 
produce malaria, however it may occur in peaty lands ; because, generally speaking, 
the formation of peat is limited to climates or regions of a low temperature. The 
nature and cause of the exception now made, will he explained immediately. 
I need not attempt to inquire further into the nature of this decomposition, 
since there are no facts on which to found an inquiry. What we must conclude, 
is, that some of the vegetable elements are let loose and re-combined into a new 
gaseous compound, while experiments carefully conducted (as ought not to be 
doubted when Vauquelin has been engaged in them) have not detected even the pre- 
sence of such a new substance ill the atmosphere of marshes, far less its nature. 
It is, however, evident that it cannot be any of the hydrocarburetted or other 
chemical gases which it has, at different times, been supposed ; while, remaining 
thus in darkness, the only test of its presence continues to be the effects as to 
disease which it produces on the human body. 
But, as I remarked, we possess enough knowledge of its natural history to assist 
us in guarding ourselves against its effects ; and as that question, utility, is the 
object of the present paper, I will proceed to describe as much of that as is admis- 
sible in so limited a space. To know all the classes or kinds of places which are 
capable of producing malaria, is the first and main object as to prevention : to 
know by what means it is propagated is the next, while the contingent circum- 
stances necessary to its production, or co its effects on the body, consisting chiefly 
in temperature and moisture under various modes, will also demand attention. 
All these things being known, we have laid the preliminary knowledge, requisite 
to prevention, as far as that is in our power; without them, we are subject to 
those hazards which arise from ignorance ; and what those hazards and their effects 
are, cannot be very obscure. when it is computed, and, perhaps, truly, that half the 
entire mortality of the world is the consequence of malaria: of the fevers chiefly 
which are its produce. 
But one circumstance requires to he premised; and this is, to prove that our 
own country can produce malaria, and is subject to its diseases ; because, were 
this not the fact, the statements of this paper could posstss but verv little interest 
to general readers, whatever it might to physicians or philosophers. I think I shall 
prove that we are all interested in them, and that also, to a considerable degree. 
The chief disorders produced by malaria are intermittent fevers, and what are 
called by physicians, remittent fevers: writing to general readers, we should call them 
fevers simply : while further, it is usual among the people, for them to receive the 
term typhus ; a name implying, strictly, contagious fever, and, as thus misapplied, 
a source, not of confusion merely, but of considerable evil in various ways. Not to 
enter into medical discussions, which would here lie inadmissible, I must be content 
with simply saying what is easily proved ; that the fevers, generally, which appear 
in summer, or from June to November, are of this class, and the produce of ma- 
laria ; while, that agues, as they are popularly called, are produced by the same 
cause, is admitted on all hands, 1 
Now, every one knows that such fevers do occur in summer, in many parts of 
England, and iu certain districts, very conspicuously ; and further, that while 
