On Malaria. 
69 
and the growth of aquatic vegetables converts them into so many petty marshes— 
often also exposing to the sun their noxious mud. 
Thus have 1 explained what will be found applicable to numerous cases of a 
similar nature • while it must be remembered in addition, that heat is necessary 
to the generation of malaria, and therefore, that many places and lands will pro- 
duce it in autumn, which would not have done so in spring. And if English phy- 
sicians, and the people also, forget or deny that their autumnal and summer fevers 
are the produce of this poison, it is not wonderful that they doubt or deny its 
existence ; while this dangerous and destructive error is confirmed by their simi- 
larly overlooking the visceral disorders, and the remainder of that long train of 
affectious which arise from the same cause, and which are most fully proved to 
arise from it by the unquestionable, and no less wide and severe experience of 
France and Italy. 
To proceed with similarly unsuspected places, I may name all kinds of ditches 
and drains, as these are constructed for agricultural or other objects. These are, in 
their very essence, marshes, and often of the worst quality; since often in a state 
of putrefaction which is more rare in a real marsh of any extent. And very often 
they are the real cause of the fevers which continue in a country after those oper- 
ations by which it has been drained ; as would easily he proved by a corresponding 
examination. To know this fact is, as in all other cases, to know the remedy, 
as far as that is in our power ; avoidance as the one generally most easy, and fur- 
ther attention to keeping them clean and free from weeds, — an attention not less 
required for agricultural reasons. And that such is their power in exciting dis- 
ease is proved, not merely by the experience of modem France and Italy, but by 
the remarkable fact that, in the times of ancient Home, perfectly informed at all 
times on this subject, such regulations formed a part of the laws, both as to these 
receptacles, and as to all canals. I need scarcely say that, in such cases, a clean 
earthern bank is the easy remedy ; as, in the case of ornamental waters, a stone 
margin is an effectual security — as far, at least, as the margins are concerned — since 
it is equally necessary to avoid the growth of sub-aqtiatie plants and the exposure 
of mud to the sun. 
I have thus described as minutely as I dare within these narrow limits, the 
chief places or forms of land and water which, as producing a living vegetation, 
are the sources of malaria; reserving what relates to remedial processes, to a fu- 
ture paper on this subject ; and I may now point out what remains, consisting in 
vegetable decomposition independently of vegetation. 
Among these, the sewers of towns are assuredly to he reckoned : and as I can 
take a proof from France without the hazard of offence, it is sufficient to mention, 
that the salpetricre was formerly subject to intermittent fevers, which attacked 
the inmates within the house; and that these being suspected to arise from the 
drains, these were closed up, with the immediate consequence of exterminating the 
disease. It is to he suspected that the object of the great cloacae of ancient Rome 
was the same, though their history has not reached us ; and it would be easy to 
confirm the same opinion, by the history of the diseases of the towns without end, 
and by that of their reforms on this point. Our own capital offers a striking 
example of the improvement of its health from this cause; while the history of 
Fleet-ditch is familiar. It had indeed been thought, and is still, that the fevers 
thus produced were typhus, or contagious fever : but while it is obvious that remit- 
tent or marsh fever will explain the effects equally, so must it he remembered 
that these fevers occurred in summer ; that they were peculiar to those particular 
vicinities; and that, from the reports of Sydenham and Morton, the fevers of 
London were of this very character. And the whole analogy of fevers produced 
by such repositories of putrefying vegetable matter, not altered as to its effects be- 
cause mixed with animal matter, seems to prove, as clearly as any thing can be 
proved, that these town-fevers, from this cause, are truly fevers from malaria, and 
not from contagion ; while the deception which considered them such, from occur- 
ring in the same houses or streets especially, is easily explained. It is just the same 
now as to rural situations ; and the errors are the same. The whole inmates of a 
house are affected with a fever, not because it is contagious, but because they have 
all been exposed to the same cause : while, unluckily, the occurrence of petechiae 
and so forth, in bad cases, assists in perpetuating the error ; as if this was not a 
common symptom in the marsh fevers of Italy, Holland, and France. 
