exposure to the morning air in similar situations; the facts, as
they relate to the conducting of malaria, being the same, though the
meteorological circumstances are somewhat different. Hence, also, we
see why the grey mists which hang over wet grounds in the evening
in our own climate, are esteemed pernicious; the truth, however,
being, that they are perfectly innocent at certain seasons and in
certain places—as in the greater part of Scotland, for example, or in
those places and at those periods where malaria is not produced. The
distinction is valuable, because of the inconvenience of restrictions
on this subject, and because to know where the hazard really lies
is to reduce those, and also to prevent the infraction of rules by
not extending them beyond what is necessary; and thus also by seeing
what are the real dangers of what is called night air, we more easily
avoid them. Night air is avoided now, under a false philosophy,
because it is cold or damp, or for some other vague reason; while
the dangers from mere dampness or cold are as nothing compared to
those here pointed out; which also occur precisely where they are
least feared, namely, in warm summer evenings, after refreshing
showers, and so forth. Hence it is that fevers are produced in
summer, in rural situations, and especially perhaps amid the most
engaging scenery, by evening walks and exposure to what is naturally
considered, as it is felt to be, a balmy and refreshing sequel to
a hot day. Let this be enjoyed where it can with safety, and as it
often may; but such evening walks will not be safe in any of those
situations which I need not repeat here; after having detailed them
as I have done in the former paper. And lest I should be accused of
wishing to excite unnecessary alarm, I consider, on the contrary,
that it ought to be diminished by these remarks; because, if we
take the whole of [p044] England, there is perhaps not one acre in
a hundred thousand where there is danger from night air, or from
malaria in any mode; so that to distinguish where that lies, is to
have relieved from useless fears all those who may learn to make the
distinctions under review.
To pass from what relates to climate and season, and to proceed to
the propagation, simply, of malaria, it is almost superfluous to
say, that its influence, as to the production of disease, is much
regulated by proximity, which implies a state of concentration or
accumulation. Hence the danger arising from vicinity; while, as I
formerly remarked, where the generating source is small, this becomes
necessary to its effect, since dilution may be expected to destroy
the power of the poison.
For analogous reasons, its effect in the production of disease is
increased by concentration or condensation; and such a state of
things takes place in narrow and confined valleys, or in places
surrounded by woods, or in woods themselves; in any situation, in
short, where the poison is produced, and is so sheltered from winds
that ventilation becomes difficult. And if it is probable that this
is one chief reason of the peculiarly insalubrious nature of woods
and jungles in hot climates, so is it an universal remark in Italy,
that the short valleys in which the air cannot circulate are among
the most pestilential spots. And if this explains, also, in some
measure, the bad effects of calm weather, so does it account for the
unusually pestiferous nature of rivers and lakes confined within
wood, as are those of the tropical climates, and as there are many
also in different parts of Europe. That we ourselves are not exempt
from these additional causes of the influence of malaria, would be
easily shown by many references, were it not for the reason which has
caused me to exclude them.
It is another important question for practice, how far and in what
manner malaria can be conveyed by the winds to places where it is not
produced, so as to act in exciting disease. That it is conveyed to
certain distances by winds is amply proved by an abundant experience,
and I may first detail a few of the most useful particulars as to
this fact. In Italy and Greece, it is observed, that where long
valleys terminate on sea shores, on which the exits of the rivers are
swampy, it is an [p045] effect of the sea breeze, by crossing such
marshy ground, to convey the malaria up into the interior country,
to considerable distances, and to places which are in themselves
not insalubrious. Thus, also, does such a breeze, especially when
it is a warm wind, convey the poison up the acclivities of hills,
even to a considerable range of distance or elevation; a process
facilitated by the natural tendency of such winds to ascend. And as
a striking proof of this migration of malaria, it appears from Capt.
Smyth’s statistical account of the insalubrious villages in Sicily,
that out of more than seventy, about one-half are not seated near or
on lands producing this substance, but on acclivities, at varying
distances—thus receiving it through migration. The same is remarked
by Montfalcon of many towns in France; while in some, the place at
a distance is even more unhealthy than that which is immediately
situated in the marsh itself: and in our own country, this is equally
said to be true of the backwater at Weymouth, and of the marshes of
St. Blasey in Cornwall, acting more powerfully at some distance than
in the immediate spot.
With respect to the absolute distance to which the malaria can be
conveyed, it is yet an obscure circumstance, or at least the maximum
has not been fixed; but it is at least ascertained that the convent
of Camaldoli receives it from the Lake Agnano, at a distance of three
miles; while from certain naval reports, a distance of five miles has
been proved to permit its transmission,—and from an evidence that
cannot be doubted, inasmuch as it was the sudden breaking out of
fever in a healthy ship, anchored at that distance from the shore,
on the coming off of the land wind, attended by its peculiar and
well-known smell.
These facts are satisfactory thus far, and it would be abundantly
easy to add to them; but there is reason to suspect that it can
be conveyed to far greater distances, in certain favourable
circumstances: those reasons, in the first place, being derived from
certain meteorological analogies and considerations, and in the next
confirmed by experience. It is notorious that the ague appears on
our eastern coasts with the first east winds of spring; and while
this circumstance is most common on those of England, as for example,
in Kent, Essex, Norfolk, [p046] Suffolk, and Lincolnshire, it is
not thus limited, since it is known to happen further north, and
even in Scotland, where malaria is not indigenous to the soil. It
is very true that if we take any inland position in the places thus
noted, the natural solution is, that the malaria is generated in the
very soil itself of England, and merely propagated, perhaps even to
very moderate distances, through those winds. But the occurrence of
disease cannot be explained thus, when the place in question is so
situated that there is no land to the eastward, or when the breeze
is, most literally and rigidly, a sea breeze; while, when ague thus
occurs on the east coast of Scotland, where it is not produced by the
soil, it must be imported by the east wind.
These are the facts; while as malaria is not produced by the sea
itself in any known circumstance, though a vegetating sea beach
may give rise to it, we must seek the cause in lands far distant,
and consider this as a case of propagation of the poison from the
shores of Holland; and those shores are unquestionably competent to
that effect: so that the only question that remains, the fact being
admitted, is, whether, _à priori_, or theoretically, such a view is
probable, or whether it is consistent with those physical principles
that are concerned in the propagation of malaria.
I am aware that such a view will excite the incredulity of those
who have not attended to this subject; though it appears to me that
it comprises nothing averse to our knowledge of the philosophical
circumstances concerned. In the first place, let us remark that the
east wind, and particularly the east winds of spring, are notorious
for their moisture, and that a moist air is the best conductor of
malaria, as moisture in the air, under the form of evening mists, or
in other modes, appears even to be its proper vehicle, or residence,
if I may use such a term; and though I have not as yet separated
the case of a fog, I may now remark, that the effect in question,
or the production of agues by fogs arriving from the sea, is even
more notorious than their generation by an ordinary clear wind. So
notorious and popular, indeed, is this fact, that the fog itself is
deemed the source of the disease, as the east wind under any form is,
in other circumstances; while I hope it will even now appear, [p047]
that the real cause lies in the malaria transported or conveyed
by those winds or fogs, and of which they are the true and best
repository and vehicle.
And these are the reasons for thinking that the malaria, with the
wind, may be transported to a distance as great as that which the
present view requires; most easily perhaps in a fog, but without
difficulty even in a clear wind. It is remarkable that the east wind,
as it is the most persevering, is that one also which preserves the
most steady horizontal and linear course. I have also shown, in a
former work, that it is a property of winds to travel in distinct
lines through a tranquil atmosphere, and often in streams of a very
limited breadth; that opposing streams will also move, in absolute
contact; and that even rapid streams of wind will cross each other’s
courses without difficulty. This proves that, in any such stream,
there is a principle of self-preservation or integrity, and renders
it probable that the several portions retain the same relative places
to each other, at any distance, during the career of the whole; and
there is a proof of this afforded in the fact of those columns or
streams of insects which are brought over by such winds, and very
frequently from those very countries, or from Holland and Flanders,
in the most regular order, or without disturbance or dispersion.
Hence it may be argued, that if a malaria, generated any where
and conveyed by the winds, can be transported to a distance of
three miles, as has been proved, there is no reason why it should
not travel much farther, or to any distance that can be assumed:
and if this be true of a clear wind, the case of a fog is even a
much stronger one; since there is little reason to doubt that the
individual parts of such fog, in any assumed mass, will retain their
relative places to each other, as perfectly after a journey of any
given number of miles, as they did at the point of production; and
if a portion of malaria has been united to a portion of fog, in the
marsh which produced both, or whence both have come, there is every
apparent reason why it should be found in that same portion at any
farther or assumed distance, because there is no cause for either its
dispersion or its decomposition.
A fog is a cloud, simply; and it is notorious that a single [p048]
cloud, and often of very small dimensions, will remain at rest
in the atmosphere, or travel very many miles without the loss of
its integrity; however we may imagine it assailed by the various
meteorological causes of destruction, as well as by mechanical
violence. This in itself proves the consistency with which a current
of wind preserves the relative positions of its integral parts;
because it is plain that a disturbance among these must disturb or
destroy the cloud which, in reality, forms a portion of that current,
as a gaseous body: and since that cloud is a mist, since it might
have been the very evening mist embodying a malaria, and since it
is its real vehicle and repository, it is plain that had it, or
any individual cloud, contained such a portion of malaria, it must
have had the power of transmitting that, and would actually have
transported it to any distance to which itself might travel. Thus, it
is evident, may a fog, generated in Holland, carry without difficulty
to the limits of its range, or to the coast of England, that malaria
which became entangled with it at its birth-place or in its passage;
and thus, I have little doubt, is the fact of those agues explained,
and this transportation to such distances established.
I cannot, at least, conceive any demonstration as to facts of this
nature more convincing, nor anything wanting to the proof; while
I may proceed to make some remarks on the east wind, and on fogs,
simply, because they concern this question.
The proof that it is a malaria in the fog, and not the fog itself,
which is the cause of disease, is evinced by the following fact;
while it ought surely to be unnecessary to say, that if fog alone
could produce such fever, water itself must be the poison: since a
fog is a cloud, and its constituents, when pure, are only atmospheric
air and water. No intermittents are ever produced on the western or
northern shores by the sea fogs, and for the plain reason, that there
is no land whence they arrive. The clouds of mountainous regions
do not produce fevers, though these also are fogs; and what forms
a most absolute proof of this is, that in Flanders, it is the fogs
which come with a southwest wind, or the southerly winds themselves,
which transport and propagate malaria and disease; while; as soon as
the winds shift, and blow from the sea, the fevers [p049] disappear,
though those particular winds are so charged with fog, as to darken
the whole country for days: and it will be found an invariable rule
all over the world, that when a fog is the apparent cause of disease,
or when an east wind is such, it is because these have been generated
in a land of marshes, or have traversed one; and that, under other
circumstances, or where no pernicious land lies in the way, they are
as innocent as any other fogs and winds, and that the hazard and the
suffering will arise from those, be they whatever they may, which
traverse pestilential lands.
But I must defer this particular and interesting subject to another
occasion, lest I make this article too long; and proceed to examine
some other circumstances connected with the transportation of malaria.
First, however, I must notice one fact as to this transportation from
Holland, partly because it is a necessary fact in the history of
malaria, and partly because it might be used as an argument against
the view which I have just given. The east winds of autumn are not
supposed to bring remittents, as those of spring bring agues, though
I cannot assert that this is absolutely true. Being assumed, the
solution is easy. If the winds of this nature in spring, are notedly
moist, and thus vehicles of malaria, the case is exactly the reverse
with the east winds of summer and autumn; or as the east wind may
be the most moist of winds, so may it be the most dry; while it is
a consequence of its extreme dryness, in fact, that it is always
the very cause of our burning summers. This is the history of our
last summers, and it is invariable, whether as it relates to seasons
or single days; and it is plainly owing to its permitting the more
ready transmission of the sun’s rays. That it is the very harmattan
of Africa, it is almost unnecessary to say; and as dry wind is not
a conductor of malaria, as that poison is in fact decomposed or
destroyed in these circumstances, daily and invariably, it is easy to
see why the remittents of Holland should not be transported, like its
intermittents, though even this may possibly happen under particular
circumstances.
To proceed; and to the next remarkable facts connected with the
propagation of malaria.—The most singular of these is its limitation,
or that yet unexplained property by which it is [p050] determined in
a particular direction, or confined to a particular spot, while it is
a piece of knowledge of some practical value. There is an appearance
of incredibility about many of these facts, and, accordingly, they
have not only been disbelieved but ridiculed, although nothing in the
whole history of this substance is better established.
With respect to direction, in the first place, it is remarked in
Italy, currently, that this poison will enter the lower stories of
houses, particularly with open windows, when the next above escape;
and hence, in many places, no one ventures to sleep on ground floors:
and the truth of this was confirmed in the barracks at Jamaica by Dr.
Hunter; as the cases of fever occurring among the men in the lower
rooms much exceeded those which happened in the upper ones. But I
am also informed, that in some places in Norfolk this peculiarity
is reversed; or that there are houses where it is remarked that the
ground-floors are safe, while no one can sleep in the upper stories
without hazard.
That malaria may in some manner be attached to the soil is also well
known by its effects, and especially in Italy. There it is remarked
that it is extremely hazardous to cut down certain bushy plants which
appear to entangle it, and that fevers are a frequent consequence of
such carelessness. Thus, also, does fever seize on the labourers who
may incautiously sit down on the ground, while they would escape in
the erect posture; being thus, indeed, sometimes suddenly struck with
apoplexy, which is one of the effects of this poison, or even with
death.
It has similarly been observed that it is often retained in the
shelter of drains, or in the ditches of fortifications; whence
frequent fevers among the sentries on particular guards, when the
other soldiers escape. And thus was it even proved at Malta, that it
was transported from the sea-shore, and thus lodged in a dry ditch of
the works at Valetta; all these facts being possibly to be explained,
by supposing it possessed of a greater specific gravity than the
atmosphere, or else attached to vapour thus weighty, exhibiting
effects analogous to those which carbonic acid displays in the
Solfatara.
But the circumstance most difficult of explanation is, that in
Rome, and numerous places in Italy, and even where it is [p051]
transported from a distance by the winds, not generated on the spot,
it is found, perennially, and through the whole course of successive
years, to occupy certain places, and to avoid, as constantly, others
quite near, and, as far as the eye can judge, equally exposed, and
in all respects similar. Thus, one side of a small garden, one side
of a street, or one house, will be for ever exposed to disease, or
uninhabitable, when, at a few feet or yards distant, the very same
places are as constantly free of danger: and thus it was found at the
village of Faro, in Sicily, that all the troops of our army quartered
on one side of the single street which formed it, were affected
by fevers, and suffered great mortality, while those on the other
remained in health.
But the most remarkable case of this nature known to me, is a
domestic one, and which rests on the testimony of thousands of
persons, or of the whole country, however incredible it may appear.
It is, that between Chatham and Brighton, including every town and
single house, and Sittingbourne among the rest, the ague affects the
left hand side of the turnpike road, or the northern side, and does
not touch the right side, though the road itself forms the only line
of separation.
We cannot as yet conjecture the cause of this very singular
circumstance or property, at least in cases of this nature;
though, under certain events of this kind, there are some facts
in meteorology that may offer a solution. These are the notorious
ones, that a hoar frost, or a dew, will sometimes be found most
accurately limited, both vertically and horizontally, by a definite
line; stopping, for example, at a particular hedge, and reaching to a
certain altitude on a tree: but for the other cases, we must yet wait
for a period of more accurate knowledge as to this singular substance.
There is now one circumstance of importance, relating to the
destruction or decomposition of malaria, which must not be passed
over, from the interest of the facts depending on it: this is,
that its propagation is checked by the streets of a crowded town,
and apparently owing to this very cause, decomposition. Thus it is
observed, that the fever never appears in the Judaicum of Rome, and,
similarly, that the crowded streets and the poor people escape, when
the opulent houses and open [p052] streets are attacked; and hence
the Villa Borghese, among many other palaces and opulent houses
in Rome, has been abandoned, while such desertion, being limited
exclusively to houses where the air is most open and free, naturally
excites wonder: the cause, however, is now plain; and thus it now
appears why it was that the Penitentiary in Westminster suffered
formerly from dysentery, originating in this cause, when no such
disease appeared among the neighbouring inhabitants.
And if this fact is of value as it may relate to the erection of open
streets in any place of this nature, it is most important to point
out what has been the continuous effect at Rome, as the ultimate
consequences threaten to be extremely serious.
It appears that from cutting down some forests which many years ago
occupied the declivities of the hills to the southward of Rome, the
malaria was let in upon that city from the Pontine marshes; and,
further, that the extirpation of a similar wood to the eastward had
let in the same poison upon another quarter. Thus it has been found
to enter the city through the Porta del Popolo, while, for many
years past, it has been gradually extending its influence through
the streets; leading annually and successively to the abandonment of
many houses and palaces, and still annually increasing and extending
its ravages; so as, at length, as I understand, to have even
become sensible at the Vatican. And the lines which it follows are
distinctly traced out by the inhabitants; while, as I have already
said, it is only the houses of the opulent which suffer, further than
as the abandonment of these may also influence the inferior ones in
their neighbourhood.
Whatever the original cause may be, and however the direction,
abstractedly, may be regulated by the winds and the forms of the
streets, or by local and fixed circumstances, it is plain that the
annual extension is the consequence of desertion, and that as the
inhabitants retire from before it, it acquires the means of making
a new step and a further progress; because thus they withdraw
those fires and smoke, or whatever else it be, dependent on human
crowds, which decomposes and destroys this substance. And hence it
must follow, that as Rome shall become still further abandoned and
depopulated, from want of industry, or from political feebleness
[p053] added to this cause, the effects must be expected to increase
in a sort of geometrical ratio; almost leading to the fear that
the whole city itself may, in time, fall a victim to it, or become
abandoned to the wolves and mosquitoes.
If I dare not inquire more minutely into the remaining circumstances
connected with the propagation of malaria, lest I should extend this
article to an inconvenient length, it is necessary now to offer
some remarks on prevention, and especially as it relates to this
circumstance—the propagation of the poison; since the rules for
prevention, as far as this relates to production, may be deduced from
what was said in a former paper on this subject, and relate chiefly
to the drainage of lands, and to other practices, more or less
obvious, which a little reflection will, without much difficulty,
deduce from what was there said.