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.