CHAPTER V. ON THE PRESUMED SOURCES OF MALARIA.
§ 1. For all practical purposes, the fevers termed intermittent and remittent may be held to have their origin in one cause. Thus, whether on the marshy coasts of Essex and Kent, or the more dreadful banks of the Gambia and Niger, it is not improbable that the fever so destructive to European life is of one character—mild in Essex; fatal in Sierra Leone. But the fact is not to be overlooked, that when fever assumes an intermittent character, however it may conduce to the inefficiency of the population, it does not greatly swell the bills of mortality; on the other hand, the remittent form of fever constitutes that grand and hitherto insurmountable obstacle which Nature seems to have placed to the extension of the white man over the earth, excluding him, seemingly for ever, from the tropical regions of the world.
A favourite theory with medical men was, that the evil influence which causes fever, whether in Essex or on the Gambia, by the Scheld or the Niger, was a certain miasma produced by marshes more or less remote from human abodes; sometimes it was maintained that to produce the miasma these marshes must be in a great measure dried up, or in the process of being so; at other times an opposite opinion was held. These hypotheses were refuted, or at least much shaken, by Major Tulloch, in his invaluable “Statistical Report on the Sickness, Mortality, and Invaliding among Troops on the Western Coast of Africa” (p. 26). “So long as the fever continued to make its appearance during the rainy season, excessive moisture was deemed one of the principal causes, but that theory has been abandoned since it has, on three or four occasions, appeared and raged with equal violence in the middle of the dry season. If we attempt to connect it with temperature, the range of the thermometer offers equally contradictory results, the disease having originated and prevailed nearly as often when that was at the minimum as when at the maximum. Variations in atmospheric pressure afford no clue whatever to the solution of the difficulty, for here, as in all tropical climates, the fluctuations of the barometer are exceedingly slight. No definite connexion has ever been traced between the prevalence of any particular wind and the outbreak of the disease; the breeze blows over the same district in the healthy as in the unhealthy season. Besides, it seems entirely to negative the supposition that any of these can be more, perhaps, than mere accessories, when we find, from 1830 to 1836, the colony of Sierra Leone remarkably free from fever, without any perceptible change in these respects. It does not appear that the composition of the atmosphere during the prevalence of yellow fever in this command has ever been examined, to ascertain if it differed from what has usually been observed at periods comparatively healthy; but this test has been applied without any satisfactory result in other countries. Unless some light, therefore, can be thrown on the subject by a careful examination of the electrical state of the atmosphere at such periods, there seems little hope of the origin of this disease being ever distinctly traced to any appreciable agency—a circumstance which, except as regards the interests of science, is perhaps of less importance, since where the cause is so exceedingly subtle it would, even if discovered, be in all probability beyond human control.”[21]
In corroboration of the same views, amounting in fact to a rejection of the favourite hypothesis of the professors of the healing art—namely, that this fever originated in the miasma of marshes near the station, this careful and honest observer, whose merits as such have subsequently been fully tested in the celebrated Crimean inquiry, makes this further remark:—“The hypothesis that this fever originates from the miasma of marshes in the immediate vicinity of the station, as elsewhere it has been supposed to do, is directly opposed to the fact of the Isles de Loss, Acera, and the peninsula of Sierra Leone itself, being so subject to it, though all are in a certain degree remote from the operation of any such agency. If it be referred to similar exhalations wafted to the distance of several miles, how is its prevalence to be accounted for at Fernando Po, a mountainous region, and bordering on a mainland still more so, and where, so far as can be ascertained, no such agency is in operation? Instances of disease having raged with the same violence on the rocky Isles de Loss and the sandy wastes of Senegal, as in those parts of the coasts where vegetation is most dense, preclude the likelihood of it originating in a superabundance of that agency. In every description of situation along the coast has this scourge of Europeans been found to prevail. The low, swampy Gambia, the barren Isles de Loss, the beautifully-diversified features of Sierra Leone, the open and park-like territory around Acera, the lone, jungle-covered hills of Cape Coast Castle, and the rugged, mountainous island of Fernando Po, however different in aspect, have all exhibited the same remarkable uniformity in giving birth to the disease.”
It may, indeed, be objected that the fevers of Western Africa differ essentially from those traceable to the deltas of rivers, and to the lowlands alternately inundated and exposed to a high temperature, of more temperate climates; but I see no good reason in favour of such an opinion. The tables of sickness and mortality distinctly state that the fevers were intermittents and remittents, but mainly remittents, and that continued or ardent fever was scarcely present; whilst in Canada precisely the reverse is the case, intermittents prevailing to a great extent, remittents being comparatively rare. It would seem, however, that whether or not these fevers spring from a common cause, the temperature of the locality greatly influences the character of the disease.
It is impossible to deny the influence humidity has in engendering malarious tendencies, but it is not necessary that the humidity be to any great extent. Water is essential to life, it is essential also to the production of fermentation, of putrefaction; the absolute desert, as I have already remarked, is always healthy; so is the surface of the great ocean, which although it abounds with life, never putrefies, never exhales unpleasant odours. Countries, like some districts of Southern Africa and of Australia, where it seldom rains, are the healthiest countries in the world; there fevers of all types are nearly unknown, and the sufferers from such coming from unhealthy climates, recover speedily from the sad condition to which a residence in a tropical country and frequent attacks of fever may have reduced them. The Royal African Regiment, composed mainly of deserters, left the west coast of Africa for the Cape of Good Hope in 1817; many of them were so reduced in health as to be obviously unfit for service in any country where fevers of an intermittent or remittent character prevailed. Now, a residence on the frontiers of the colony of the Cape not only cured these fevers, but seems also to have been equal to the removal of those sequelæ of fever and dysentery which haunt those who have greatly suffered from them, bringing them in the end to an untimely grave. Nothing of the kind occurred in this remarkable country; all, or nearly all, recovered, and the mortality and sickness of this shattered corps, removed from Sierra Leone and the Gambia to the frontier districts of the Cape of Good Hope, fell considerably below what it is amongst the same class in Britain. These facts merit the attention of all interested in the welfare of the army of Britain, an army exposed more than any other to the effects of climate in all regions of the world.[22]
§ 2. The statistics I have just referred to may seem to some to shake all modern theories of malaria that have ever yet been offered to the public. I admit this to be the case; but I trust to be able to show that in the remains of animal and vegetable life, elements collected in the greatest abundance by the banks of rivers and lakes in marshy countries, near shores alternately exposed and covered by the tide, and especially in tidal rivers, but not exclusively in such localities, we have the source of that poison whose terrible effects on human life need not be enumerated here.
The result of Major Tulloch’s report in regard to the relative prevalence at different stations in British America of remittent and intermittent fevers, shows in a still stronger light the difficulty of establishing any uniform connexion between the presence of marshy ground and the existence of these febrile diseases, to which the exhalations from it are supposed to give rise; but they do not refute the view I take,[23] which is based on the researches of the profoundest chemists. As it was formerly shown that in some of the Ionian Islands, totally destitute of marsh and comparatively barren of vegetation, more remittent and intermittent fevers have been under treatment among the troops, than in others where these alleged sources of disease existed in the greatest abundance; so in the present Report we find it established, that yellow fever of the most aggravated form has repeatedly made its appearance in Ireland Island in the Bermudas, a rocky barren spot only a few hundred yards in breadth, “containing no marsh, and with little or no vegetation except a few cedar trees.”
“Conversely, again, we find that these diseases prevail to a remarkable extent along the banks of the lakes and the margin of the streams in Upper Canada, while they are comparatively rare in similar situations in the Lower Province; that among the troops at Fredericton, living on the marshy banks of a river, surrounded by a dense vegetation, scarcely a case of them is ever known; and that a similar exemption is enjoyed even by those at Annapolis and Windsor in Nova Scotia, though quartered at the embouchure of rivers daily subject to extensive inundations, and of which the banks, for the distance of several miles, exhibit that combination of mud, marsh, and decayed vegetation which is generally supposed a most prolific source of such diseases.
“When in subsequent reports we come to investigate the operation of these diseases on the west coast of Africa and other colonies, we shall be able to adduce still more satisfactory evidence on this subject; in the meantime we have felt it our duty to place the preceding facts in a prominent point of view, not for the purpose of establishing any particular theory, but to show how inadequate in many instances is the supposed influence of emanations from a marshy soil to account for the origin of these diseases. All the evidence obtained seems only to warrant the inference that a morbific agency of some kind is occasionally present in the atmosphere, which, under certain circumstances, gives rise to fevers of the remittent and intermittent type; and that though the vicinity of marshy and swampy ground appears to favour the development of that agency, it does not necessarily prevail in such localities, nor are they by any means essential either to its existence or operation.