§ 1. Although the amount of disease and mortality traceable to accidents, to the ordinary atmospheric changes of which the thermometer gives us due information, to the habits of life and the effects of hereditary influence, be sufficiently great, it yet seems nothing when compared with the terrible inflictions occasionally and at uncertain periods visiting man, whether shut up, as it were, within the confined haunts of cities, or living apart in the open country, in situations where it might be reasonably imagined no such influences could reach him. The poison of typhus, for example, if it be a poison, spares none: in certain epidemics the citizen and the peasant suffer alike: the strong robust man in the prime of life is its special victim; cholera attacked the inhabitants of the remote and isolated cottage as certainly as the careful wealthy citizen, and with the same results. No mode of life, nor sex, nor age was security against it; no race, no locality.[45] An inquiry into the origin of such influences is the most important to which man’s attention can be directed. These terrible epidemics appear under various forms; sometimes it is by typhus or influenza, cholera or plague; even those diseases which seem to be endemic, or confined to a locality, assume the form of epidemical raging pestilences, and then disappear for a time. Thus the remittents and yellow fevers of tropical climates do not always put out their whole strength; there is a lull, a season of repose, when man, deluded by the security of a few years, hopes that at last the evil influence has disappeared for ever. Vain hope! It moves in cycles, like the typhus of temperate climates, falsifying all predictions. Thus, in Jamaica, the grave of so many noble English regiments, the fever, sometimes called remittent, sometimes yellow fever, exhibited its fitful attacks during eighteen years, in the following capricious manner, at a station called Port Antonio, about eighty miles from Kingston. At Stoney Hill Barracks, the disease was still more capricious.[46] As the poison producing intermittents and remittents must be presumed to be always present, it is incomprehensible how it should at times cease its attacks on man, showing that another influence or element requires to be present to render its attack successful. Again, we find that within a limited range, a long residence in a land unhealthy to the stranger seems by acclimation to diminish if not entirely to eradicate the susceptibility to disease on the part of the latter; but this opinion must be received cautiously and with reserve, for the phenomenon may be partly due to the difference in race, respecting which we as yet know but little. The banks of the Scheldt, the Polders of Holland, and the mouths of the Rhine, the Danube, and the Indus, are healthy to the natives of these districts; graves to foreigners. In all inquiries of this kind, these well-established facts must not be overlooked.