Geographical situation, together with certain vegetation, particularly of grounds which grow rice, is one remarkable for the production of endemic affections. But the soil which generates or gives force to the contaminating matter, is not alone the part where human beings feel its influence most severely. A low marshy ground, prolific of malaria, may be comparatively free; while some neighbouring elevated land, to which prevailing currents of air waft the volatile elements of disease, may be desolated by their virulent and concentrated action. "Malaria may be conveyed a considerable distance from its source, _and be condensed_ in the exhaled vapour, when attracted by hills or acclivities in the vicinity, and when there are no high trees or woods to confine it, or to intercept it in its passage." The inhabitants of the city of Abydos were at one time subject to disease, arising from malaria, generated in some neighbouring marshes; by draining these marshes, which suspended the growth of rank vegetation, the city became healthy. Rome is in like manner even now subject to fevers, having a similar origin. Sir James Clark says, "Among the more prevalent diseases of Rome, malaria fevers are the most remarkable, and claim our first notice." He considers the fevers to be of exactly the same nature as those of Lincolnshire {98} and Essex in this country, of Holland, and certain districts over the greater part of the globe. To the climate, the season, or the concentration of the cause of these fevers, he attributes their varieties. It is the same disease, he says, whether from the swamps of Walcheren, or the pestilential shores of Africa. From July to October the inhabitants of Rome are most subject to these affections. Sir James Clark further says: "It may be stated as a general rule, that houses in confined shaded situations, with damp courts or gardens, or standing water close to them, are unhealthy in every climate and season; but especially in a country subject to intermittent fevers, and during summer and autumn. The exemption of the central parts of a large town from these fevers, is explained by the dryness of the atmosphere, and by the comparative equality of temperature which prevails there."