"In considering the circumstances external to the residence, which affect the sanitary condition of the population, the importance of a general land-drainage is developed by the inquiries as to the cause of the prevalent diseases, to be of a magnitude of which no conception had been formed at the commencement of the investigation. Its importance is manifested by the severe consequences of its neglect in every part of the country, as well as by its advantages in the increasing salubrity and productiveness wherever the drainage has been skillful and effectual." La Roche calls attention to these facts:—That the acclimated residents of a malarious locality, while they are less subject than strangers to active fever, show, in their physical and even in their mental organization, evident indications of the ill effects of living in a poisonous atmosphere,—an evil which increases with successive generations, often resulting in a positive deterioration of the race; that the lower animals are affected, though in a less degree than man; that deposits of organic matter which are entirely covered with water, (as at the bottom of a pond,) are not productive of malaria; that this condition of saturation is infinitely preferable to imperfect drainage; that swamps which are shaded from the sun’s heat by trees, are not supposed to produce disease; and that marshes which are exposed to constant winds are not especially deleterious to persons living in their immediate vicinity,—while winds frequently carry the emanations of miasmatic districts to points some miles distant, where they produce their worst effects. This latter statement is substantiated by the fact that houses situated some miles to the leeward of low, wet lands, have been especially insalubrious until the windows and doors on the side toward the source of the miasm were closed up, and openings made on the other side,—and thenceforth remained free from the disease, although other houses with openings on the exposed sides continued unhealthy.