in shady and windless places, as in thick jungle or in a dark room. A very few species are diurnal in habit.
Disturbance of the soil.—— It has often been observed that in malarious countries, so long as the soil remains undisturbed, agues and the severer forms of fever are comparatively rare; but so soon as building, road-making, and other operations implying soil disturbance commence, then severe malarial fevers appear. After a time when, in the progress of events, these operations have concluded, and the broken surface of the soil has, so to speak, skinned over again, the place becomes once more comparatively healthy. The medical history of Hong Kong may be cited in illustration of this fact. At the commencement of the occupation of this island by the British, for a short time it was healthy enough. Then, on its cession being completed, and when barracks and houses were being built and roads laid out, it became excessively unhealthy, the soldiers dying by the hundred of pernicious fevers. In time the sickness and mortality gradually decreased; and now, so far as malaria is concerned, the city of Victoria is healthy. But, even at the present day, wherever in the outskirts, in the course of the construction of houses, roads, forts, and similar works, soil is turned up, fever—— often of a most pernicious type—— is nearly sure to break out among those engaged in the works. I cite the case of Hong Kong; but there are dozens of other instances which might be quoted, and which are quite as apposite and convincing, as to the danger of carelessly disturbing the soil in malarious localities, particularly during the warm season. Soil disturbance usually implies the formation of holes. Holes imply puddles, and puddles imply mosquitoes. Workmen from many districts, some of them malarious, are assembled in crowded lodgings; one infected workman suffices to start the epidemic. In the present state of knowledge this seems to be adequate explanation of the recognized danger of earth-cutting in malarious dis- tricts.
