_Causes._ It was formerly ascribed to improper hygiene, chills, cold rain storms, night dews, hoar frost, malarious emanations, putrid, stagnant or iced water, irritants in food, green, fermented or musty food, a too liberal diet after starvation, overtaxation in very hot weather, and bad odors from decomposing carcasses. These can only be accepted as predisposing causes begetting a general debility, or debility of the alimentary canal and laying that open to the attacks of specific microbes. The close aggregation of cattle on ship-board, in besieged cities, and in the parks of armies in the field, has apparently contributed to the propagation of the dysentery. The removal of a victim to a herd with free healthy range seldom starts a new center of the disease. In all infected herds huddled in small compass there is every facility for the propagation of a germ already present, and especially in the commissariat of a belligerent army there are enough privations, over-exertions and other trying conditions to favor predisposition. Faulty food like stale bread, musty hay, have been supposed to cause it. For man and beast alike dysentery is preëminently a disease of the tropics, and of hot seasons, and will often subside on the advent of cold weather. Its propagation on given (swampy) soils, and in particular (foul) stables strongly suggests a special germ, though for the cow this has not been perfectly identified. Gerlach vainly attempted to inoculate it, and it does not often propagate itself beyond the foul and infected localities or stables, yet its persistence in them for years bespeaks unequivocally the operation of a special pathogenic ferment. It may also be fairly assumed that it is not necessary that the same factor should be present in all cases alike, but that one operates predominantly in one case and another in another. In other words dysentery must be recognized as not one disease, but several, of which the true pathogenic microbes have not yet been fully demonstrated, but which are classed together because of the similarity of the attendant lesions.