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XXXVI] may be said of occupation, and social and hygienic conditions in general. Very probably bad food and bad hygienic circumstances have in this, as in most germ diseases, a predisposing influence but they certainly cannot create a lepra bacillus and leprosy, any more than they can create an acarus and itch. This is abundantly, shown by the absence of leprosy at an earlier period in countries in which, without alteration in the food or other hygienic conditions, the susceptibility of the natives to the disease was subsequently proved by its rapid spread on being introduced from without, e.g. the Sandwich Islands and New Caledonia; and also by the disappearance of the disease, in other instances, under the influence of the segregation and isolation of lepers, without any concurrent material alteration in food or other circumstances, e.g. Scotland, Ireland, and most European countries. Sir Jonathan Hutchinson very sagaciously and truly remarked that leprosy is more especially a disease of semi-civilization. Savages are exempt; the highly civilized are exempt; but when the savage begins to wear clothes and live in houses he becomes subject to the disease. In other words, in the early stages of civilization opportunities of infection are multiplied, and their influence is not counteracted by cleanliness of house or person. Climate.— Climate can in no way be considered a cause of leprosy, for leprosy exists in all climates and in all latitudes. But it does seem to have some influence in determining, to a certain extent, the type the disease assumes. It would appear that the nodular form is more common in cold, damp climates; the nerve form in warm or dry climates. The lepra bacillus.— Hansen remarks, "There is hardly anything on earth, or between it and heaven, which has not been regarded as the cause of leprosy." However true this remark may be as regards times prior to Hansen's discovery, we are now practically certain that the lepra bacillus is the cause of leprosy. The only gap in the evidence, otherwise conclusive, lies in our present inability to convey with certainty,