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XXXVI] practised by our ancestors, although identical with it in principle— the disease is rapidly dying out.

Apart from Egypt, we know nothing of the early history of leprosy in Africa. We are equally ignorant as regards aboriginal America. The historians of the Spanish Conquest do not allude to it as a native disease; we appear, therefore, to be justified in concluding that the introduction of leprosy into the New World was probably effected by the Spaniards, or through the negroes in the days of the slave trade.

Rise of modern knowledge of leprosy.— The more important landmarks in our modern knowledge of leprosy are, first, the publication in 1848 of Danielssen and Boeck's "Traité de la Spedalskhed," in which, for the first time, the clinical features of the disease were carefully and critically described; second, the descriptions of the macroscopic and microscopic lesions —the leproma, the nerve lesions, and the lepra cell— by Virchow, Vandyke Carter, and many others; and last, the discovery in 1874 by Armauer Hansen of the specific cause of leprosy the Bacillus leprœ —a discovery which brings this disease into line with tuberculosis, and has given a much- needed precision to our ideas on the important subjects of heredity and contagion, and on other practical points bearing on the question of the leper as a source of public danger and on his treatment and management.

Geographical distribution.— Whatever may have been the case formerly, at the present day, with unimportant exceptions, leprosy is a disease more particularly of tropical and sub-tropical countries. So generally is it diffused in these that it would be more easy to specify the tropical countries in which leprosy has not, than to enumerate those in which it has been ascertained to exist. Moreover, it is probable that in many of the countries not yet positively known to harbour the disease it does really exist; for experience show that the endemic area of leprosy enlarges as our knowledge of the natives of the uncivilized regions of the earth becomes more intimate. It may be safely concluded,