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666 proliferation is the papilla, which becomes very much swollen, and the Malpighian layer.

Diagnosis.— A painless, insensitive, larger or smaller, circular, encrusted, red granulomatous excrescence occurring in the endemic district is almost certainly yaws. The most important point in connection with yaws, both as regards diagnosis and etiology, is its relation to syphilis. It has been held by some distinguished authorities— Hutchinson, for example— and is still maintained, that yaws is syphilis modified by race and climate. Certain features which the two diseases have in common are pointed to, and, doubtless, the discovery of a spirochæte in association with both diseases will be adduced in support of this contention. So far as clinical and microscopical evidence goes, it is decidedly in favour of, not to say conclusive for, regarding the two diseases as specifically distinct. There are many points of contrast in their clinical features. I may mention the primary sore, the infection of the foatus, the adenitis, the exanthem, the alopecia, the absence of itching, the iritis, the affection of the permanent teeth, the bone and eye affections, the congenital lesions, the polymorphism of the eruptions, the nerve lesions and the gummata of syphilis. All these are wanting in yaws. Moreover, both diseases may concur in the same individual (Powell cites two cases, and Charlouis two, of syphilis supervening on yaws); and antecedent syphilis certainly does not confer immunity as against yaws, nor antecedent yaws against syphilis. The serum of both diseases gives a positive Wassermann reaction. Monkeys inoculated with yaws are not absolutely immunized against syphilis, but Prowazek found under experimental conditions that inoculation of the spirochæte of yaws conveys a relative immunity to a subsequent syphilitic infection, and that monkeys were less susceptible to syphilis after a previous attack of yaws. Yaws may die out in a community, as in British Guiana (Daniels), yet syphilis remain; yaws may be universal in a community, as in Fiji and Samoa, and yet true syphilis, whether as an acquired or a congenital