[Scientific facts and their public: the history of the diagnosis of syphilis].

In the 1910's and 1920', thanks to the conjunction of scientific views concerning the specificity of anti-bacterial antibodies, of lay ideas about the existence of anti-bacterial antibodies and of the perceived importance of developing a syphilis test for public health officials, the community of serologists collectively transformed a relatively inefficient diagnostic test described by Wassermann in 1906 into an "incontestable scientific fact". This "scientific fact" established the equivalence: Wassermann positive individual=person infected with the germ Treponema pallidum, the etiological agent of syphilis. It modified the boundaries of the nosologic entity "syphilis", medical practices, professional attitudes, lay perceptions of syphilis, and health policies. In the 1950's, however, discrepancies between Wassermann test data and epidemiological data and, on the other hand, the development of specific anti-treponemal tests, destabilized the previously stabilized "scientific fact". A high percentage of Wassermann positive individuals were redefined as "biological false positifs", that is persons who suffered from chronic affections able to induce positive results of the Wassermann test. The equivalence Wassermann positive person=individual infected by Treponema pallidum was replaced by the equation: Wassermann positive person=individual infected by Treponema pallidum or biological false positive. The new perception of the Wassermann test again changed scientific views, professional practices and lay beliefs. The history of the Wassermann reaction illustrates the complicated interaction between "scientific facts" and "social facts", and the mutual shaping of both.