In 1905 two different etiologic agents for syphilis were proposed in Berlin, one, the Cytorrhyctes luis, by John Siegel, the other, Spirochaete pallida, by Fritz Schaudinn. Both scientists were pupils of Franz Eilhard Schulze, and were outsiders to the Berlin medical establishment. Both belonged to the same thought collective, used the same thought style, and started from the same supposition that the etiologic agent of syphilis must be a protist. Both used the same morphological approach, the same microscopes and the (...) same stains. Both presented their findings in the same societies, used the same rhetoric, published in the same journals, used the same arguments to criticise each other's shortcomings. Both were backed by powerful institutions and enlisted the support of prestigious patrons. Within half a year, the scientific community at large had in its overwhelming majority accepted Schaudinn's results and rejected those of Siegel. Social forces thus cannot be shown to have played any role in deciding the issue. Ludwik Fleck's suggestion that 'appropriate influence' and a 'proper measure of publicity throughout the thought collective' would have been sufficient for Siegel's ideas to win the day is untenable. (shrink)