Kuhn refers to the book Ludwik Fleck: Entstehung und Entwicklung einer wissenschaftlichen Tatsache, 1935/reprint 1980 (Frankfurt: Suhrkamp) In the introduction of his "The Structure of Scientific Revolutions" Kuhn quotes Fleck. However, a comparison between both works shows how much of Kuhn was already prethought in Fleck. Dieter Boegenhold