The rediscovery in the mid-1970s of Ludwik Fleck's initially neglected monograph, Entstehung und Entwicklung einer Wissenschaftlichen Tatsache, published in 1935 and translated in 1979 as Genesis and Development of a Scientific Fact, has resulted in extensive, still ongoing, secondary writings, mainly within the humanities. Fleck has been interpreted as furthering a relativistic conception of science. Nowadays, he is often viewed as an important contributor to contemporary sociology of science and a forerunner to Thomas Kuhn. Fleck's account of the Wassermann reaction, (...) which forms the basis of his epistemology, has been praised as developed by a scientist well acquainted with the field in question. Because of the scarcity of available material on Fleck, however, the question of his sources has remained an unsolved issue. In the present article, an alternative reading is suggested. By focusing on the scientific content of the monograph, mainly neglected in the modern interpretations of Fleck, and on the so far overlooked sources of his writings traced back to their German origin, a better understanding of Fleck's account of the Wassermann reaction can be given. The consequences of this alternative reading for the conception of Fleck's monograph and for the impetus of his mission are discussed. (shrink)