The book Genesis and Development of a Scientific Fact, written by Ludwik Fleck in the early thirties and which remained practically unknown for a long period, is considered today, following its recent rediscovery (mainly in relationship with T. S. Kuhn's book The Structure of Scientific Revolutions ) to be an important pioneering work in the sociology and in the epistemology of the natural sciences. Fleck was the first to developed in detail the view that in the natural science facts do not derive automatically from the observation of nature, but are socially constructed and, as such, dependent on the socio-cultural context, the "thought-collectives' in which they evolved.