"Whether or not you can observe a thing depends upon the theory you use. It is the theory which decides what can be observed." - Albert Einstein

Entstehung und Entwicklung einer wissenschaftlichen Tatsache (Genesis and Development of a Scientific Fact; 1935), analyzed the origins of the Wassermann test for the detection of syphilis. This test, Fleck argued, was not the work of a solitary genius but reflected the coordinated efforts of thousands of researchers. The basic unit of production of scientific knowledge is a “thought collective”—a group of scientists that shares the same “thought style,” acquired during a long process of learning and socialization. Scientists perceive natural phenomena through the prism of the “thought style” of their community, that is, through a specific set of concepts and practices. “Scientific facts,” therefore, cannot be dissociated from the methods used to display them.
Source: Löwy, Ilana. 2010. Fleck, Ludwik. YIVO Encyclopedia of Jews in Eastern Europe. (accessed October 3, 2012).