SummaryIn the 1940s a controversy developed between John H. Northrop (Nobel Laureate, 1946) and Max Delbrück (Nobel Laureate, 1969) on the formation of bacteriophage. From the historiography of molecular biology there emerges a picture of an obstinate Northrop who repudiated the ‘correct’ insights revealed by the experiments of Delbrück. The established reputation of Northrop confronts one with the question of why Delbrück's epoch-making experiments were not convincing for Northrop. It will be argued that this was a consequence of local incommensurability (...) between Northrop's physiological/chemical research style and Delbrück's bacteriological/genetic research style. The analysis of this controversy reveals the elements that made up these two research styles. (shrink)

This paper examines the vital role played by electron microscopy toward the modern definition of viruses, as formulated in the late 1950s. Before the 1930s viruses could neither be visualized by available technologies nor grown in artificial media. As such they were usually identified by their ability to cause diseases in their hosts and defined in such negative terms as “ultramicroscopic” or invisible infectious agents that could not be cultivated outside living cells. The invention of the electron microscope, with magnification (...) and resolution powers several orders of magnitude better than that of optical instruments, opened up possibilities for biological applications. The hitherto invisible viruses lent themselves especially well to investigation with this new instrument. We first offer a historical consideration of the development of the instrument and, more significantly, advances in techniques for preparing and observing specimens that turned the electron microscope into a routine biological tool. We then describe the ways in which the electron microscopic images, or micrographs, functioned as forms of new knowledge about viruses and resulted in a paradigm shift in the very definition of these entities. Micrographs were not mere illustrations since they did the work for the electron microscopists. Drawing extensively on primary publications, we adduce the role of the new instrument in understanding the so-called eclipse phase in virus multiplication and the unexpected spinoffs of data from electron microscopy in naming and classifying viruses. Thus, we show that electron microscopy functioned not only to provide evidence, but also arguments in facilitating a reordering of the world that it brought into the visual realm. (shrink)