The microscopist of modern life.

This is an essay in the history of observation of the natural and social worlds. It explores how nineteenth-century Paris became a field and object of scientific observation and how the everyday lives, and even the health, of scientists living in the city and leaving the city for the "country" modeled observations and theoretical interpretation. The story concerns the first important work in the research school of Louis Pasteur to focus on a human and urban disease, diphtheria, rather than animal and rural ones. An urban field practice emerged from characteristically Parisian forms and literary fictions of street life and public space, leisure, spectacle, and crowds. Some of these, such as transcience, were (and still are) viewed as not only characteristic of "modern life," but also the source of new practices and sensibilities in painting and literature. Microbiological studies elsewhere --such as in New York and Hamburg--were based on very different urban structures, patterns of everyday life, national cultures, and aspects of modernity.