Iconic accounts of the "bacteriological revolution" presented it as a radical change in the understanding of the natural world. Scientist had discovered that human being shared their environment with billions of invisible living beings which shape life phenomena, health and disease. They also learned to cultivate and manipulate these invisible creatures. The domestication of microorganisms in the laboratory disarmed them as enemies and occasionally transformed them into allies. This analysis of the development in French bacteriology displays a more nuanced and complex picture, with continuities as well as ruptures, and multiple levels of change. Between 1880 and 1900, the rise of "pasteurian science" did produce important changes in French society, but these changes were obtained through a variety of approaches: introduction of new experimental techniques, administrative and legal methods, training of professionals, education of the general public, and a direct political intervention.