The progress of medical bacteriology after 1880 was extraordinarily rapid, its most conspicuous accomplishment being the identification of the microbial agents of numerous severe and socially disruptive communicable diseases. The new knowledge was potentially useful knowledge and application of bacteriological understanding and techniques began almost immediately. An important field of application was the study of the movement of disease through an afflicted human population. This was the traditional territory of epidemiology. Often combined in a single person, the epidemiologist-bacteriologist attempted to exploit diverse aspects of the germ theory of disease, having recognized clearly the unique promise of a rigorous scientific foundation for long-standing public-health concerns. The focus of this proposal is historical study of the interaction between epidemiology and bacteriology in the years when both were essentially new sciences, ca. 1850-1900. The work is structured about the foremost exotic epidemic disease of the era, Asiatic cholera. Robert Koch and his associates in Berlin took the lead in bacteriological inquiries, attending to cholera especially between 1883 and 1894. Already, however, Max von Pettenkofer, working in Munich, had laid firm foundations for a predominantly environmentalist view of the disease, stressing air, water and, above all, soil. Over many years a fierce revalry continued between the seemingly irreconcilable biological and environmentalist interpretations of cholera, with a relatively clear decision coming only with the dreadful Hamburg epidemic of 1892/1893. This study will show how laboratory science was introduced into field investigation and exhibit the nature of the hygienic measures proposed and imposed as a result of these inquiries. Central issues include the importance of early and confident diagnosis, the notion of the healthy carrier, the restructuring of public institutions and administrative powers to accommodate new technical procedures and the creation of popular support for the enterprise. This study constitues part of the applicant's goal of preparing a history of modern epidemiology, emphasis falling on the innovative years between 1840 and 1910.