This study examines some epistemological marks of the epidemiology's historical constitution, giving special emphasis to the process of scientific formalization (18th and 19th centuries). The reflection presented here tries to bring back, within the concrete development of the theoretical appre-hension of health's public space, the techno-social consubstantiation of the complementary and subordinate character, what nowadays charac-terizes the set of the epidemiological praxis. Relevant is the rationality's instrumental reduction, which stimulates and legitimates the epidemiological inference, made methodologically possible by the abstract concept of externai environment.