[From contagion to transmission: a change in how epidemics are perceived].

The article contextualizes the various discourses that have sought to explain epidemics through the elaboration of different notions, concepts, and theories. It describes the circumstances under which these discourses appeared and were transformed and ties them in to each era's universe of knowledge. It analyzes (1) the perceptions of contagion and miasma that linked the spreading of epidemics to the senses of touch and smell; (2) the theory of epidemic constitution--a re-reading of the Hippocratic tradition; and (3) Fracastoro's 16th century theory of contagion. Special attention is devoted to elaboration of the concept of transmission in conjunction with the emergence of modern medicine during the 19th century and to the discontinuity occasioned by a new perception of how epidemic diseases spread.