The ravages wrought by epidemics in Iran as of 1821 acted as a stimulus to medical thought while the awakening of political consciousness mobilized efforts to fight contagious diseases. The combination "epidemics-politics-medicine" made nineteenth-century Persia turn to European science for help. Thus western medicine was introduced into Persia. If this introduction has been perceived by political means and epidemiological justification, the theoretical and epistemological process involved has been almost completely overlooked or misinterpreted. It is generally considered that the imported medicine swept away the local one, but this is not altogether true. It was the internal evolution of traditional medicine which paved the way for anatomoclinical medicine. This evolution comes accross clearly in the works of Shirâzi and Sâveji between 1831 and 1862, years in which epidemics struck frequently and violently. While Europeans in Iran such as Dr. Polak qualified heyzeh (a kind of severe diarrhea) a "sporadic cholera" or "autumn cholera", Shirâzi wrote three treatises to show that heyzeh was not cholera but an ordinary kind of diarrhea caused by generalized malnourishment. Shirâzi was also an innovator in the theoretical and terminological fields, doing away with the notion of vabâ which meant a putrid atmosphere. Vabâ became a physiological anomaly which took on epidemic proportions in an impure atmosphere. The modern definition of vabâ meaning cholera was therefore elaborated thanks to Shirâzi.