Text Box: Epidemiology John Snow, a London physician, was among the first to use anesthesia. It is his work in epidemiology, however, that earned him his reputation as a prototype for epidemiologists. Dr. Snow’s brief 1849 pamphlet, On the Mode of Communication of Cholera, caused no great stir, and his theory that the city’s water supply was contaminated was only one of many proposed during the epidemic. Snow, however, was able to prove his theory in 1854, when another severe epidemic of cholera occurred in London. Through painstaking documentation of cholera cases and correla¬tion of the comparative incidence of cholera among subscribers to the city’s two water companies, he showed that cholera occurred much more frequently in customers of one water company. This company drew its water from the lower Thames, which become contaminated with London sewage, whereas the other company obtained water from the upper Thames. Snow’s evidence soon gained many converts. A striking incident during this epidemic has become legendary. In one neighborhood, the intersection of Cambridge Street and Broad Street, the concentration of cholera cases was so great that the number of deaths reached over 500 in 10 days. Snow investigated the situation and concluded that the cases were clustered around the Broad Street pump. He advised an incredulous but panicked assembly of officials to have the pump handle removed, and when this was done, the epidemic was contained. Snow was a skilled practitioner as well as an epidemiologist, and his creative use of the scientific information of his time is an appropriate example for those interested in disease prevention and control. [3]