Early epidemiology
Original map by John Snow showing the clusters of cholera cases in the London epidemic of 1854. John Snow's investigative work was one of the first examples of epidemiology. He discovered that families that drew their water from the Broad St well became infected with cholera.
Source
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"London epidemic of 1854."
http://en.wikipedia.org/wiki/Epidemiology%23mediaviewer/File:Snow-cholera-map.jpg
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