Body & HealthFact
A map and a pump handle defeated cholera.
In 1854 more than 600 Londoners died of cholera within days. John Snow plotted every death on a map – they clustered around the Broad Street water pump. He had the handle removed; the outbreak was already fading, but the map was convincing. That a bacterium was the cause wasn't accepted until decades later.
Useful: Finding patterns in data is where all epidemiology starts.
Source: en.wikipedia.org