At the other conference I attended last week (which I thankfully finished transcribing my notes from yesterday) we spent two days discussing the kinetics and mode of action of perfluorinated compounds (a class of chemicals used to make non-stick surfaces and flame-retardant materials that have the disturbingly long half-life of 4 years in a human). An epidemiologist from one of the two companies involved in the manufacture of the chemicals related the following anecdote which may be familiar to those more medically/biologically inclined but was new to me.
In 1854, Dr. John Snow managed to suppress an outbreak of cholera in the Soho district of London by simply marking the locations of water pumps on a map and then marking the location of cholera cases. Most of the cases clustered around a single water pump, so he removed the handle. The outbreak subsided and, to this day, the water pump handle is a major symbol for epidemiology.
Wikipedia actually had a copy of the map used by Snow: