John Snow’s “Grand Experiment,” 1855

As London suffered one of its worst cholera outbreaks, in the summer of 1853, John Snow took it upon himself to prove that the disease was transmitted through drinking water.

Daniel Grushkin
Jul 31, 2010


For 14 weeks in the late summer of 1853, London suffered one of its worst cholera outbreaks. The leading voices in medicine believed the disease emanated from the foul gasses of London’s polluted streets. John Snow, a prominent anesthesiologist, was convinced otherwise. “He was the original intellectual maverick,” says Ralph Frerichs, professor emeritus of epidemiology at the UCLA School of Public Health. With this map of South London, Snow believed he could prove that cholera was transmitted through drinking water. But while he would later become known as the father of modern epidemiology, his peers of the time rejected his theory. Now, some contemporary medical historians are agreeing that Snow may not have had an ironclad case.

Map courtesy of The John Snow Site (
#1 - The colors represent the territories of two companies that piped drinking water to South London. The Lambeth Company (red) drew...