Snow lived at a time when there was a fierce debate underway about whether cholera (and many other diseases) were caused by dirty air (or “miasmas”), dirty water, or other means of transmission. This was also a time when science was in full flower and advances in human understanding were racing ahead. In 1849, Snow published a treatise “On the Mode of Communication of Cholera,” which argued that it was caused by exposure to contaminated water. That book also cited case studies of the transmission of cholera in polluted waters from Rotherhithe, Manchester, Ilford, Bath, Newburn on the Tyne, and through the Black Sea Fleet. The local medical establishment was not convinced:
“Notwithstanding our opinion that Dr Snow has failed in proving that cholera is communicated in the mode in which he supposes it to be, he deserves the thanks of the profession for endeavouring to solve the mystery. It is only by close analysis of facts and the publication of new views, that we can hope to arrive at the truth”. (London Medical Gazette, 1849)
Snow continued his work on the issue. A breakthrough occurred in the mid-1850s when another in a series of severe cholera outbreaks hit London. He is best remembered today for his work in 1854, when he created a now famous map to show the link between cholera cases and water sources.
I recently wrote a book about the story of bottled water, which includes a discussion of the history of cholera, water treatment, and John Snow. In that book, I described Snow’s experience as follows:
“In the 1850s, the river smelled so bad on hot summer days that Parliament would adjourn because of the stink. Health officials in England had observed that cholera and typhoid mortality were five to six times higher in the poorer districts getting water from the sewage-contaminated Lower Thames compared to wealthier West London, which received cleaner water from upstream. In 1848, the Lambeth Water Company, one of several private water companies supplying London moved its water intake upstream on the Thames, above the worst of the sewage discharges, reducing illness in its service area.
In a now legendary experiment in 1854, Dr. John Snow, a London physician, conducted a simple yet brilliant test that helped to settle the debate about the transmission of cholera. Snow drew a map [see Figure 2 below] of a virulent cholera outbreak in one of the poorest neighborhoods of London – served by central wells and no sewage collection. He plotted the homes and numbers of people affected, and in a flash of insight, mapped the location of the wells that provided water for the hardest hit neighborhoods. The maps he generated and the interviews he conducted with the families of victims convinced him that the source of contamination was the water from the Broad Street well. He received permission from local authorities to remove the pump, which forced residents to go to other, uncontaminated wells for water. Within days, the outbreak subsided.” [from “Bottled and Sold: The Story Behind Our Obsession with Bottled Water” Island Press, Washington DC.]
This is John Snow’s famous map. On it, I’ve colored in red his column of bars, each of which represents a cholera death. I’ve also circled in blue the local water pumps, including the Broad Street pump — servicing the well that was the source of cholera.