John Snow was a London physician and anaesthetist who is now regarded as one of the pioneers of modern epidemiology. He was particularly interested in how diseases spread, and during the cholera epidemics of the 1840s and 1850s he challenged the dominant idea that cholera was caused by miasma, basically poisonous or disease carrying air. Snow argued instead that cholera was being spread by contaminated water.
During the 1854 cholera outbreak in Soho, Snow mapped the deaths in the area and noticed that they were heavily concentrated around the Broad Street water pump. He investigated the water supply, compared it with other sources, and persuaded the local authorities to remove the pump handle. The outbreak was already declining, so removing the handle did not magically end the epidemic, but Snow’s investigation provided an important piece of evidence for his argument.
Snow’s theory was not immediately accepted. The Committee for Scientific Inquiries rejected his explanation in 1855, stating that they saw no reason to accept his belief that cholera had been spread by contaminated water from the Broad Street well. The prevailing view continued to give a major role to miasma and contaminated air.
Meanwhile, investigation of the Broad Street site found that a cesspool at 40 Broad Street was only about 2 ft 8 in from the well, with defective brickwork allowing contamination to reach the well. Snow later described the separation as roughly three feet. The exact timing and evidence are more complicated than the meme makes them look, but the basic joke is very much rooted in the historical record.
Snow died in 1858, before his theory was widely accepted. The 1866 cholera outbreak in London provided much stronger evidence for the waterborne theory, and William Farr, who had previously favoured other explanations, eventually accepted the importance of contaminated water. Snow’s methods, particularly using maps, mortality data and comparisons between different water supplies to investigate disease transmission, are now regarded as foundational to the development of field based epidemiology.
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