John Snow: cholera is transmitted by water (1849; Broad Street 1854; book 1855)
A proof that cholera does not spread by exhalations but enters the digestive tract with water. One of the early examples of epidemiological comparison: the same disease, the same city, different water, different mortality.
The English physician John Snow argued for waterborne transmission as early as 1849. In 1854 he matched the deaths in the London Soho against water drawn from the Broad Street pump and had the handle removed; in parallel he compared the mortality of customers of the Southwark and Vauxhall and Lambeth water companies.
The official Board of Health committee (1855) explicitly rejected his explanation in favour of an atmospheric one, and contemporaries considered his work 'ingenious but flawed'. Recognition came later, once thinking about the causes of disease had itself changed; according to Eyler, Farr's later studies contributed to it. Snow himself wrote that the incidence was already falling before the handle was removed.
Why this date
high: first pamphlet 1849; outbreak from 31 August 1854; pump handle removed 8 September 1854; second edition of the book 1855
What grew out of it
-
Koch isolates the cholera pathogen; germ theory displaces miasma
influenced · Confidence: medium
Snow's waterborne hypothesis received material confirmation when Koch isolated Vibrio cholerae; until then the cause of cholera remained a matter of debate.
Dispute: The sources record only a chronological sequence, not a direct influence of Snow on Koch: whether Koch cited Snow is not established in the available texts.
Link sources
- CDC MMWR 2004 (2004) Verified 20 Sep 2026
Despite the success of this investigation, the cause of cholera remained a matter of debate until Vibrio cholerae was isolated in 1883.
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- CDC MMWR 2004 (2004) Verified 20 Sep 2026
Other links
-
"Airs, Waters, Places": disease from air, waters and locality
refuted by · Confidence: high
Snow rejected the atmospheric (miasmatic) explanation of cholera and showed the waterborne route of transmission; contemporaries did not accept it.
Dispute: The refutation was not recognized in Snow's lifetime (he died in 1858): Halliday: "Dr John Snow's hypothesis of polluted water being a cause of cholera was not accepted in official circles at the time of his death in 1858". Eyler: "A major change in thinking about disease causation was needed before Snow's work could be widely accepted. William Farr's later studies contributed to that acceptance" (the 1866 epidemic in East London). Snow himself qualified the pump episode: "the attacks had so far diminished before the use of the water was stopped, that it is impossible to decide whether the well still contained the cholera poison in an active state". Brody et al. (Lancet 2000) show that the famous map was drawn after the investigation as an illustration, not as a tool of discovery (thesis from the abstract; no verbatim quotation extracted).
Link sources
- Snow J. 1849, p. 2 (1849)
Reasoning by analogy from what is known of other diseases, we ought not to conclude that cholera is propagated by an effluvium
- Snow J. «On the Mode of Communication of Cholera», 2nd ed., London: Churchill, 1855 (1855) Verified 20 Sep 2026
I had an interview with the Board of Guardians of St. James's parish, on the evening of Thursday, 7th September, and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day.
- Report of the Committee for Scientific Inquiries, General Board of Health 1855, p. 52, Paneth et al. 1998 (1855)
it has been suggested by Dr. Snow, that the real cause of whatever was peculiar in the case lay in the use of one particular well, situate at Broad Street...After careful inquiry, we see no reason to adopt this belief.
- Report of the Committee for Scientific Inquiries, General Board of Health 1855, p. 48, Paneth et al. 1998 (1855)
on the whole evidence, it seems impossible to doubt that the influences, which determine in mass the geographical distribution of cholera in London, belong less to the water than to the air.
- Eyler J.M. 2001, abstract (2001) Verified 20 Sep 2026
In the 1840s and 1850s Farr's work was considered definitive, while Snow's was regarded as ingenious but flawed.
- Hempel S. (2024) Verified 20 Sep 2026
Snow was derided and dismissed
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Snow J. 1849, p. 2 (1849)
Node sources
- Snow J. On the Mode of Communication of Cholera, 2nd ed. (1855) (1855) Verified 20 Sep 2026
the so-called outbreak, which commenced in the night between the 31st August and the 1st September, was, as in all similar instances, only a violent increase of the malady.
- Snow J. On the Mode of Communication of Cholera, 2nd ed. (1855) (1855) Verified 20 Sep 2026
there is no doubt that the mortality was much diminished, as I said before, by the flight of the population, which commenced soon after the outbreak; but the attacks had so far diminished before the use of the water was stopped, that it is impossible to decide whether the well still contained the cholera poison in an active state, or whether, from some cause, the water had become free from it.
- Cholera Inquiry Committee, Report (1855), Paneth N. et al. «A rivalry of foulness», Am. J. Public Health 88(10) (1998)
In explanation of the remarkable intensity of this outbreak within very definite limits, it has been suggested by Dr. Snow, that the real cause... lay in the use of one particular well... After careful inquiry, we see no reason to adopt this belief.
- Eyler J. M. «The changing assessments of John Snow's and William Farr's cholera studies», Sozial- und Präventivmedizin 46, 225-232 (2001) Verified 20 Sep 2026
In the 1840s and 1850s Farr's work was considered definitive, while Snow's was regarded as ingenious but flawed.
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
Further reading
Not evidence: these carry no quotation and support nothing we wrote. They are books and scans to read next.
- Snow J. On the Mode of Communication of Cholera (1849), John Snow Archive (MSU) (1849)
- Paneth N. et al. A rivalry of foulness: official and unofficial investigations of the London cholera epidemic of 1854. Am. J. Public Health 88(10): 1545-1553 (1998)
- Brody H., Rip M.R., Vinten-Johansen P., Paneth N., Rachman S. Map-making and myth-making in Broad Street: the London cholera epidemic, 1854. Lancet 356(9223): 64-68 (2000)