• Physician John Snow, 1813
  

In 1837, Snow began working at the Westminster Hospital, admitted as a member of the Royal College of Surgeons of England on 2 May 1838, he graduated from the University of London in December 1844 and was admitted to the Royal College of Physicians in 1850.

In 1857, he made an early and overlooked contribution to epidemiology in a little known pamphlet: On the adulteration of bread as a cause of rickets.

John Snow was one of the first physicians to study and calculate dosages for the use of ether and chloroform as surgical anesthetics, allowing patients to undergo surgical procedures without the distress and pain they would otherwise experience. He personally administered chloroform to Queen Victoria when she gave birth to the last two of her nine children, Leopold in 1853 and Beatrice in 1857, leading to wider public acceptance of obstetric anesthesia. Snow published an article on ether in 1847 entitled On the Inhalation of the Vapor of Ether. A bigger, longer work was published posthumously in 1858 entitled On Chloroform and Other Anaesthetics, and Their Action and Administration.

Snow was a skeptic of the then dominant miasma theory that stated that diseases such as cholera or the Black Death were caused by pollution or a noxious form of "bad air". The germ theory of disease had not yet been developed, so Snow did not understand the mechanism by which the disease was transmitted. His observation of the evidence led him to discount the theory of foul air. He first publicized his theory in an essay On the Mode of Communication of Cholera in 1849. Despite continuing reports, he was awarded 30,000 French francs for this work by the Institut de France. In 1855 he published a second edition of his article, documenting his more elaborate investigation of the effect of the water supply in the Soho, London epidemic of 1854.

By talking to local residents (with the help of Reverend Henry Whitehead), he identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street). Although Snow's chemical and microscope examination of a water sample from the Broad Street pump did not conclusively prove its danger, his studies of the pattern of the disease were convincing enough to persuade the local council to disable the well pump by removing its handle. This action has been commonly credited as ending the outbreak, but Snow observed that the epidemic may have already been in rapid decline:

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.

Snow later used a dot map to illustrate the cluster of cholera cases around the pump. He also used statistics to illustrate the connection between the quality of the water source and cholera cases. He showed that the Southwark and Vauxhall Waterworks Company was taking water from sewage - polluted sections of the Thames and delivering the water to homes, leading to an increased incidence of cholera. Snow's study was a major event in the history of public health and geography. It is regarded as the founding event of the science of epidemiology.

Snow wrote:

On proceeding to the spot, I found that nearly all the deaths had taken place within a short distance of the [Broad Street] pump. There were only ten deaths in houses situated decidedly nearer to another street pump. In five of these cases the families of the deceased persons informed me that they always sent to the pump in Broad Street, as they preferred the water to that of the pumps which were nearer. In three other cases, the deceased were children who went to school near the pump in Broad Street...

With regard to the deaths occurring in the locality belonging to the pump, there were 61 instances in which I was informed that the deceased persons used to drink the pump water from Broad Street, either constantly or occasionally...

The result of the inquiry, then, is, that there has been no particular outbreak or prevalence of cholera in this part of London except among the persons who were in the habit of drinking the water of the above mentioned pump well.

I had an interview with the Board of Guardians of St James's parish, on the evening of the 7th inst [Sept 7], and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day.

—John Snow, letter to the editor of the Medical Times and Gazette

Later, researchers discovered that this public well had been dug only three feet from an old cesspit, which had begun to leak fecal bacteria. The nappies of a baby, who had contracted cholera from another source, had been washed into this cesspit. Its opening was originally under a nearby house, which had been rebuilt farther away after a fire. The city had widened the street and the cesspit was lost. It was common at the time to have a cesspit under most homes. Most families tried to have their raw sewage collected and dumped in the Thames to prevent their cesspit from filling faster than the sewage could decompose into the soil.

After the cholera epidemic had subsided, government officials replaced the Broad Street Pump Handle. They had responded only to the urgent threat posed to the population, and afterward they rejected Snow's theory. To accept his proposal would have meant indirectly accepting the oral - fecal method transmission of disease, which was too unpleasant for most of the public to contemplate.

Public health officials recognize the political struggles in which reformers have often become entangled. During the Annual Pumphandle Lecture in England, members of the John Snow Society remove and replace a pump handle to symbolize the continuing challenges for advances in public health.

In 1830 Snow became a member of the Temperance Movement, and lived for a decade or so as a vegetarian and teetotaler. In the mid 1840s his health deteriorated, and he returned to meat eating and drinking wine. He continued drinking pure water (via boiling) throughout his adult life. He never married.

At the age of 45, Snow suffered a stroke while working in his London office on 10 June 1858. He never recovered, dying on 16 June 1858 and is buried in Brompton Cemetery.

• A plaque commemorates Snow and his 1854 study in the place of the water pump on Broad Street (now Broadwick Street). It shows a water pump with its handle removed. The spot where the pump stood is covered with red granite.
• A public house nearby was named "The John Snow" in his honor.
• His grave in Brompton Cemetery, London, is marked by a funerary monument.
• In York, a blue plaque commemorates Snow on the west end of the Park Inn, a hotel in North Street.
• Snow was named as one of the heraldic supporters of the Royal College of Anaesthetists.
• 2003, a poll of British doctors ranked Snow as the greatest physician of all time.
• 2001, John Snow College, founded on the University of Durham's Queen's Campus in Stockton - on - Tees, was named in his honor.