John Snow (15 March 1813 – 16 June 1858[1]) was an English physician and a leader in the development of anaesthesia and medical hygiene.

He is considered one of the founders of modern epidemiology and early germ theory, in part because of his work in tracing the source of a cholera outbreak in London's Soho, which he identified as a particular public water pump.

His father was a labourer[3] who worked at a local coal yard, by the Ouse, constantly replenished from the Yorkshire coalfield by barges, but later was a farmer in a small village to the north of York.

[5] Between 1832 and 1835 Snow worked as an assistant to a colliery surgeon, first in Burnopfield, County Durham, and then in Pateley Bridge, West Riding of Yorkshire.

In 1841, he wrote, On Asphyxiation, and on the Resuscitation of Still-Born Children, which is an article that discusses his discoveries on the physiology of neonatal respiration, oxygen consumption and the effects of body temperature change.

[15] In 1857, Snow made an early and often overlooked[16] contribution to epidemiology in a pamphlet, On the adulteration of bread as a cause of rickets.

[5] As well as ether, John Snow studied chloroform, which was introduced in 1847 by James Young Simpson, a Scottish obstetrician.

Snow first realised this with Hannah Greener, a 15-year-old patient who died on 28 January 1848 after a surgical procedure that required the cutting of her toenail.

However, on 7 April 1853, Queen Victoria asked John Snow to administer chloroform during the delivery of her eighth child, Leopold.

[5] Snow was a skeptic of the then-dominant miasma theory that stated that diseases such as cholera and bubonic plague were caused by pollution or a noxious form of "bad air".

He first published his theory in an 1849 essay, On the Mode of Communication of Cholera,[22] followed by a more detailed treatise in 1855 incorporating the results of his investigation of the role of the water supply in the Soho epidemic of 1854.

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.

He showed that homes supplied by the Southwark and Vauxhall Waterworks Company, which was taking water from sewage-polluted sections of the Thames, had a cholera rate fourteen times that of those supplied by Lambeth Waterworks Company, which obtained water from the upriver, cleaner Seething Wells.

[citation needed] 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.

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 [7 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.Researchers later discovered that this public well had been dug only 3 feet (0.9 m) from an old cesspit, which had begun to leak faecal bacteria.

[30] It was not until 1866 that William Farr, one of Snow's chief opponents, realised the validity of his diagnosis when investigating another outbreak of cholera at Bromley by Bow and issued immediate orders that unboiled water was not to be drunk.

[33] During the annual Pumphandle Lecture in England, members of the John Snow Society remove and replace a pump handle to symbolise the continuing challenges for advances in public health.

[35] His health deteriorated and he suffered a renal disorder which he attributed to his vegan diet so he took up meat-eating and drinking wine.

[39] It has been speculated that his premature death may have been related to his frequent exposure and experimentation with anesthetic gases, which is now known to have numerous adverse health effects.