John Snow (physician)

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John Snow (1813-1858), was a British physician who is considered to be one of the founders of epidemiology for his work identifying the source of a cholera outbreak in London in 1854. He was also one of the pioneers of anaesthesia and medical hygiene. He experimented with ether as an anaesthetic, and designed apparatus to administer it safely. When the anaesthetic effects of chloroform were reported, he swiftly adopted it in preference to ether, and designed a mask to administer it. In 1853 and 1857, he personally administered chloroform to Queen Victoria during the births of her eighth and ninth children; this royal endorsement was instrumental in ensuring the rapid acceptance of chloroform as an anaesthetic in obstetrics.

While a British poll in 2003 may have been a bit weighted, he was voted the greatest physician of all time — yet he is relatively unknown outside medical circles.[1]

Early life

John Snow was born on March 16, 1813 in York, England; he was the first of nine children born to William and Frances Snow in their North Street home. He studied in York until the age of 14, when he was apprenticed to William Hardcastle, a surgeon in Newcastle-upon-Tyne. In October 1836 he enrolled as a student at the Hunterian school of medicine in Great Windmill Street, London. A year later, he began working at the Westminster Hospital and was admitted a member of the Royal College of Surgeons of England on May 2, 1838. He graduated from the University of London in December 1844, and was admitted to the Royal College of Physicians in 1850.

Contributions to Epidemiology

"In Manchester, a sudden and violent outbreak of cholera occurred in Hope Street, Salford. The inhabitants used water from a particular pump well. This well had been repaired, and a sewer which passes within nine inches of the edge of it became accidentally stopped up, and leaked into the well. The inhabitants of thirty houses used the water from this well; among them there occurred nineteen cases of diarrhea, twenty-six cases of cholera, and twenty-five deaths. The inhabitants of sixty houses in the same immediate neighborhood used other water; among these there occurred eleven cases of diarrhea, but not a single case of cholera, nor one death. It is remarkable, that, in this instance, out of the twenty-six persons attacked with cholera, the whole perished except one."[2]

John Snow's first piece of scientific research was on the use of arsenic for preserving bodies. He abandoned these studies because of the toxic effects on the medical students. On 16 October 1841, John Snow presented his first paper entitled "Asphyxia and the resuscitation of new-born children." His studies in toxicology led him to an interest in cholera, and in particular to his theory on the transmission of the cholera 'poison' in water supplies. In 1849, he published the first edition of On the mode of communication of cholera. It was not well received at first ("There is, in our view, an entire failure of proof that the occurrence of any one case could be clearly and unambiguously assigned to water" according to one contemporary reviewer[3]), but this work is now regarded as an important milestone in the history of epidemiology. In it, he first set out the case that cholera was a disease communicated from person to person. He then argued that it was not communicated by means of airborne effluvia; he noted that merely being close to a patient was not sufficient to catch the disease, yet the disease spread to others in the neighbourhood who had not been in direct contact with a victim. He further argued that, if the lungs were the site of primary infection, the lungs should be expected to be the origin of the initial symptoms. Instead, from his own observations and those of others, he concluded that cholera always first affects the alimentary canal. From this he deduced that the disease arose from the accidental swallowing of minute quantities of a material (with, he speculated, a cell-like structure) which then reproduced itself inside the stomach and bowels.

He concluded that the faeces of an affected person would thus contain the infective material, and that this might then be spread to others through contamination of drinking water. By carefully recording the location of deaths related to cholera, he showed that in several cases, they clustered around particular shared sources of drinking water.

He argued that the crowded living conditions of the poor, and the lack of adequate sanitation, contributed to the regular outbreaks of cholera in 19th century England. In particular, he blamed the lack of facilities for handwashing on outbreaks amongst miners - who suffered disproportionately more outbreaks of cholera than any other occupation.

Snow was proposing a means of disease transmission that clearly contradicted the prevailing miasma theory. Although overlooked at the time, his study would later be recognised as evidence for the germ theory of disease, which would come to prominence in the years after Snow’s death.


John Snow explicitly rejected the contemporary theory of miasmas (i.e., "spirit-like entities that accounted for the epidemic nature of diseases like cholera"), through use of statistical analysis and evidence-based decisionmaking.

Snow felt that the miasma theory could not explain the spread of certain diseases, including cholera. During the outbreak of 1831, he had noticed that many miners were struck with the disease while working deep underground, where there were no sewers or swamps. It seemed most likely to Snow that the cholera had been spread by invisible germs on the hands of the miners, who had no water for hand-washing when they were underground...As more cases appeared, Snow began examining sick patients. All of them reported that their first symptoms had been digestive problems. Snow reasoned that this proved that the disease must be ingested with polluted food or water. If the victims had absorbed cholera poison from polluted air, as the "miasma" theorists believed, then their first symptoms should have appeared in their noses or lungs -- not in their digestive tracts. [4]

Later, he was given the honor in elaborating at the formal Oration at the Medical Society of London:

There is one class of diseases -- intermittent fevers -- which are so fixed to particular places that they have deservedly obtained the name of endemics. They spread occasionally, however, much beyond their ordinary localities, and become epidemic. Intermittent fevers are Undoubtedly often connected with a marshy state of the soil; for draining the land frequently causes their disappearance. They sometimes, however, exist as endemics, where there is no marshy land or stagnant water within scores of miles. Towards the end of the seventeenth century, intermittent fevers were, for the first time, attributed by Lancisi to noxious effluvia arising from marshes. These supposed effluvia, or marsh miasmata, as they were afterwards called, were thought to arise from decomposing vegetable and animal matter; but, as intermittent fevers have prevailed in many places where there was no decomposing vegetable or animal matter, this opinion has been given up in a great measure; still the belief in miasmata or malaria of some kind, as a cause of intermittents, is very general. It must be acknowledged, however, that there is no direct proof of the existence of malaria or miasmata, much less of their nature. Intermittent fevers were attributed to such agents from the absence of any other known cause, especially as they were observed to come on after exposure to the air of Certain localities, more particularly at night.[5]

Action as well as words

His best-known achievement was the early use of statistical methodology to track the source of cholera outbreaks in London. When the relevant authorities considered, he took direct action and cut the handle off the Broad Street Pump, stopping the epidemic at the source. The details are available in the page on Epidemiology#History.

His classic work ends with far-sighted practical recommendations for the prevention of cholera and other diseases, including typhoid fever, dysentery and plague, which Snow argued had a similar mode of communication. Those recommedations included an emphasis on cleanliness - "There should be a hand-basin, water, and towel, in every room where there is a cholera patient, and care should be taken that they are frequently used by the nurse and other attendants, more particularly before touching any food." He argued that the soiled bed linen and clothes of the patient should be immersed in water as soon as they are removed, until they can be washed, lest the evacuations should become dry, and be wafted about as a fine dust. He argued that it was essential that all water used for drinking and preparing food was uncontaminated, and if there was any dount, it should be well boiled, and, if possible, also filtered.

Contributions to Anaesthesia

Snow was one of the first physicians to study and calculate dosages for the use of ether and chloroform as surgical anaesthesia. 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.[6] This led to wider public acceptance of obstetric anaesthesia. Snow published an article on ether in 1847 entitled "On the Inhalation of the Vapor of Ether". A longer work was published posthumously in 1858 entitled "On Chloroform and Other Anaesthetics, and Their Action and Administration"

Other facts

He was an early proponent of the Germ theory of disease. Perhaps the earliest documented application of Geographic Information System has been by him.

Remembering John Snow


  1. Department of Epidemiology, School of Public Health, University of California at Los Angeles, John Snow Site
  2. On the mode of communication of cholera,by John Snow, M.D. London: John Churchill, New Burlington Street, England, 1855
  3. (London Medical Gazette, 1849)[1]
  4. David Vachon, Doctor John Snow Blames Water Pollution for Cholera Epidemic, Department of Epidemiology, School of Public Health, University of California at Los Angeles
  5. John Snow (1853), Oration 2, On Continuous Molecular Changes, More Particular in Their Relation to Epidemic Diseases: Being the Oration Delivered at the 80th Anniversary of The Medical Society of London., John Churchill
  6. Anesthesia and Queen Victoria (HTTP). John Snow. Department of Epidemiology UCLA School of Public Health. Retrieved on 2007-08-31.