John Snow (physician)

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 1854. He was also one of the pioneers of anaesthesia and medical hygiene. 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.

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

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, but his studies in toxicology led him to an interest in cholera, and led to his theory on the transmission of the cholera 'poison' in water supplies.

Miasmas

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.

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.

Action as well as words

"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."

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.

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. 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

• The John Snow Society [1] aims to promote his life and works.
• Durham University [2] has opened a college to commemorate his contributions [3].
• The John Snow Archive and Research Companion [4] is hosted by the Department of Epidemiology at Michigan State University.
• The CDC has a page dedicated to him [5].