About John Snow

Portrait of John Snow

John Snow (1813–1858)

John Snow is an iconic figure in epidemiology and public health, best known for his work on cholera, for a famous map, and for organising the removal of a pump handle in Soho.

Less well known are his important contributions to anaesthesia and to epidemiological methods, and his engagement in public debates of the time. The breadth and depth of Snow’s activities provide a model for population researchers concerned not only with sound method but also with bringing their results to public benefit.

Indeed, though epidemiology is often described as the study of health-related aspects of populations, its methods are applicable to studies of virtually anything in populations, and disciplines which now acknowledge the methods and terminology of epidemiology range from education to crime science and economics.

Snow was born in York on 15 March 1813, one of eight children in a family of modest means. He apprenticed with a surgeon-apothecary in Newcastle from 1827 to 1833, and there witnessed the first epidemic of cholera in the UK.He then moved to London, qualified as physician in 1843 and set up general practice in Soho. Early in his career he became interested in the physiology of respiration in recognition of the major problem of asphyxia of the newborn.

These interests led him to be invited to witness one of the first applications of ether anaesthesia in the UK in December 1846. He immediately recognised the importance of ambient temperature and within one month published tables of the vapour pressure of ether.This initiated an important line of research on instruments for administering anaesthetics and led to his becoming the most prominent authority on anaesthesia in the UK. He administered chloroform to Queen Victoria at the birth of Prince Leopold in 1853.

The second great cholera epidemic arrived in London in 1848 and many attributed its cause to an atmospheric “effluence” or “miasma”. Snow’s firsthand experience of the disease in 1832, combined with studies of respiration, led him to question miasma theories and to publish the first edition of On the Mode of Communication of Cholera in 1849, in which he proposed that cholera was attributable to a self-replicating agent which was excreted in the cholera evacuations and inadvertently ingested, often, but not necessarily, through the medium of water.

When cholera returned in 1853, Snow recognised an ideal opportunity to test his hypothesis by comparing cholera mortality rates in populations of south London supplied by water drawn from sewage-contaminated versus uncontaminated regions of the Thames. He personally carried out a cohort study to make this comparison, recognising the need to confirm the water source of each case and to assure comparability of the populations concerned.

On 30 August 1854 while involved in these studies, a dramatic cholera epidemic began near his home in Soho leading to more than 550 deaths within two weeks. Analysis of the addresses of the cholera deaths and interviews of residents of the area led him to suspect that water from a pump on Broad Street was responsible – and he prevailed upon the local council to remove the handle of the pump on 8 September 1854.

Though the epidemic was already in decline by that date, the rapidity of his action, the logic of the analysis, and the pragmatism of the response has made this a classic event in the history of public health, well known to students and practitioners the world over. The combination of these studies provided overwhelming evidence for an infectious agent, known now as Vibrio cholerae.

Snow described this work in the second edition of On the Mode of Communication of Cholera. He then expanded his public health interests by becoming involved in debates over legislation concerning nuisance industries in London, while maintaining his research and practice in anaesthesia until his death in 1858.

The 200th anniversary of Snow’s birth provides an occasion to celebrate his achievements, to consider their original context, to discuss their place in contemporary epidemiology, and consider their likely future, not only as the armamentarium of public health, but as a framework of method for science and society.

Learn more about the work and legacy of John Snow in the School’s March podcast

Image: John Snow. Credit: LSHTM Library & Archives.