John Snow & What He Did Know

Standing outside the John Snow pub in Soho on a Saturday afternoon, I heard two separate references to the broody Game of Thrones character in the space of 5 minutes. But this pub isn’t named for the fictional icon who was famously teased “you know nothing, Jon Snow.” Instead, it commemorates a man who is celebrated for what he did know, for what he discovered. In his lifetime [1813 – 1858], the pub’s namesake was a highly-regarded anesthesiologist, physician to the  Queen herself. Beyond his qualifications as a physician, Snow is known as ‘the father of epidemiology’ because he was creative, imaginative and observant enough to realize that death-delivering cholera is borne, not by air, but by water.


John Snow vilified the Broad Street water pump when he called for its handle to be removed on the assertion that it was spreading cholera. This was 1854, before we knew that cholera was caused by a waterborne bacterium, the infamous Vibrio cholerae. This was before the first images of bacteria were captured, before we knew that bacteria thrive almost everywhere on Earth. This was before anybody knew anything about bacteria at all. In Snow’s time, it was widely believed that cholera and many other diseases were transmitted by foul air. This ‘miasma theory’ was used to justify much of public health decision-making in Europe, India and China until the late 19th century. So if nobody knew that bacteria existed, how did Snow realise, seemingly against common sense, that the pump was a villain? He invented a new investigative approach that kick-started the medical field of epidemiology, he created a new kind of map that geographers still toast today, and he had help from a local priest named Henry Whitehead.

If you go looking for the Broad Street pump you will find a dirty pink commemorative kerbstone. Barely distinguishable from the surrounding grey, it’s an easily missed hat-tip to the Broad Street villain of old. I stood on that pink granite trying to think myself back in time, to imagine what that place was like when John Snow was walking around. How did I end up there, looking up at the apartment windows imagining 19th century families dying of cholera inside? I thank Steven Johnson and his book, The Ghost Map [2006]for that.

the ghost map

With affectionately described characters, welcome illustrations and plentiful Dickens quotations, The Ghost Map delivers an entertaining account of ground-breaking research. Johnson recounts the investigations of John Snow and Henry Whitehead, illuminating the key attributes that enabled their work – tenacity, fearlessness, humility and commitment to truth uncompromised by self-interest. Johnson shows how the success of their investigations depended on giving rational observations precedence over assumption and prejudice. Snow and Whitehead were willing “to challenge orthodoxy.” They recognized “aberrations, deviations from the norm” as opportunities for understanding and relied on data to examine patterns rather than adopting the common belief in a “moral component to illness.” Both Snow and Whitehead were local to the Broad Street area and they relied heavily on intimate knowledge of the neighbourhood and its occupants.

Johnson shows how a misleading paradigm of thought (miasma theory) was overcome by working across different disciplines and at various scales. In a way, Snow and Whitehead were able to see something invisible – they were able to show that something in the water was causing cholera before they knew what it was. They pointed a finger at the enemy without ever seeing it. Even Sherlock Holmes would applaud.

No doubt, Snow’s work was brilliant: it helped build a foundation for the germ theory of disease and birthed a whole new ‘-ology’. But was it responsible for the great clean-up of London, the so-called sanitary revolution? In discussing sanitary reform, The Ghost Map focuses almost exclusively on scientific understanding and gives scant consideration to critical aspects like political will, governance, or corruption. Johnson writes that “after years of bureaucratic waffling, the Great Stink finally motivated the authorities to deal with…the contamination of the Thames”. With little more said on the matter, the book neglects the political, economic and societal forces that were responsible, far more than ignorance or the miasma theory, for the sanitary conditions in 19th century London.

The Ghost Map presents the miasma theory as a significant hindrance to improving water infrastructure in London. However, perhaps missing the contradiction, it also acknowledges that Snow’s waterborne theory of cholera was only widely accepted after an elaborate, world-renowned sewerage system was built in London. Long before science provided an explanation, “societies throughout time were cognizant of the linkage between water and illness”[Solomon 2010, 252]. That was reason enough for Scotland and northern British industrial towns to construct extensive waterworks by 1850 to combat shortages and provide cleaner water. Even in London, a filtration system was introduced for Chelsea in 1828. Belief in miasma and in the importance of clean water were not mutually exclusive.

After the first cholera outbreak in England, a commentator in a medical journal stated that ‘there was never a real panic’ because it was quickly realised that the great majority of cholera victims were among ‘the poorest of the poor’ [Inglis 1971, 272]. So the sanitary crisis was a reflection of social inequality, it was also “an early manifestation of an inherent dilemma in the industrial market economy”: the lack of an internal mechanism to ensure environmental sustainability [Solomon 2010, 260]. Furthermore, there was ongoing debate over the rightful role of London’s government as the administrative class and industrial magnates had risen to prominence, heralding a shift from self-serving aristocratic ideals towards Victorian ideals of “social conscience and civic pride” [Plumb 1963, 84-87]. By not including such context, The Ghost Map overstates the importance of miasma theory and the Broad Street case.

Nevertheless, it tells an interesting and important story. It’s a memorable read that engages the reader from start to finish and I very much enjoyed it. Don’t turn to it to understand the sanitary revolution, it provides an incomplete story in that regard. Turn to it for a story of human ingenuity. I recommend it for anyone who likes history, is interested in water quality and disease, thinks about scientific progress, or simply wants to read a well-told story about an unusual man with an unchained mind.

Inglis, B. (1971). Poverty and the Industrial Revolution, London: Hodder and Stoughton Limited

Plumb, J. H. (1963). England in the Eighteenth Century, London: Penguin Group

Solomon, S. (2010) Water: The Epic Struggle for Wealth, Power, and Civilization, New York: HarperCollins Publishers.