London's microbiota - John Snow in Soho
20 Jan 2020
The merest glance at the audience of a SfAM meeting and the riot of style, colour and cutting edge design on view will tell you that our members take fashion very seriously. Few, therefore, will need any introduction to Soho’s Carnaby Street, a magnet for the fashion conscious since the 1960s. While there pursuing the latest sartorial trend, many will have noticed, at the junction of Carnaby Street and Broadwick Street, a large mural in the style of Diego Rivera. The mural commemorates Soho’s huge cultural influence over the years with representations of many famous previous residents including Karl Marx, Dylan Thomas, Brendan Behan, Casanova, Mozart, Joshua Reynolds, Paul Verlaine and John Logie Baird. In the midst of these, it is possible to spot, looking rather modest and self-effacing, peeking out from behind a lady’s turban, Dr John Snow.
Originally from Yorkshire, Snow lived in Soho and its immediate environs from 1836 until his death in 1858. Much of that time he lived in nearby Frith Street, although it is with Broadwick Street that his name is particularly associated. Then called Broad Street, it has another claim to fame as the birthplace of the poet and artist William Blake, but for microbiologists everywhere it will always be linked with John Snow, the battle against cholera and the birth of epidemiology.
Snow’s investigations into cholera were not his first encounter with applied microbiology. In 1836 while studying at the Hunterian School in Great Windmill Street (also in Soho), he was encouraged by his chemistry lecturer to try a method for preserving bodies for dissection by injecting them with a solution of arsenic. In his own subsequent account in the Lancet in 1838 he records injecting the bodies with a solution of potassium arsenite and how effective it was. Regrettably though, he also had to note how one student dissecting a corpse preserved in this way fell ill with vomiting, stomach pains and diarrhoea – symptoms of arsenic poisoning - and that later, in the hot summer of 1837, similar symptoms were experienced by five of six students dissecting a similarly preserved body. Since he was one of the group of six students, he was prompted to investigate this further. His subsequent experiments established that decomposition in the bodies resulted in the conversion of the arsenic oxide to a volatile reduced form of arsenic that could be inhaled, though he was unaware that this was a microbiological process. As a result of his investigation, the use of arsenic for this purpose was discontinued.
The story of the 1854 Broad Street cholera outbreak has often been told. During an earlier outbreak in 1848 Snow had become convinced that cholera was spread by water but was unable to provide convincing evidence for this. During the Broad Street outbreak he carefully plotted cases and found that they centred on a water pump in Broad Street. Support came from the fact that workers in the Lion Brewery in Broad Street, where they drank beer, and residents of the nearby Poland Street Workhouse where they drank water from their own well, did not fall ill. Further evidence came from an apparently isolated case in distant Hampstead. Susannah Eley was a senior member of the Eley family which owned a factory in Broad Street making percussion caps for ammunition (the Eley name is still known in this context today). Having lived in Broad Street, she liked the water from the pump so much that she had some brought to her in Hampstead, with fatal results.
Armed with this accumulation of evidence, Snow and his allies decided to act. Though regarded as being a rather unconvincing public speaker, he managed to persuade the local Board of Guardians to remove the pump handle thereby isolating the primary source of the outbreak. It has been pointed out that by this time the outbreak had peaked and the number of cases was already declining rapidly but, as a dramatic gesture, it certainly adds to the story.
Snow identified cholera as being a contagious disease of the gut, spread by the faecal oral route, primarily by water, but, as with his earlier arsenic investigation, he did not recognise microorganisms as the cause. An annular, fungus-like organism associated with cholera had been described in an earlier outbreak in Bristol but this had proved to be premature. In London, the microscopist Hassall had identified large numbers of what he termed vibriones in the rice water stools from cholera victims but not in the water they consumed but thought these were a result rather than a cause of the disease. In fact, in the same year as the Broad Street outbreak, Filipo Pacini, an Italian anatomist working in Florence, published a description of the cholera bacillus and its association with disease, though this went largely unnoticed and it was not until Koch’s work published in 1884 that the matter was finally settled.
The Broad Street pump stood just outside what is now the John Snow public house (a small irony in view of the fact that Snow was an ardent teetotaller). The original has long gone although a replica pump was installed nearby to commemorate the events of 1854. At the time of writing, this too has been removed due to construction work in Broadwick Street. I did hear that a previous replica has also disappeared inexplicably. Was this the result of an over enthusiastic re-enactment by epidemiologists not content with simply removing the handle? Did it coincide with the retirement party of SfAM’s former Chief Executive in the John Snow pub? Or was it just scrap metal thieves? We’ll probably never know.
SfAM President 2011-2014