'Nobody is healthy in London, nobody can be'
As it is usually told, the story of John Snow and cholera begins with one of those great moments that historians used to be so fond of. On the morning of 8th September 1854 a party of workmen removed the handle of a public water-pump, on what was then Broad Street in Soho. They were acting on the advice of Snow – a general practitioner and anaesthetist with rooms a few streets away. At an emergency meeting the previous evening, he had convinced the parish authorities that water from this pump was responsible for a terrible cholera outbreak, which had killed more than five hundred people in less than two weeks.
Since the 1930s many writers have woven a heroic myth around the story of the Broad Street pump. They have argued that Snow discovered the cause of cholera (which, as he himself made clear, he did not); that he saved many lives by disabling the pump (which, as we shall see, is moot); and that he revolutionised the way in which politicians, physicians and public health reformers thought about cholera (which, again, he did not).
Ever since his reappearance as a founding father of epidemiology and public health, Snow and his work on cholera have been both troublesome and enormously useful for historians of medicine like me. Studies of Snow have complicated and enriched our understanding of nineteenth-century British history, taking us to the places where medicine collided with science, politics and culture. But how should we understand his life and his ideas? – ideas that should, it seems to many modern observers, have been far more influential than they actually were.
In this essay I want to introduce you to the John Snow revealed by a generation of medical historians. He is a man, not a marble statue, neither before nor ahead of his time (whatever that might mean), but clearly and intriguingly of it. Snow lived in an age of revolutions, in a time of startling new knowledge and radical uncertainties. His work becomes more fascinating and more impressive, not less, when seen in its historical context. And it is far more than a crude, polarised struggle between his own genius and his contemporaries’ stupidity. Snow was courageous and clear-sighted, but most of all human – lucky in many ways, and in some larger ways unlucky. This is a story shot through with illuminating paradoxes, and it begins not with a pump-handle in Soho, but a deathbed in Northumbria.
(Two caveats. This essay was written as a public lecture, to be presented at the John Snow bicentenary conference in York on 15th March 2013. I have added a bibliography of sources at the end, and will gladly supply detailed references on request. And it is not a piece of original research, but (I hope) a readable re-retelling of the story of John Snow and cholera, written from the perspective of current historiographical thinking. Most of the arguments are drawn with gratitude from the excellent secondary literature on this subject, with particular thanks to Christopher Hamlin and Stephanie Snow. If you’d prefer to listen rather than read, try this podcast from The Naked Scientists, or this episode of the Nature Podcast, in which I give a potted history of Snow’s life and work.)
At noon on Wednesday 26th October 1831 a keelman named William Sproat died in his lodgings in the busy port of Sunderland. Sproat’s decline had been frighteningly swift. On the previous Saturday he had dined on a mutton chop (against the advice of his doctor) and afterwards strolled down to the riverside. On his return he was struck with a fever, stomach cramps, and – most ominously – uncontrollable explosive diarrhoea. The next morning a local surgeon, Mr Holmes, recorded his impressions of Sproat’s condition:
Evidently sinking; pulse almost imperceptible, and extremities cold, skin dry, eyes sunk, lips blue, features shrunk, he spoke in whispers, violent vomiting and purging, cramps of the calves and legs, and complete prostration of strength.
Later that day another surgeon – JB Kell of the 82nd Regiment of Foot, stationed in Sunderland – came to call. Kell had witnessed an outbreak of ‘Asiatic cholera’ while stationed in Mauritius, and he recognised the symptoms he saw. Sproat was treated with brandy, opium and calomel – mercury chloride – but he continued to sink. On Wednesday morning Holmes found his patient with ‘Pulse scarcely beating under the fingers, countenance quite shrunken, lips dark blue’, and by midday he was dead. Looking back, doctors spotted earlier cases of ‘Asiatic cholera’ in Sunderland, but Sproat was the first confirmed death from this disease in these isles.
However – our first paradox – cholera was in an important sense not at all new. British doctors had been diagnosing their patients with cholera for centuries before 1831. To see why, we need to look at the ancient roots of Western medicine. In Classical thought, health and disease were determined by the ebb and flow of four humours: blood, phlegm, black bile and yellow bile. Those whose bodies were dominated by hot, dry yellow bile – choler – had a choleric temperament, hot-tempered and easily angered. Yellow bile was the predominant humour of summer, adulthood and hot climates, and so was only to be expected at the end of a long summer, or amongst hot-blooded soldiers on an island like Mauritius. In this sense, ‘a cholera’ was not necessarily a disease. It might be a kind of natural purging, the body ridding itself of excess yellow bile as the seasons turned, or as one passed from adulthood into older age. Only when this purging became excessive was it considered pathological, and given a name – cholera morbus, literally ‘bile sickness’.
This humoral understanding broadened somewhat in the eighteenth century, as medicine took a post-Cartesian, post-Newtonian interest in the body as a machine, whether nervous, electrical, hydraulic or mechanical. And from the early nineteenth century European doctors began to move away from a view of disease as a general constitutional imbalance and towards a new focus on specific causes and localised lesions in organs and tissues. But when ‘Asiatic cholera’ began to move west from Bengal in 1817, it was seen at first to be a new and much more severe version of a known condition, one to which victims might be predisposed by their environment, lifestyle and constitution. The great transformation in attitudes towards the disease began with the first European epidemic of 1831-32. It is difficult to exaggerate the fear provoked by cholera’s seemingly inexorable movement across continents and oceans towards Britain. An editorial in the Quarterly Review called it:
[O]ne of the most terrible pestilences which have ever devastated the earth … If this malady should really take root and spread in these islands, it is impossible to calculate the horror even of its probable financial results alone.
How typical of the High Tory Quarterly – ‘so savage and Tartarly’, in Byron’s words – to think first of money. But here, again, we encounter a paradox. In Victorian politics and culture, cholera was enormously significant. As we shall see, it provoked a revolution in public health, political ideology and the treatment of the poor. It became a running theme in the Times, the Lancet, the novels of Charles Dickens, and the scribblings of many less distinguished hacks and pamphleteers. And it gave its name to an age: historians still refer to the middle third of the nineteenth century as ‘the cholera years’.
Demographically, however, cholera’s impact was less clear-cut. It was epidemic, not endemic like tuberculosis, and Britain suffered four short epidemics over four decades (1831-2, 1848-9, 1853-4, and 1866). Compare this with the Black Death, which returned dozens of times over three centuries, and in its first visitation carried off perhaps a third of Europe’s population. Over the nineteenth century cholera killed far fewer people than tuberculosis or the diseases of childhood. Even at the height of the 1831-32 epidemic, cholera was never more than the third most common cause of death, after consumption and convulsions. So how can we explain the peculiar fear and horror of ‘Asiatic cholera’?
First, think of the name. ‘Asiatic’ or ‘Indian cholera’ reflected the perceived origin of the disease in Bengal, but it also expressed disquiet about the underside of British imperialism. For Britain, the nineteenth century was an age of endless movement, of wars, migrations, exploration and trade. One distinctively Victorian vision of utopia was built on the free movement of people, commodities and capital. For a time, it seemed impossible to have this without a free trade in diseases like cholera. The old, gentle, seasonal cholera became known as cholera nostra, ‘our cholera’; the new ‘Asiatic cholera’ was, so to speak, ‘their cholera’ – a disease of filthy, uncivilised savages, whether they dwelt in the slums of Soho or the bustees of Calcutta, which threatened to overwhelm the civilised heart of imperial government.
And when ‘Asiatic cholera’ did come, it came swiftly and without mercy. Epidemics were intense and seemingly indiscriminate, killing the fit and the strong with the young, the aged and the weak. Victorian culture was peculiarly obsessed with the idea of a ‘good death’, slow, dignified and with time enough to settle one’s affairs and make peace with God. In Christopher Hamlin’s words, cholera ‘liquefied a body as fluids streamed uncontrollably and insensibly from both ends.’ Put more prosaically, victims had roughly a one in two chance of fitting themselves to death in their own watery shit, within a day or even half a day of infection. Contemporary medicine could do nothing beyond the standard general remedies of brandy, opium, bleeding and purging, and many hospitals sensibly, if cynically, refused to admit infectious patients.
From the perspective of government, cholera could be observed in new and not always reassuring ways. From the late 1830s the General Register Office collected standardised data on births and deaths, which was assimilated by a team of bureaucrats into annual statistical digests. In this sense cholera was the first ‘statistical disease’, and to many this new perspective on the disease merely confirmed its near-supernatural power to spread and to kill. But most of all, cholera seemed to threaten the established social and political order. Nineteenth-century European governments feared revolution on French lines, and cholera brought these fears to a new pitch in an era that also witnessed famines, economic depressions, and the rise of working-class political movements like Chartism. Cholera challenged the power and accountability of a liberal state like Britain, and pointed an accusing finger at the moral squalor of those who (depending upon your political persuasion) let themselves and their families live in filth, or paid their workers so little that they had no choice but to live in filth. In Charles Kingsley’s novel Two Years Ago, published in 1856, one character confesses the meaning of cholera:
I have been a very dirty, nasty fellow. I have lived contented in evil smells, till I care for them no more than my pig does … I have probably been more or less the cause of half my own illnesses, and of three-fourths of the illnesses of my children.
Fittingly, then, the first revolution cholera sparked was not medical but political. By the early 1830s Britain’s Elizabethan Poor Law was coming apart at the seams. This system relied upon individual parishes to provide for their own poor, but in the new industrial cities the density of population and the sheer numbers of paupers made it unworkable. Its replacement – the 1834 New Poor Law – embodied the spirit of laissez-faire capitalism, and the Malthusian concept of poverty as the result of individual moral failure. Under the principle of ‘less eligibility’, life on poor relief would be worse than the worst available job, providing a rational economic incentive for the poor to find work, even if they had to migrate. The dismal quality of poor relief would be guaranteed by providing it only in workhouses – prison-like institutions where the poor would be kept alive, but on the most meagre rations and in the most humiliating circumstances.
Overseeing the New Poor Law was the Poor Law Board, and overseeing the Board was its secretary, Edwin Chadwick: an ambitious young lawyer, often cited as one inspiration for Charles Dickens’ Gradgrind. Chadwick had been involved in drafting the New Poor Law, but he quickly noticed that in practice it did not seem to be working. Intended to reduce the cost of welfare and the numbers of paupers, its costs were rising rapidly, and the workhouses were almost always full; clearly the poor were not being driven back to work. In 1839 Chadwick received a government commission to investigate the lives of the poor, and in 1842 he published his masterwork – the Report on the Sanitary Condition of the Labouring Population of Great Britain. In this long, desiccated book – a Gradgrindian take on Dickens’ double-decker novels – he set out an entirely new way of thinking about poverty, dirt and disease.
For Chadwick, most urban poverty was not the result of individual immorality or laziness. Rather, it was caused by sickness, by ‘filth diseases’ like cholera and typhoid. These ‘filth diseases’ were, in turn, a product of the appalling conditions of modern urban life. Cholera victims were quite literally being poisoned by their surroundings: sewage, refuse, graveyards, and even living human bodies gave off poisonous vapours, ‘miasmas’, which spread through the air. To solve the problem of cholera, and hence the problem of poverty, Chadwick advocated a massive programme of public health reform; clean up the industrial cities, and at a stroke you would remove most disease and hence most poverty.
Chadwick’s miasmatic theory of poverty and disease was one of the most powerful and controversial ideas in mid-nineteenth century Britain, a bureaucratic counterpart to Darwin’s theory of evolution and Marx and Engels’ Communist Manifesto. It inspired a revolution in public health, and was instrumental in persuading British governments that laissez-faire freedoms should be balanced with state intervention. And it is worth observing that at root this was not a medical response to the problem of cholera, but a political and administrative response to the problem of poverty and the threat of revolution. Turning the filthy industrial cities into sanitary paradises was also a way of turning a poor, discontented urban underclass into responsible, contented, hard-working citizens. But Chadwick’s arguments also brought together politics and medicine in striking new ways.
Historians used to characterise the medical history of ‘the cholera years’ as a struggle between two well-defined and opposing groups – miasmatists and contagionists. The story is more complex than this, and we will do better to think in terms of three broad and partially overlapping positions, all of which were already well established in Western medicine. The constitutional view of cholera emphasised a combination of personal and environmental factors – diet, climate, fatigue and so on – that could cause cholera to erupt within the body. As we have seen, this position drew on a long tradition of Western thought, and most mid-nineteenth-century British doctors accepted that some degree of constitutional predisposition was involved in susceptibility to cholera. Contagionism, meanwhile, explained cholera as a distinct kind of matter – a toxin, a poison, a ferment – existing in the environment, which could be spread from person to person by physical contact.
Finally, the miasmatic view, as endorsed by Chadwick, focused on environmental processes like rotting, fermentation or geological decomposition. These processes produced toxic miasmas, which in turn induced cholera when they entered the body. Like constitutionalism, this was an ancient view; since medieval times it had been used to explain the spread of malaria – literally, ‘bad air’. In the 1840s and 1850s it was the most popular model for cholera, and its advantages were numerous. Like each of these three positions, it was rational and materialistic, and could be acted upon in practical ways. It made visceral sense to those who had experienced the nauseating conditions of life in the new industrial cities. It offered a solution to two major problems – disease and poverty – and it did not demand the unpopular and expensive measure of quarantining foreign ships.
But even these three positions don’t quite capture the sheer range of ways in which nineteenth-century physicians thought about cholera. It might, for example, be caused by a miasma, with susceptibility largely determined by constitutional factors, which in turn reflected some greater periodicity in the climate. Miasma itself might be a generic vapour responsible for a wide range of diseases, or a specific poison causing only cholera. But the greatest diversity of opinion was to be found amongst the contagionists. Drawings made by the physician Arthur Hassall – to whom we’ll return – and published in the Lancet in 1850-51 seemed to suggest that cholera might be caused by some kind of microscopic life. But what kind? A worm, a yeast, a rotifer, a microbe? Or an inorganic poison, a toxin, a self-reproducing ferment? Until the laboratory bacteriology of Robert Koch and Louis Pasteur became widely accepted a generation later, there were no standardised techniques for classifying, isolating and studying microscopic life, and no protocols for getting the results accepted by a community of researchers. It was largely a matter of microscopists comparing drawings of what they had seen through their lenses; not surprisingly, they rarely agreed. In a typical scenario, repeated dozens of times, a microscopist would announce that he had identified the microbe that caused cholera. This would be followed by a torrent of criticism from other microscopists, who claimed to have observed the same microbe in healthy individuals, or seen cases of cholera where the microbe was not present, and would end with a shame-faced withdrawal of the announcement.
What now seems to be the most empirical explanation for cholera appeared at the time to be a blur of hypothesis, speculation and wishful thinking. How could this continent-crossing disease be caused by tiny, fleetingly glimpsed, possibly animate specks of matter? If these contagious particles could be found everywhere, how did anyone escape death by water, or by air? And how could they kill organisms billions of times larger than themselves? It was within this remarkable political and intellectual milieu, this din of squabbling iconoclasm, radical reform, and rolling Victorian prose, that John Snow began his work on cholera.
Snow’s first encounter with Asiatic cholera took place long before he set up shop in Soho. At the age of 14 Snow had been apprenticed to the Newcastle surgeon William Hardcastle. At the time of the first cholera epidemic in 1831 – the epidemic in which William Sproat died, only a few miles away – Hardcastle and the eighteen-year-old Snow were working at the Killingworth colliery. Snow did not record his experiences at Killingworth, but in the second edition of his pamphlet on cholera he included a description, supplied by a relative, of conditions in a colliery near Leeds:
I fear that our colliers are no better than others as regards cleanliness. The pit is one huge privy, and of course the men always take their victuals with unwashed hands.
Having completed his apprenticeship, Snow set out for London on foot, first crossing the Pennines to visit a relative in Liverpool, then making for the capital via Bath. In October 1836 he enrolled in the Hunterian School of Medicine in Soho, and in 1844 received his MD from the University of London. But Snow, like many poor students, had entered practice early on. By 1840, having gained licenses from the Royal College of Surgeons and the Society of Apothecaries, he established a general practice at 54 Frith Street, in the heart of Soho.
It is no coincidence that Snow’s work on cholera took place against the backdrop of London’s liveliest and filthiest district. From its origins as a genteel West End suburb in the seventeenth century, Soho had always been seen as different: foreign, subversive and seductive, embodying London’s confused attitudes towards pleasure and pain, cleanliness and dirt – not only physical filth, but also moral and political pollution. By the mid-nineteenth century Soho was poor and dirty, but industrious; trade directories of the period reveal grocers, bonnet-makers, bakers, tailors, masons, shoemakers, brewers and many other artisan trades jostling for space with nuns, prostitutes, and exiled dissidents like Karl Marx. Space, however, was one thing they could not manufacture, and it was not unusual for Soho’s residents to sleep five or six to a room. And like all Londoners, they faced a pressing problem: how to get rid of their excrement?
For centuries most London houses had cesspits in the basement, which were emptied regularly by the ‘night-soil men’. (Much of this ‘night-soil’ was used to manure the farms and market gardens that grew the city’s food, a gift for satirists who depicted London as a monster feeding on its own excrement.) Through the early nineteenth century water-closets, and the sewers they necessitated, became more popular. When the 1848 Nuisances Removal and Contagious Diseases Prevention Act banned cesspools and required all existing buildings to have sewer connections, the effect was swift and appalling. In the words of Joseph Bazalgette, the man who rebuilt London’s sanitation system in the 1860s and 1870s:
[W]ithin a period of about six years, thirty thousand cesspools were abolished, and all house and street refuse was turned into the river.
Until the 1820s the Thames had been a comparatively clean river, and a number of private water companies pumped water directly from the river, in its natural – we might say ‘untreated’ – state, into the homes of their customers. By the early 1850s, the river was filled with sewage, churned back and forth by two tides a day. Arthur Hassall provided a pithy summary of this situation:
According to the present system of London Water Supply, a portion of the inhabitants of the metropolis are made to consume, in one form or another, a portion of their own excrement, and, moreover, to pay for the privilege.
In this regard, however, Soho’s residents saw themselves as lucky. Few of them could afford piped water, but in the parish of St Luke’s they had a good number of communal street pumps. One of these – the Broad Street pump – was deeper than most London wells, and its water was favoured not only by private households but also by local coffee shops and pubs, right through the second British cholera epidemic in 1848-49.
By the time of this second epidemic Snow had been working in Soho for almost a decade. He ministered as best he could to its victims, and this appears to have been the experience that prompted him to publish on the subject. A 32-page pamphlet, titled On the Mode of Communication of Cholera and printed privately in August 1849, set out the bones of Snow’s thesis. Cholera was a local infection of the bowels, caused by the consumption of materies morbi – ‘disease-causing particles’. And, following this, it was spread by drinking water contaminated with the faeces of cholera victims.
There are many questions we might want to ask about this argument. What convinced Snow that dirty water, rather than dirty air, was responsible for the communication of cholera? We have little direct evidence beyond Snow’s published writings, and in them he writes that a consideration of cholera pathology first led him to reject a miasmatic model of transmission. If cholera entered the body through the lungs, one might expect its major symptoms to be respiratory, not intestinal. To this we can add two educated guesses. We know that Snow followed political debates over the deteriorating quality of Thames water in the late 1840s. The 1848-49 epidemic coincided with the banning of cesspits, and this may have suggested the notion of a water-borne cycle of contamination. In the same period he was also investigating the principles of anaesthetics, and his knowledge of the gas laws may have made the idea of a widely diffused airborne miasma with the power to kill seem unconvincing.
More important, perhaps, is the question of what Snow meant by materies morbi. This highlights one of the great difficulties for modern readers of his work. Modern medicine tells us that Snow’s insight about the mode of communication of cholera was in essence correct; cholera is indeed an infectious disease of the gastro-intestinal tract, transmitted faeco-orally. It is tempting to jump from this observation to the conclusion that Snow must have anticipated all the principles of modern bacteriology a generation before the first versions of germ theory were widely accepted. Read what Snow actually wrote, however, and it becomes clear that his materies morbi were not bacteria in the post-Pasteur, post-Koch sense. In many ways they had much in common with miasmas.
Much of what became germ theory emerged from attempts by chemists in the 1830s and 1840s to understand enviromental processes like putrefaction and fermentation. One of the most widely discussed explanations was the ‘zymotic’ theory, promoted by the German chemist Justus von Liebig. Liebig argued that these processes were a kind of molecular chain reaction, spread by large organic molecules coming into contact with one another and breaking down into smaller ‘zymes’. In many ways this was more a useful metaphor than a practical theory: these hypothetical zymes could not be found in laboratories or sewers or microscope slides. But zymotic theory provided a new basis for both miasmatic and contagionist models of disease, and provided a further rationale for cleaning up the dirty industrial cities.
Snow’s thinking on cholera was strongly influenced by Liebig’s work, and his materies morbi are best understood as zymes – small organic molecules with the power of transmitting a particular form of decomposition. In his 1849 pamphlet he specifically rejected the notion that ‘cholera depends upon veritable animals, or even animalcules’. Rather, he looked to ‘the continuity of molecular changes, by which combustion, putrefaction, fermentation, and the various processes in organised beings, are kept up.’ Seen in this light, Snow’s work is more clearly of its time: a modification of a prevailing theory, indeed one that might be interpreted as a kind of waterborne miasma, and which was best met with better personal hygiene and improvements in the working conditions of miners and labourers.
But the biggest question we might want to ask is why Snow’s first pamphlet met with near-universal indifference. Here, again, a perspective based on modern medical knowledge is misleading, suggesting that only ignorance, indolence or malice could have been to blame. In fact, there were many strong reasons why Snow’s work did not gain widespread attention. Between 1845 and 1856 more than seven hundred books and pamphlets dealing with cholera were published in London alone. Some were the work of racists, religious fanatics or quacks, but others were written by respectable physicians and surgeons. A slim, self-published volume by an obscure general practitioner working in a poor part of the city was not likely to stand out in this over-stuffed market.
More than this, Snow’s status in London’s medical landscape was equivocal. Though a committed member of the Westminster Medical Society and the Medical Society of London, he never held a university or a public health post. His work on anaesthesia was increasingly respected, but he had also acquired a reputation as something of a crank. This was, after all, a man who had spent more than a decade as a vegetarian and teetotaller, preferences that looked like madness if not treason to many of his beef-eating, beer-swilling contemporaries. And he had a taste for picking holes in other people’s work. Thomas Wakley, editor of the Lancet, published many of Snow’s letters and articles, but also warned that ‘Mr Snow might better employ himself in producing something, than in criticising the productions of others.’
Those who did read Snow’s pamphlet found his claims interesting but speculative, and his evidence unconvincing. One of the few reviews, published in the London Medical Gazette, criticised the absence of a truly convincing experimentum crucis – an instance that would prove beyond doubt that cholera was transmitted by water. Reflecting on the failure of his first cholera pamphlet, Snow helped to found the new Epidemiological Society of London, thought about his experimentum crucis, and waited.
On the night of 31st August 1854 more than a dozen Soho residents came down with symptoms of cholera; so began one of the most intense outbreaks in London’s history. Within a fortnight more than five hundred people had died, most in the neighbourhood of Broad Street and nearby Golden Square, and many more fled the area. Snow did what he could for his patients, but he also took a second look at the local water supply. A sample from the Broad Street pump on 3rd September seemed more pure than most London well-water, but Snow noted ‘small white flocculent particles’. A microscopic examination by Arthur Hassall, made at Snow’s request, showed ‘that these particles had no organised structure, and … probably resulted from decomposition of other matter’, while ‘a great number of very minute oval animalcules’ were ‘of no importance’.
Undaunted, Snow obtained a list of cholera deaths and their addresses in the first few days of the outbreak. Door-to-door enquiries on 6th September showed that eighty-three percent of the dead had been in the habit of drinking water from the Broad Street pump. Snow took this information and his material from the first pamphlet to an emergency meeting of the parish Board of Guardians on the evening of 7th September. In the face of much opposition, he convinced them that the pump should be disabled. The following morning, the pump handle was removed.
Snow was never in any doubt that this action was essentially symbolic, writing that cholera cases had ‘far diminished before the use of the water was stopped’. Reverend Henry Whitehead, the curate of St Luke’s, agreed:
It is commonly supposed and sometimes asserted even at meetings of Medical Societies that the Broad Street outbreak of cholera in 1854 was arrested in mid-career by the closing of the pump in that street … [T]his is a mistake … the outbreak had already reached its climax, and had been steadily on the decline for several days before the pump-handle was removed.
In the months after the end of the outbreak, Snow drew up a new edition of On the Mode of Communication of Cholera. He would analyse two ‘natural experiments’ – one based on the Soho outbreak, the other examining the wider impact of the 1853-54 epidemic in London. These would, he believed, create a truly convincing case for dirty water as the mode of cholera transmission.
Snow’s first ‘natural experiment’ was a detailed, near-forensic study of the Soho outbreak. Extensive detective work revealed a series of suggestive anomalies. Residents of the parish workhouse had a low incidence of cholera; they had their own separate well. Workers at the Lion Brewery also rarely succumbed; their water was supplied by the New River Company (a Jacobean conduit bringing water from springs in Hertfordshire), and they tended to drink their own beer for refreshment. Most impressively, Snow found a distant and isolated case of cholera that could be linked directly to the Broad Street pump. Susannah Eley, the widow of a man who had founded a percussion-cap factory on Broad Street, had retired to Hampstead, but had taken with her a taste for water from the pump. Her relatives sent barrels of it to her lodgings; the last delivery arrived on 31st August; she drank it, and died on 2nd September. This was, he wrote, his experimentum crucis – a case of cholera in a district where it was not previously known, and which could be linked to consumption of water from the presumed source of the disease. Snow also used information from the Soho outbreak to create a striking visual representation of the epidemic, one that has become a symbol of his work. He marked cases of cholera on a map of Soho, using bar lines to indicate the number of deaths in each house. This showed that cases clustered around Broad Street and the pump, and that, broadly speaking, the incidence of the disease decreased as distance from the pump increased.
His second ‘natural experiment’ was, in his words, ‘on the grandest scale’, taking in:
[N]o fewer than three hundred thousand people of both sexes, of every age and occupation, and of every rank and station, from gentlefolks down to the very poor …
It was based on an observation Snow had made during the 1848-49 epidemic – that death rates were particularly high in south London. Two water companies – the Lambeth and the Southwark and Vauxhall – supplied most districts south of the Thames, and in 1849 they had both drawn their water from the polluted stretch of riverside at Battersea Fields. In 1852, however, the Lambeth had moved its waterworks to Thames Ditton, upstream of London and hence far less polluted.
A comparison of the death rates amongst customers of these two companies during the first seven weeks of the 1854 epidemic showed that, of 44 households suffering cholera deaths, 38 had been supplied by the Southwark and Vauxhall. Snow sent his results to William Farr, statistician to the Registrar-General for Births, Marriages and Deaths. Though Farr did not immediately accept Snow’s arguments about cholera, he was struck by his data, and ordered his registrars in all southern districts of London to include details of water supply in their returns for cholera deaths. Both companies supplied customers in the same areas, often to different houses in the same street. Though this made data analysis tricky, it provided a kind of natural randomisation, helping to minimise the effects of factors such as air quality, wealth, and general cleanliness. Snow’s final analysis showed that those who drank the polluted water of the Southwark and Vauxhall were eight to nine times more likely to die of cholera than those who drank the comparatively cleaner water of the Lambeth.
In the spring of 1855 the second edition of On the Mode of Communication of Cholera, much enlarged but, again, privately printed, went on sale. Snow repeated his central theses about the transmission of cholera, described his two ‘natural experiments’, and set out a list of recommendations, the eighth and ninth of which were:
To effect good and perfect drainage.
To provide an ample supply of water quite free from contamination with the contents of sewers, cesspools, and house-drains.
This second edition elicited a little more attention than the first; only a little more, however, and much of it critical. The most detailed critique came from Edmund Parkes, Professor of Clinical Medicine at University College London, and an experienced pathologist and epidemiologist who had witnessed cholera in the Crimea and India. Parkes welcomed Snow’s demonstration that polluted water was an important factor in the transmission of cholera. But he did not accept that polluted water alone was responsible. Snow had assumed, rather than proved, that cholera was mono-causal, and this created a fatal weakness in his argument.
Take, for instance, Snow’s experimentum crucis – the ‘Hampstead Widow’, Susannah Eley. Snow claimed that this case was unanswerable, but he had not examined other factors that might have been involved in her death, nor had he made an effort to track down all distant users of the Broad Street pump as comparators. Taken as a single case, it was highly suggestive, but hardly conclusive. Parkes also found inconsistencies in Snow’s statistical work, and pointed out other questions he had not addressed. Where were these materies morbi? Analysis of water from the Broad Street pump had shown nothing that resembled a cholera pathogen; indeed, the water appeared to be cleaner than average. How had the pump become contaminated in the first place, and why had its virulence apparently declined after a week or so? Snow, in short, had not met the high standards of proof he had set for himself.
This scepticism was reflected in an official investigation of the Soho outbreak, carried out by the General Board of Health under Edwin Chadwick. The Board dismissed Snow’s evidence, along with the possibility that the outbreak could be traced back to the Broad Street pump, and the pump handle was replaced. A private ‘Cholera Investigation Committee’, led by the microscopist Edwin Lankester, produced a report challenging this official refutation, with sections by Snow and by the Reverend Henry Whitehead. Whitehead had initially found Snow’s work unconvincing, but swiftly changed his mind, and the two men became friends. Whitehead also discovered a potential source for the contamination of the pump. Records showed that on 2nd September 1854 an infant had died of diarrhoea in the house closest to the pump. The child had been sick since 28th August – three days before the outbreak began. Its mother, Sarah Lewis, had rinsed soiled nappies and emptied the water into a cesspit in the cellar. On inspection, the brickwork of this cesspit was found to be decayed; contaminated water could easily have seeped through into the pump well, only three feet beyond it. An episode that killed more than five hundred people began, it seems, with the death of a nameless child.
Within three years Snow himself was dead. On 10th June 1858 he was found unconscious at his desk, having suffered a stroke. He lingered for a week before dying at the age of forty-five. By the time of his death British public health was changing, and the genial diplomat John Simon had replaced the autocratic doctrinaire Edwin Chadwick. Simon pursued a broad-based programme of epidemiological research and sanitary reform, overseeing the reconstruction of London’s sewerage system by Joseph Bazalgette. In his English Sanitary Institutions, published in 1890, long after his retirement, Simon praised Snow’s work as ‘probably … still the most important truth yet acquired by medical science for the prevention of epidemics of cholera’.
In paying this handsome posthumous tribute Simon retrospectively extended his policy of building an inclusive medical and political consensus. Equally, however, he was well aware that Snow’s work had had little influence on the course of British public health in the decades after his death. Medical thought gradually converged around the idea that cholera was ‘a fecal disease caused by a specific agent’, particularly after the last British epidemic in 1866. William Farr became convinced that the disease was water-borne, and a Lancet editorial in the same year proclaimed that:
The researches of Dr Snow are among the most fruitful in modern medicine … We owe to him chiefly the severe induction by which the influence of the poisoning of water-supplies was proved.
But most doctors (including Simon) continued to accept a multi-causal model in which contaminated water was one of many factors, and invisible materies morbi were still a hypothesis. The physician Henry Acland, for example, studied a cholera outbreak in Oxford in 1854, and came to the conclusion that it could be transmitted by water. But Acland also argued that the cholera poison originated in the atmosphere, possibly from electrical discharges during thunderstorms.
Even if Snow’s contemporaries had accepted his conclusions in 1854-55, it is not clear what practical difference this would have made. Without Snow’s influence, a movement to improve London’s water quality was already under way by the mid-1850s, along with a more general effort to clean up the industrial cities. Bazalgette’s immense project, begun in 1858 and completed in 1875, included filtration of drinking water and the complete separation of fresh water and sewage. But this was rooted in Simon’s broad sanitarian consensus, refracted through the concerns of contemporary politics and the mighty capabilities of mid-Victorian civil engineering. It had not been provoked by a revelation that cholera was transmitted by dirty water alone. Indeed, a public health movement concentrating on dirty water might have lacked the wider environmental gaze of Simon’s sanitary reform. In his evidence to a parliamentary committee in 1855 Snow had argued that, since filth diseases were not spread by poisonous vapours, there was no need to restrict ‘noxious trades’ and factory chimneys. And when Robert Koch announced the identification of Vibrio cholera in 1883 – the single most important step in establishing the modern bacteriological view of cholera, though one anticipated by an obscure Florentine doctor, Filipo Pacini, in the 1850s – his paper did not mention Snow. On the Mode of Communication of Cholera had, in Christopher Hamlin’s words, ‘disappeared into the black hole that swallowed cholera publications’.
But Snow never disappeared entirely. His studies were cited, from time to time, in textbooks of public health and epidemiology published in Britain and the US – books like William Sedgwick’s Principles of Sanitary Science, published in 1901. His rediscovery, and the beginning of the process that turned him into the ‘founding father of epidemiology’, is usually dated to 1936, when Wade Hampton Frost, first Professor of Epidemiology at Johns Hopkins, republished the second edition of On the Mode of Communication of Cholera. Frost was motivated not by mere historical curiosity, but by urgent professional concerns. At the time epidemiology was seen as a poor relation of bacteriology. By setting out a ‘useable past’, and by presenting Snow as a heroic founding figure who had used pioneering epidemiological work to end an epidemic, Frost sought to raise the relative status of his discipline, and to make a case for its importance in modern urban life. A subsequent generation of epidemiologists took up Frost’s version of Snow, and this myth-making has continued. Several textbooks published in the US in the 1950s and 1960s, for example, silently altered his map, making it appear closer to the principles of contemporary epidemiology. In giving Snow the recognition we now think he merits, we have, it seems, tried repeatedly to improve on the facts of his life. A desire to promote evidence-based medicine has overshadowed the truths of evidence-based history.
I began this essay with a paradox, and I want to end with one that, to me, seems even more striking – the central paradox of Snow’s life. The more we examine the cultural and political background to the cholera years, the more we grasp the fear and panic, the hatred and division, this disease provoked, the more we can (if we are so minded) appreciate Snow’s courage, dedication and clear, independent thinking. He demonstrated, in ways that retrospectively seem compelling and original, the connection between cholera and contaminated water. In doing so, we may think, he should also have publicly validated new notions of scientific medicine, specific disease causation, and the importance of public health reform rooted in epidemiology, and changed the course of medical history. But he did not.
In one sense, the problem of cholera in the nineteenth century was an epidemiological and pathological puzzle, to be solved – as Snow tried to solve it – with shoe leather, statistics and flashes of clinical insight. But it was also far more than this. The problem of cholera was the problem of free trade and the fate of liberalism. It was the problem of governing industrial capitalism, and living in industrial cities. It was the problem of maintaining imperial control and global military and naval power. It was the problem of the origin and nature of poverty. It was the problem of the proper roles for science and medicine in government and public life. In this larger, political sense, Snow did not solve the problem of cholera. It is ironic, and telling, that many of these problems were solved not by physicians wielding microscopes and germ theories, but by lawyers, administrators and engineers who thought that cholera blew on the wind.
William F. Bynum, Science and the Practice of Medicine in the Nineteenth Century (Cambridge University Press, 1994).
Richard J. Evans, ‘Epidemics and revolutions: cholera in nineteenth-century Europe’, Past and Present 120 (1988), 123-146
Christopher Hamlin, A science of impurity: water analysis in nineteenth-century Britain (University of California Press, 1990)
Christopher Hamlin, Cholera: the biography (Oxford University Press, 2009)
Kari S. McLeod, ‘Our sense of Snow: the myth of John Snow in medical geography’, Social Science & Medicine 50 (2000), 923-935
R.J. Morris, Cholera 1832: the social response to an epidemic (Croom Helm, 1976)
Charles Rosenberg, ‘Cholera in nineteenth-century Europe: a tool for social and economic analysis’, Comparative Studies in Society and History 8 (1966), 452-463
John Snow, On the Mode of Communication of Cholera (privately printed; first ed. 1849, second ed. 1855)
Stephanie Snow, Operations without pain: the practice and science of anaesthesia in Victorian Britain (Palgrave Macmillan, 2006)
Stephanie Snow, ‘John Snow: the making of a hero?’, Lancet 372 (2008), 22-23
Peter Vinten-Johansen et al, Cholera, chloroform and the science of medicine: a life of John Snow (Oxford University Press, 2003)
Mick Worboys, Spreading germs: disease theories and medical practice in Britain, 1865-1900. (Cambridge University Press, 2000)
John Snow Archive & Research Companion (http://johnsnow.matrix.msu.edu/)
‘John Snow – a historical giant in epidemiology’, UCLA Department of Epidemiology School of Public Health (www.ph.ucla.edu/epi/snow.html)