The Ghost Map

by Steven Johnson

  The Vestry Committee’s verdict meant that for the first time an official committee investigation had endorsed the waterborne theory. It was a small victory, since the vestry had no power over public-health issues outside Soho, but it gave Snow and his future allies something that Snow had long sought: an official endorsement. In the years and decades that followed, the Vestry Committee report grew in influence as the story of the Broad Street outbreak was re-told. Slowly, over time, it occluded the Board of Health investigation altogether. The twelve pages devoted to Broad Street in Sedgwick’s Principles of Sanitary Science and Public Health quote extensively from the Vestry report, while the Board of Health verdict goes unmentioned. The vast majority of the retellings of the Broad Street case fail to mention the signal fact that among the public-health authorities of the day, Snow’s investigation was of no significance.

  Rewinding the tape of history and imagining alternative scenarios is always a fanciful exercise, but it can be instructive. If the Vestry Committee had not endorsed the waterborne theory, then the Broad Street episode would likely have entered the historical record as yet another example of miasma’s deadly reach: a crowded, unsanitary neighborhood suffused with hideous smells that got its comeuppance. Snow’s interventions would have remained the work of an illustrious maverick, an outsider with an unproven theory who failed to convince anyone other than a panicked Board of Governors that had removed a pump handle out of desperation. No doubt science would ultimately have come around to the waterborne theory, but it might well have taken decades longer without the clarity and reproducibility of the Broad Street story and its accompanying map. How many thousands more might have died in that interval?

  It is a subtle chain of causal connections, but a plausible one nonetheless. The map helps tip Whitehead toward the waterborne theory, which prods him to discover the index case, which necessitates the second excavation, which ultimately tips the Vestry Committee toward Snow’s original theory. And the endorsement of the Vestry Committee rescues Broad Street from the side of the miasmatists. It becomes the most powerful and seductive proxy for Snow’s waterborne theory, thus accelerating the adoption of the theory by the very same public-health institutions that had renounced it so thoroughly at the time of the outbreak. The map may not have persuaded Benjamin Hall of the dangers of contaminated water in the spring of 1855. But that doesn’t mean it didn’t change the world in the long run.

  Imagining the chain of events this way makes one fact overwhelmingly clear: John Snow may have been instrumental in first identifying the pump as the likely culprit behind the outbreak, but Whitehead ultimately supplied the crucial evidence for establishing the pump’s role. The shorthand version of the Broad Street case invariably settles on the image of the visionary scientist, working alone against the dominant paradigm, discovering the secret cause behind a terrible plague. (Whitehead is often mentioned in popular accounts, but usually as a sort of dutiful apprentice, helping Snow with the door-to-door surveys.) But Broad Street should be understood not just as the triumph of rogue science, but also, and just as important, as the triumph of a certain mode of engaged amateurism. Snow himself was a kind of amateur. He had no institutional role where cholera was concerned; his interest in the disease was closer to a hobby than a true vocation. But Whitehead was an amateur par excellence. He had no medical training, no background in public health. His only credentials for solving the mystery behind London’s most devastating outbreak of disease were his open and probing mind and his intimate knowledge of the community. His religious values had brought him into close contact with the working poor of Soho, but they had not blinded him to the enlightenments of science. If part of the significance of Snow’s second map lay in the way it empowered the community to represent itself, Whitehead was the conduit that made that representation possible. Whitehead was not an expert, an official, an authority. He was a local. That was his great strength.

  And here lies an antidote of sorts to the horror of Broad Street, to the grisly image of entire families dying together in their single-room flats: the image of Snow and Whitehead building an unlikely friendship in those late winter months of 1855, drawn together by a terrible outbreak of disease in their neighborhood and, ironically, by Whitehead’s initial skepticism about Snow’s theory. We know very little about the personal interaction between the two men, beyond the crucial data they exchanged, beyond Snow’s sharing of his monograph, and his prophetic statements about the future of cholera. But it is clear from Whitehead’s subsequent recollections that a powerful bond formed between them—the quiet, awkward anesthesiologist and the compulsively social curate—a bond forged both by living through an urban battleground of unimaginable terror, but also by jointly unearthing the secret cause behind the carnage.

  This is not mere sentimentality. The triumph of twentieth-century metropolitan life is, in a real sense, the triumph of one image over the other: the dark ritual of deadly epidemics replaced by the convivial exchanges of strangers from different backgrounds sharing ideas on the sidewalk. When John Snow first stepped up to the Broad Street pump in early September 1854, it was by no means clear which image would be victorious. London seemed to be destroying itself. You could leave town for a weekend and come back to find ten percent of your neighbors being wheeled down the street in death carts. That was life in the big city.

  Snow and Whitehead played a small but defining role in reversing that trend. They solved a local mystery that led, ultimately, to a series of global solutions—solutions that transformed metropolitan living into a sustainable practice and turned it away from the collective death drive that it threatened to become. And it was precisely their metropolitan connection that made this solution possible: two strangers of different backgrounds, joined by circumstance and proximity, sharing valuable information and expertise in the public space of the great city. The Broad Street case was certainly a triumph of epidemiology, and scientific reasoning, and information design. But it was also a triumph of urbanism.

  John Snow would never get to experience that triumph in its entirety. In the first few years that followed the outbreak, supporters of the waterborne theory grew in number and in visibility. Snow’s monograph had included both the Broad Street case and the South London water-supply study, and the combination seemed to produce converts at a much greater clip than the original monograph had six years before. John Sutherland, prominent inspector for the Board of Health, made several public statements that offered at least a partial endorsement of the waterborne theory. William Farr’s Weekly Returns grew increasingly supportive of the theory. Several publications appeared that argued for the waterborne theory without crediting Snow for the original insight—including a few that credited William Budd with the discovery of cholera’s waterborne nature. Perhaps aware that his legacy would ultimately revolve around his cholera investigations, Snow responded to these papers with politic, but firm, letters to the medical journals, reminding his colleagues of his precedence in these matters.

  Still, miasma retained its hold over many, and Snow himself was often subjected to derisive treatment by the scientific establishment. In 1855, he gave his testimony in Parliament on behalf of the “offensive trades” before a committee on the Nuisances Removal Act. Snow argued eloquently that infectious diseases were not spread through the foul smells emitted by the bone-boilers and gut spinners and tanners of industrial London. Again, he drew upon reasoned statistical analysis, arguing that the laborers who worked in these establishments would have had a much greater incidence of disease than the general public if the miasma were somehow breeding epidemics. The fact that they did not show a disproportionate rate of contagion—despite their immersion in the fumes—meant that the cause of disease lay elsewhere.

  Benjamin Hall, ever the miasmatist, expressed open disbelief at Snow’s testimony. Edwin Chadwick would shortly after denounce Snow’s reasoning as illogical. But the real assault would come in an unsigned editorial in The Lancet that tore into Snow with remark
able fury and disdain:

  Why is it, then, that Dr. Snow is so singular in his opinion? Has he any facts to show in proof? No!… But Dr. Snow claims to have discovered that the law of propagation of cholera is the drinking of the sewage-water. His theory, of course, displaces all other theories. Other theories attribute great efficacy in the spread of cholera to bad drainage and atmospheric impurities. Therefore, says Dr. Snow, gases from animal and vegetable decomposition are innocuous! If this logic does not satisfy reason, it satisfies a theory; and we all know that theory is often more despotic than reason. The fact is, that the well whence Dr. Snow draws all sanitary truth is the main sewer. His specus, or den, is a drain. In riding his hobby very hard, he has fallen down through a gully-hole and has never since been able to get out again.

  The confidence of the miasmatists couldn’t last forever. In June 1858, a relentless early-summer heat wave produced a stench of epic proportions along the banks of the polluted Thames. The press quickly dubbed it the “Great Stink”: “Whoso once inhales the stink can never forget it,” the City Press observed, “and can count himself lucky if he live to remember it.” Its overwhelming odors shut down Parliament. As the Times reported on June 18:

  What a pity… that the thermometer fell ten degrees yesterday. Parliament was all but compelled to legislate upon the great London nuisance by the force of sheer stench. The intense heat had driven our legislators from those portions of their buildings which overlook the river. A few members, bent upon investigating the matter to its very depth, ventured into the library, but they were instantaneously driven to retreat, each man with a handkerchief to his nose.

  But a funny thing happened when William Farr calculated his weekly returns for those early weeks of June. The rates of death from epidemic disease proved to be entirely normal. Somehow the most notorious cloud of miasmatic air in the history of London had failed to produce even the slightest uptick in disease mortality. If all smell was disease, as Edwin Chadwick had so boldly pronounced more than a decade before, then the Great Stink should have conjured up an outbreak on the scale of 1848 or 1854. Yet nothing out of the ordinary had happened.

  It’s easy to imagine John Snow taking great delight in the puzzling data from the Weekly Returns, perhaps writing up a brief survey for The Lancet or the London Medical Gazette. But he never got the opportunity. He had suffered a stroke in his office on June 10, while revising his monograph on chloroform, and died six days later, just as the Great Stink was reaching its peak above the foul waters of the Thames. He was forty-five years old. More than a few friends wondered if his many experiments inhaling experimental anesethetics in his home lab had brought on his sudden demise.

  Ten days later, The Lancet ran this brief, understated item in its obituary section:

  DR. JOHN SNOW—This well-known physician died at noon on the 16th instant, at his house in Sackville-street, from an attack of apoplexy. His researches on chloroform and other anaesthetics were appreciated by the profession.

  Snow might have hoped that cholera would prove central to his legacy, but in the first obituary that ran after his death it didn’t even warrant a mention.

  AFTER YEARS OF BUREAUCRATIC WAFFLING, THE GREAT STINK finally motivated the authorities to deal with the crucial issue that John Snow had identified a decade before: the contamination of the Thames water from sewer lines emptying directly into the river. The plans had been in the works for years, but the public outcry over the Great Stink had tipped the balance. With the help of the visionary engineer Joseph Bazalgette, the city embarked on one of the most ambitious engineering projects of the nineteenth century: a system of sewer lines that would carry both waste and surface water to the east, away from Central London. The construction of the new sewers was every bit as epic and enduring as the building of the Brooklyn Bridge or the Eiffel Tower. Its grandeur lies belowground, out of sight, and so it is not invoked as regularly as other, more iconic, achievements of the age. But Bazalgette’s sewers were a turning point nonetheless: they demonstrated that a city could respond to a profound citywide environmental and health crisis with a massive public-works project that genuinely solved the problem it set out to address. If Snow and Whitehead’s Broad Street investigation showed that urban intelligence could come to understand a massive health crisis, Bazalgette’s sewers proved that you could actually do something about it.

  North of the Thames, the plan for the new sewers involved three main lines, each at different levels of elevation, running eastward parallel to the river. On the south side, there were to be two main lines. All the city’s existing surface water and waste lines would empty into one of these “intercepting” sewers, and the contents would then flow—and in some cases be pumped—several miles east of the city. On the north side, they drained into the Thames at Barking; on the south, the outfalls were located at Crossness. The sewers only discharged into the Thames during high tide, after which the seaward pull of low tide would flush the city’s waste out to the ocean.

  It was a demonically complicated undertaking, given that the city already had a complicated infrastructure of pipes and rail stations and buildings—not to mention a population of nearly three million people—that Bazalgette somehow had to work around. “It was certainly a very troublesome job,” he would later write, with typical English understatement. “We would sometimes spend weeks in drawing out plans and then suddenly come across some railway or canal that upset everything, and we had to begin all over again.” Yet somehow, the most advanced and elaborate sewage system in the entire world was largely operational by 1865. The numbers behind the project were staggering. In those six years, Bazalgette and his team had constructed eighty-two miles of sewers, using over 300 million bricks and nearly a million cubic yards of concrete. The main intercepting sewers had cost only £4 million to construct, which would be roughly $250 million today. (Of course, Bazalgette’s labor costs were much cheaper than today’s.) It remains the backbone of London’s waste-management system to this day. Tourists may marvel at Big Ben or the London Tower, but beneath their feet lies the most impressive engineering wonder of all.

  The best way to appreciate the scale of Bazalgette’s achievement in person is to stroll along the Victoria or Chelsea embankments on the north side of the river, or along the Albert Embankment on the southern shore. Those broad, attractive esplanades were built to house the massive low-elevation interception lines that ran parallel to the Thames. Beneath the feet of those happy riverside pedestrians enjoying the view and the open air, beneath the cars hurtling along north of the river, there lies a crucial, hidden boundary, the last line of defense that keeps the city’s waste from reaching the city’s water supply.

  That low-elevation northern sewer was one of the final lines to be completed, and the delays in building it turned out to play a determining role in London’s last great outbreak of cholera. In late June 1866, a husband and wife living in Bromley-by-Bow in East London fell ill with cholera and died a few days later. Within a week a terrible outbreak of cholera erupted in the East End—the worst the city had seen since the ravages of 1853–1854. By the end of August, more than four thousand people had died. This time it was William Farr who did the first round of detective work. Puzzled by the sudden explosion of cholera in the city after a decade of relative dormancy, Farr thought of his old sparring partner, John Snow, and his surveys of the South London water companies that had brought Snow so regularly to the Registrar-General’s Office. Farr decided to break down these new deaths along water-supply lines, and when he did, the pattern was unmistakable. The great majority of the dead had been customers of the East London Water Company. This time around, Farr wouldn’t waste time with miasmatic objections. He didn’t know how the East London supply had been contaminated, but clearly there was something deadly in that water. To waste time would be to condemn untold thousands to their deaths. Farr immediately ordered that notices be posted in the area advising residents not to drink “any water which has not been previously boiled.�
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  Still, mysteries remained. Bazalgette’s sewers were supposed to have cut off the fatal feedback loop between London’s outputs and inputs, its waste and its water supply. And the East London Water Company claimed to use extensive filtering at all of its reservoirs. If some contaminant had somehow made its way out of the city’s sewers, it should have been picked up by the East London filters before being passed on to the wider population. Farr sent a letter to Bazalgette, who immediately wrote back, apologetically, to say that the drainage system in that part of the city had not been activated yet. “It is unfortunately just the locality where our main drainage works are not complete,” he explained. The low-level sewer had been constructed, but Bazalgette’s contractors had yet to finish the pumping station required to elevate the sewage so that gravity could continue to pull it down toward its ultimate outfall at Barking. And so the intercepting line in that area was not in use yet.

  Attention then turned to the East London Water Company. Initially, company representatives swore that all their water had been run through state-of-the-art filter beds at their new covered reservoirs. But reports had surfaced of some customers discovering live eels in their drinking water, which suggested that the filters were not perhaps working optimally. An epidemiologist named John Netten Radcliffe had been assigned to investigate the outbreak, and he began looking into the filtering system in place at East London. Only a few months before, Radcliffe had read a memoir of the Broad Street outbreak authored by a curate who had played some role in the investigation. In the absence of John Snow, it occurred to Radcliffe that this individual might bring some valuable experience to this latest epidemic. And so the amateur epidemiologist Henry Whitehead was brought back to help solve one last case of poisoned water.