The Ghost Map: The Story of London's Most Terrifying Epidemic--and How It Changed Science, Cities, and the Modern World

by Steven Johnson

A Klee painting named “Angelus Novus” shows an angel looking as though he is about to move away from something he is fixedly contemplating. His eyes are staring, his mouth is open, his wings are spread. This is how one pictures the angel of history. His face is turned toward the past. Where we perceive a chain of events, he sees one single catastrophe which keeps piling wreckage and hurls it in front of his feet. The angel would like to stay, awaken the dead, and make whole what has been smashed. But a storm is blowing in from Paradise; it has got caught in his wings with such a violence that the angel can no longer close them. The storm irresistibly propels him into the future to which his back is turned, while the pile of debris before him grows skyward. This storm is what we call progress. —Walter Benjamin, “Theses on the Philosophy of History”

This is a story with four protagonists: a deadly bacterium, a vast city, and two gifted but very different men. One dark week a hundred fifty years ago, in the midst of great terror and human suffering, their lives collided on London’s Broad Street, on the western edge of Soho. This book is an attempt to tell the story of that collision in a way that does justice to the multiple scales of existence that helped bring it about: from the invisible kingdom of microscopic bacteria, to the tragedy and courage and camaraderie of individual lives, to the cultural realm of ideas and ideologies, all the way up to the sprawling metropolis of London itself. It is the story of a map that lies at the intersection of all those different vectors, a map created to help make sense of an experience that defied human understanding. It is also a case study in how change happens in human society, the turbulent way in which wrong or ineffectual ideas are overthrown by better ones. More than anything else, though, it is an argument for seeing that terrible week as one of the defining moments in the invention of modern life.

social outrage should be accompanied by a measure of wonder and respect: without any central planner coordinating their actions, without any education at all, this itinerant underclass managed to conjure up an entire system for processing and sorting the waste generated by two million people.

Without the bacteria-driven processes of decomposition, the earth would have been overrun by offal and carcasses eons ago, and the life-sustaining envelope of the earth’s atmosphere would be closer to the uninhabitable, acidic surface of Venus. If some rogue virus wiped out every single mammal on the planet, life on earth would proceed, largely unaffected by the loss. But if the bacteria disappeared overnight, all life on the planet would be extinguished within a matter of years.

Victorian London had its postcard wonders, to be sure—the Crystal Palace, Trafalgar Square, the new additions to Westminster Palace. But it also had wonders of a different order, no less remarkable: artificial ponds of raw sewage, dung heaps the size of houses.

Water closets were a tremendous breakthrough as far as quality of life was concerned, but they had a disastrous effect on the city’s sewage problem. Without a functioning sewer system to connect to, most WCs simply flushed their contents into existing cesspools, greatly increasing their tendency to overflow. According to one estimate, the average London household used 160 gallons of water a day in 1850. By 1856, thanks to the runaway success of the water closet, they were using 244 gallons.

here, they lower our dear brother down a foot or two: here, sow him in corruption, to be raised in corruption: an avenging ghost at many a sick-bedside: a shameful testimony to future ages, how civilization and barbarism walked this boastful island together.

No one died of stench in Victorian London. But tens of thousands died because the fear of stench blinded them to the true perils of the city, and drove them to implement a series of wrongheaded reforms that only made the crisis worse. Dickens and Engels were not alone; practically the entire medical and political establishment fell into the same deadly error: everyone from Florence Nightingale to the pioneering reformer Edwin Chadwick to the editors of The Lancet to Queen Victoria herself. The history of knowledge conventionally focuses on breakthrough ideas and conceptual leaps. But the blind spots on the map, the dark continents of error and prejudice, carry their own mystery as well. How could so many intelligent people be so grievously wrong for such an extended period of time? How could they ignore so much overwhelming evidence that contradicted their most basic theories? These questions, too, deserve their own discipline—the sociology of error.

By 1851, the subdistrict of Berwick Street on the west side of Soho was the most densely populated of all 135 subdistricts that made up Greater London, with 432 people to the acre. (Even with its skyscrapers, Manhattan today only houses around 100 per acre.) The parish of St. Luke’s in Soho had thirty houses per acre. In Kensington, by contrast, the number per acre was two.

“Mind you, the man who is in the minority of one is almost sure to be in the right.”

In terms of sheer numbers, bacteria are by far the most successful organisms on the planet. A square centimeter of your skin contains most likely around 100,000 separate bacterial cells; a bucket of topsoil would contain billions and billions. Some experts believe that despite their minuscule size (roughly one-millionth of a meter long), the domain of bacteria may be the largest form of life in terms of biomass.

an accidental ingestion of a million Vibrio cholerae can produce a trillion new bacteria over the course of three or four days. The organism effectively converts the human body into a factory for multiplying itself a millionfold. And if the factory doesn’t survive longer than a few days, so be it. There’s usually another one nearby to colonize.

Fertilization for all animals takes place in some form of water; embryos float in the womb; human blood has almost the same concentration of salts as seawater. “Those animal species that fully adapted to the land did so through the trick of taking their former environment with them,” the evolutionary biologist Lynn Margulis writes. “No animal has ever really completely left the watery microcosm…. No matter how high and dry the mountain top, no matter how secluded and modern the retreat, we sweat and cry what is basically seawater.”

For thousands of years, cholera was largely kept in check by these two factors: humans on the whole were disinclined to knowingly consume each other’s excrement; and, on those rare occasions when they did accidentally ingest human waste, the cycle wasn’t likely to happen again, thus keeping the bacteria from finding a tipping point where it spread at ever-increasing rates through the population, the way more easily transmitted diseases, like influenza or smallpox, famously do.

When Prince Albert first announced his idea for a Great Exhibition, his speech included these utopian lines: “We are living at a period of most wonderful transition, which tends rapidly to accomplish that great era to which, indeed, all history points: the realisation of the unity of mankind.” Mankind was no doubt becoming more unified, but the results were often far from wonderful. The sanitary conditions of Delhi could directly affect the conditions of London and Paris. It wasn’t just mankind that was being unified; it was also mankind’s small intestine.

Bacteria and viruses evolve at much faster rates than humans do, for several reasons. For one, bacterial life cycles are incredibly fast: a single bacterium can produce a million offspring in a matter of hours. Each new generation opens up new possibilities for genetic innovation, either by new combinations of existing genes or by random mutations. Human genetic change is several orders of magnitude slower; we have to go through a whole fifteen-year process of maturation before we can even think about passing our genes to a new generation.

The contagion theory had attracted some followers when the disease first reached British soil in the early 1830s. “We can only suppose the existence of a poison which progresses independently of the wind, of the soil, of all conditions of the air, and of the barrier of the sea,” The Lancet editorialized in 1831. “In short, one that makes mankind the chief agent for its dissemination.”

Remarkably, in all the discussion of cholera that had percolated through the popular and scientific press since the disease had arrived on British soil in 1832, almost no one suggested that the disease might be transmitted by means of contaminated water. Even the contagionists—who embraced the idea that the disease was transmitted from person to person—failed to see merit in the waterborne scenario.

the weakness of the contagionist argument. The same doctor attended both Harnold and Blenkinsopp, spending multiple hours in the room with them during the rice-water phase of the disease. And yet he remained free of the disease. Clearly, the cholera was not communicated through sheer proximity.

Snow embarked on a torrid stretch of inquiry: consulting with chemists who had studied the rice-water stools of cholera victims, mailing requests for information from the water and sewer authorities in Horsleydown, devouring accounts of the great epidemic of 1832. By the middle of 1849, he felt confident enough to go public with his theory. Cholera, Snow argued, was caused by some as-yet-unidentified agent that victims ingested, either through direct contact with the waste matter of other sufferers or, more likely, through drinking water that had been contaminated with that waste matter. Cholera was contagious, yes, but not in the way smallpox was contagious. Sanitary conditions were crucial to fighting the disease, but foul air had nothing to do with its transmission. Cholera wasn’t something you inhaled. It was something you swallowed.

Whitehead found himself musing on an old saying that invariably surfaced during plague times: “Whilst pestilence slays its thousands, fear slays its tens of thousands.” But if cowardice somehow made one more vulnerable to the ravages of the disease, Whitehead had seen no evidence of it. “The brave and the timid [were] indiscriminately dying and indiscriminately surviving,” he would later write.

mortality rates from 1842 had found that the average “gentleman” died at forty-five, while the average tradesman died in his mid-twenties. The laboring classes fared even worse: in Bethnal Green, the average life expectancy for the working poor was sixteen years. These numbers are so shockingly low because life was especially deadly for young children. The 1842 study found that 62 percent of all recorded deaths were of children under five.

Eventually, these first agricultural societies achieved what may still be the sine qua non of civilization: a large class of people liberated from the day-to-day problem of finding a new source of food. Cities were suddenly populated by a class of consumers, free to worry about other pressing matters: new technologies, new modes of commerce, politics, professional sports, celebrity gossip.

The Londoner enjoying a cup of tea with sugar in 1854 was drawing upon a vast global energy network with each sip: the human labor of the sugarcane plantations in the West Indies and the newly formed tea plantations in India; the solar energy in those tropical realms that allowed those plants to flourish; the oceanic energy of the trade currents, and the steam power of the railway engine; the fossil fuels powering the looms in Lancashire, making fabrics that helped fund the entire trade system.

In a sense, the Industrial Revolution would have never happened if two distinct forms of energy had not been separated from the earth: coal and commoners.

Brewed tea possesses several crucial antibacterial properties that help ward off waterborne diseases: the tannic acid released in the steeping process kills off those bacteria that haven’t already perished during the boiling of the water. The explosion of tea drinking in the late 1700s was, from the bacteria’s point of view, a microbial holocaust.

Do not mistake these multiple trends—the energy flows of metropolitan growth, the new taste for tea, the nascent, half-formed awareness of mass behavior—for mere historical background. The clash of microbe and man that played out on Broad Street for ten days in 1854 was itself partly a consequence of each of these trends, though the chains of cause and effect played out on different scales of experience, both temporal and spatial.

Once you get to why, the story has to widen and tighten at the same time: to the long durée of urban development, or the microscopic tight focus of bacterial life cycles. These are causes, too.

Viewed from space, the only recurring evidence of man’s presence on this planet are the cities we build. And in the night view of the planet, cities are the only thing going at all, geologic or biologic. (Think of those pulsing clusters of streetlights, arranged in the chaotic, but still recognizable patterns of real human settlement patterns, and not the clean, imperial geometry of political borders.)

Chadwick helped solidify, if not outright invent, an ensemble of categories that we now take for granted: that the state should directly engage in protecting the health and well-being of its citizens, particularly the poorest among them; that a centralized bureaucracy of experts can solve societal problems that free markets either exacerbate or ignore; that public-health issues often require massive state investment in infrastructure or prevention.

It’s true enough that the Victorians were grappling with heady issues like utilitarianism and class consciousness. But the finest minds of the era were also devoted to an equally pressing question: What are we going to do with all of this shit?

The first defining act of a modern, centralized public-health authority was to poison an entire urban population.

madness to celebrate the ever-increasing tonnage of human excrement being flushed into the water supply. And, indeed, it was a kind of madness, the madness that comes from being under the spell of a Theory. If all smell was disease, if London’s health crisis was entirely attributable to contaminated air, then any effort to rid the houses and streets of miasmatic vapors was worth the cost, even if it meant turning the Thames into a river of sewage.

Whenever smart people cling to an outlandishly incorrect idea despite substantial evidence to the contrary, something interesting is at work.

Just about every epidemic disease on record has been, at one point or another, attributed to poisoned miasma. The word “malaria” itself derives from the Italian mal aria, or “bad air.”

Whitehead had settled on what might later have been termed an ingeniously Darwinian explanation: that plagues were God’s way of adapting the human body to global changes in the atmosphere, killing off thousands or millions, but in the process creating generations that could thrive in the new environment.

Modern brain-imaging technology has revealed the intimate physiological connection between the olfactory system and the brain’s emotional centers. In fact, the seat of many of those emotional centers—the limbic system—was once called the “rhinencephalon,” literally “nose-brain” or “smell-brain.”

the human brain appears to have evolved an alert system whereby a certain class of extreme smells triggers an involuntary disgust response that effectively short-circuits one’s ability to think clearly—and produces a powerful desire to avoid objects associated with the smell.

There may be no clearer example of miasma’s dark irony: on the very day that the outbreak in Golden Square was beginning, one of London’s most prestigious papers was urging the Board of Health to accelerate its work poisoning the water supply.

obvious etiology: cholera was ingested, not inhaled.

Snow’s breakthroughs in anesthesia had revolved around his polymath skills as a physician, researcher, and inventor. But his cholera theory would ultimately depend on his skills as a sociologist.

However brilliant Snow was, he would never have proved his theory—and might well have failed to concoct it in the first place—without the population densities of industrial London, or Farr’s numerical rigor, or his own working-class upbringing. This is how great intellectual breakthroughs usually happen in practice. It is rarely the isolated genius having a eureka moment alone in the lab. Nor is it merely a question of building on precedent, of standing on the shoulders of giants, in Newton’s famous phrase. Great breakthroughs are closer to what happens in a flood plain: a dozen separate tributaries converge, and the rising waters lift the genius high enough that he or she can see around the conceptual obstructions of the age.

He drew maps in his head, looking for patterns, looking for clues.

the real innovation lay in the data that generated that diagram, and in the investigation that compiled the data in the first place. Snow’s Broad Street map was a bird’s eye view, but it was drawn from true street-level knowledge. The data that it sketched out in graphic form was a direct reflection of the ordinary lives of the ordinary people who made up the neighborhood. Any engineer could have crafted a dot map from William Farr’s Weekly Returns. But the Snow map drew on a deeper, more intimate, source: two Soho residents talking to their neighbors, walking the streets together, sharing information about their daily routines, and tracking down the long-departed émigrés. Neighborhood demographics had been projected onto maps before, of course, but invariably the projections involved the official interventions of the census takers or the Board of Health. Snow’s map—with Whitehead’s local knowledge animating it—was something else entirely: a neighborhood representing itself, turning its own patterns into a deeper truth by plotting them on a map. The map is a brilliant work of information design and epidemiology, no doubt. But it is also an emblem of a certain kind of community—the densely intertwined lives of a metropolitan neighborhood—an emblem that, paradoxically, was made possible by a savage attack on that community.

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.

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.

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.

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.

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.

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.