The Ghost Map: The Story of London’s Most Terrifying Epidemic—and How It Changed Science, Cities, and the Modern World
During the nineteenth century, Britain was struck by four epidemics of cholera, an often fatal disease characterized by attacks of diarrhea so intense that the body may lose gallons of water in just a few hours. The horrifying symptoms—dehydration so severe that the flesh shrinks back against the skull and the blood turns to jelly—appeared suddenly, and death could follow in the same day. It felt “like being hit with a club,” reported one survivor.1
Doctors, desperate to conceal their powerlessness, prescribed the following as “cures”: boiling water applied to the belly, electric shocks, enemas of turpentine and mutton stew, and gunpowder fired into the air in the vicinity of the patient. The public variously attributed the disease to ozone, ionic fields and other disturbances of the atmosphere, fumes produced by rotting sewage and putrescent yeast, and poison administered by doctors: at the time there was strong demand in medical schools for cadavers for dissection purposes, and this led to a spate of much-publicized murders, some of which were rumored to be linked to the cholera epidemics.2
Steven Johnson’s The Ghost Map tells the story of how the mystery of cholera transmission was solved by an ingenious physician named John Snow and how his discovery helped eliminate cholera from Britain and eventually from the Western world. But it also tells a parallel story about how a modern state bureaucracy emerged to confront one of the many novel challenges posed by urbanization. Nineteenth-century London was characterized by great civic turmoil. Never before had three million people lived together in so limited a space, and as Johnson points out, some doubted whether such a dense settlement was sustainable at all. Writer and publisher Sir Richard Phillips, whom Johnson quotes, even suggested there was something dangerous in the idea of the city itself:
The houses will become too numerous for the inhabitants, and certain districts will be occupied by beggary and vice or become depopulated. The disease will spread like an atrophy in the human body, and ruin will follow ruin, till the entire city is disgusting to the remnant of the inhabitants…. Such have been the causes of decay of all overgrown cities. Nineveh, Babylon, Antioch, and Thebes are become heaps of ruins….
The growth of cities and towns set off by the industrial revolution would forever transform the economy and culture of the West, but it also caused unprecedented upheavals, including vast inequalities in wealth, class tensions, the weakening of social ties, and overcrowding and squalor of an order previously unknown. These last conditions provided new niches for deadly diseases like cholera that could not spread through scattered rural populations.
Public coordination was required to manage a sprawling urban organism like London, and various government offices emerged to oversee the paving and lighting of streets, the collection of taxes, the construction and management of sewers, drains, prisons, and workhouses, and to respond to crises such as epidemics. Like the compartments of some giant developing brain, these offices were both crucial to the functioning of the creature of which they were a part, and also prone to mistakes.
One of the greatest challenges to urban life in the nineteenth century was the question of what to do with what Johnson calls the “rising tide of excrement” piling up under the feet of the population of London and other cities. At the time the custom was to throw one’s waste out the back window or store it in overflowing cesspools and cellars. An 1849 survey found that in London, one home in five stank of human waste, and one in twenty contained heaps of shit in the cellar. “At mid-century Victorian England was in danger of becoming submerged in a huge dung-heap of its own making,” wrote historian Anthony Wohl.3
The situation was alarming not only for the obvious reasons but also because the prevailing theory at the time held that diseases were caused not by germs but by “miasmas”—the bad smells emitted by sewage and rotting animal and vegetable matter. This idea, derived from ancient Greece, was seldom questioned. After all, the effect of disgusting smells on the appetite and digestion was well known, especially in the nineteenth century. “If we were to be transported back to a nineteenth-century town,” Wohl tells us, “it is probable that…we would be able to proceed only at risk of heaving stomach and nausea.” Thus when cholera, an ancient disease, spread west from its original breeding ground in South Asia during the 1820s and 1830s, it was immediately attributed to the clouds of miasma forming over Europe’s growing cities.
In 1842, the British social reformer Edwin Chadwick issued a report showing that the health of people living in towns was much worse than that of rural dwellers, and for the next twelve years, he dedicated himself to solving the problem of urban miasma. As head of the newly created General Board of Health, he launched a crusade to force reluctant taxpayers to fund the construction of an expanded sewer system that would clean out the cesspools and cellars of London. His efforts resulted in some progress, but unfortunately, the sewers he commissioned emptied right into the Thames River, which over the preceding decades had been “transformed from a fishing ground teeming with salmon to one of the most polluted waterways in the world,” even as much of the city’s drinking water continued to be drawn from it.
Since cholera germs normally spread by what epidemiologists call the “fecal-oral route,” Chadwick had thus inadvertently turned a pathway for their transmission into a superhighway. Some historians have deemphasized or even overlooked entirely the disastrous effects of this policy, arguing instead that Chadwick did the right thing (build sewers) for the wrong reason (to prevent disease by getting rid of smelly miasmas). Johnson emphasizes Chadwick’s mistake and shows that, as usual, bad science led to bad policy. It is likely that the severity of the cholera epidemics of 1848–1849 and 1854, which killed tens of thousands of people, was partly attributable to Chadwick’s sewers.
At around this time John Snow, an austere but ingenious London physician from a humble background in the north of England, produced a thirty-one-page monograph that explained cholera outbreaks once and for all. Or it would have, if it had been taken more seriously. Snow had encountered cholera during Britain’s first epidemic of 1831–1832, when he was working as an apothecary’s apprentice in Newcastle. He was struck by the pitiful squalor in which the victims lived, but he must have noticed that the disease didn’t always strike those who were most exposed to “miasmas.” For example, many of the “night soil men,” whose work brought them into very close contact with the most repulsive fumes, were spared.
The idea that cholera was transmitted through contaminated water had been suggested in medical circles from time to time, and when cholera struck again in 1848–1849, Snow observed that the only characteristic the victims seemed to share was access to a particular water source. It would be more than thirty years before Robert Koch identified the cholera bacterium under a microscope, and Snow’s insight, well described by Johnson, testifies to the power of the scientific imagination at its most creative.
Snow published his findings in the London Medical Gazette in 1849, but the medical community by and large dismissed them. It is not clear why, but many doctors, having devoted their careers to peddling the “cures” I have mentioned—mutton enemas and so on—based on the “miasma” theory might have been slow to entertain alternative ideas. Consciously or not, civic leaders may have been biased against the water-borne theory because of the huge expense involved in the implied remedy: a reliable system of sewers and pumps to remove human waste from the water supply. Moreover, Snow was an outsider; he hadn’t gone to Oxford or Cambridge and was awkward and shy when presenting his views in public. His findings relied on the techniques of the fledgling science of epidemiology—the measurement of disease in the messy real world rather than the controlled environment of a lab. Whatever the reason, the London Medical Gazette suggested one way in which Snow’s theory would stand or fall:
The experimentum crucis would be, that the water conveyed to a distant locality, where cholera had been hitherto unknown, produced the disease in all who used it, while those who did not use it, escaped.
This “crucial experiment” was soon made possible by the cholera epidemic of 1854. The outbreak struck South London first. When Snow went to investigate, he found that not every house was affected. By going door to door interviewing people, he was able to show that the stricken houses obtained water from a company that drew its supply directly from the filthiest part of the Thames. Those households that were spared obtained water from another company that drew from cleaner sources upstream. Snow then rushed to Soho, where another explosive outbreak was underway. There, he found that shortly before becoming ill, virtually every cholera victim had drunk water from the same pump, located on Broad Street. Very few people who did not drink Broad Street pump-water fell ill. Snow obtained permission from the Board of Health to remove the handle of the Broad Street pump, which, Johnson argues, may well have prevented another outbreak and saved many lives.
Months after the epidemic had passed, Snow drew a map showing the locations of the victims of the Soho outbreak. Today this map is one of the most famous documents in the history of science, but it made little impression at the time. Instead, the Board of Health produced a report of over one hundred pages focusing almost entirely on the quality of the air in London during the outbreak—wind speeds, ozone, and so on. Regarding Snow’s theory, the authors maintained, “We see no reason to adopt this belief.” When Snow died in 1858, his thirty-three-word obituary in The Lancet, which also had yet to embrace the germ theory, did not mention his contributions to the study of cholera at all.
But during the very summer of Snow’s death, opinion was beginning to turn in his direction. It was a particularly steamy and hot season and by June the Thames had become a putrescent stew. As its noxious contents floated past Parliament, the stench finally persuaded MPs that it was time—whatever the expense—to commission a vast system of sewers and pumps to transport London’s excrement far out of town. The completion of this system in 1867 was an occasion for national rejoicing and one sewage pumping station was even opened by the Prince of Wales. By now, news of Pasteur’s experiments with fermentation and the growing recognition that the miasma theory could not explain many of the facts about cholera had brought members of the medical community around to Snow’s point of view. Cholera would soon become a distant nightmare outside of the developing world.
Sandra Hempel, The Medical Detective: John Snow and the Mystery of Cholera (Granta, 2006), p. 3.↩
Hempel, The Medical Detective, pp. 36, 46–47, 52, 56, 78.↩
Anthony S. Wohl, Endangered Lives: Public Health in Victorian Britain (Harvard University Press, 1983), p. 86.↩