The Ghost Map


Steven Johnson

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In the 1850s, London was the largest city in Europe, and one of the filthiest cities in the world. At a time when the majority of the world lived in rural communities, in London millions of people lived within a few miles of each other—and the city lacked a sanitation system that could deal with millions of people’s garbage and waste. The sewers were often clogged with waste, and “night-soil men” made good money cleaning up excrement at night and dumping it at the edges of the city.

In 1854, a child became violently ill; the mother, Sarah Lewis, threw the baby’s soiled diapers in a cesspool in the basement of her home. Soon afterwards, there was a cholera epidemic in the London neighborhood of Soho. Within a few days, dozens of people had become seriously ill. Cholera is a bacterial, waterborne disease that has existed for thousands of years, although it’s only become a major killer in the modern, urban era (in ancient times, most communities weren’t dense enough to facilitate the spread of the disease). When it infects a human being, cholera targets the small intestine, causing dehydration, vomiting, and diarrhea. The simplest cure for cholera is a combination of clean water and electrolytes. However, in communities without access to clean water, such as Victorian London, cholera posed a major threat.

During the 1854 epidemic, there was a priest named Henry Whitehead living near Soho. Whitehead knew almost all the families living in the neighborhood, and he traveled from house to house, speaking to the families of cholera victims.

Another important figure in the 1854 epidemic was a young doctor named John Snow. Snow had already made a name for himself as a pioneering anesthesiologist; however, he’d become interested in cholera epidemics after an outbreak of the disease in 1848. At the time, there were two dominant theories for how cholera spread—the contagion theory (that some kind of agent passed between cholera victims) and the miasma theory (that bad odors, emanating from certain environments, caused cholera, especially in people who had certain “internal constitutions”). Snow had assembled convincing evidence supporting contagion theory, and he believed that the 1854 epidemic could further strengthen his case.

Snow’s conundrum was that the medical community of the mid-1800s was dead-set on miasma theory. The founder of London’s influential General Board of Health, Edwin Chadwick, was a steadfast supporter of the theory. Miasma theory catered to human beings’ natural instinct to associate sickness with bad smells, and it may have appealed to certain class biases in Victorian society (e.g., that poor people deserved their sickness). Chadwick’s commitment to miasma theory—and his blindness to the truth about how diseases spread—led him to propose the unclogging of the existing sewer system, resulting in millions of pounds of added filth in the river Thames, which almost certainly triggered epidemics throughout the 1850s.

As the 1854 cholera epidemic continued, Snow and Whitehead each visited dozens of households in Soho and interviewed the residents in order to learn more about cholera. Snow began to realize the truth: the disease was being spread through the Broad Street water pump, the main source of “clean” water for most of the community. Snow became surer of his theory after speaking with William Farr, a prominent demographer who’d been collecting data about recent cholera epidemics. Snow also used the data to develop refutations to the popular miasma theory—for example, if bad odors spread diseases, then why had some buildings in the Soho neighborhood been almost completely spared from cholera?

Snow spoke at an emergency meeting of the board of governors at St. James’s Parish, and urged the governors to remove the pump handle from the Broad Street well. With some reluctance, the board agreed to do so. Though the epidemic had already been dying down, Snow’s actions probably prevented the epidemic from continuing any further.

A few months later, the president of the General Board of Health, Sir Benjamin Hall, announced a committee to investigate the causes of the epidemic. However, because Hall was a firm believer in miasma theory, his investigation studied the wrong factors and led to few strong conclusions. Around the same time, St. James Vestry hired Henry Whitehead to lead a committee into the causes of the epidemic. Whitehead had been opposed to Snow’s argument that the pump handle be removed. He’d learned from interviewing local families that many of the people who’d recovered from cholera attributed their recoveries to drinking water from the Broad Street well. However, in the course of his investigation, Whitehead found himself coming around to Snow’s point of view. He realized that the Lewis family had thrown soiled diapers into a cesspool which had contaminated the well, probably causing the outbreak of cholera in the community.

Around the same time, John Snow further strengthened his waterborne cholera theory. He determined that two Soho locals had sent their mother a glass of water from the Broad Street pump, and then been shocked to learn that their mother had died of cholera. He also found that Soho locals who didn’t drink from the pump hadn’t been afflicted with cholera. Whitehead became one of Snow’s foremost advocates. However, miasma theory continued to dominate the medical community.

Snow and Whitehead’s investigation into the cholera epidemic of 1854 marked a milestone in urban history: it probably represented one of the first occasions on which a municipal group had come together to make a decision for public health, based on good science and research. Snow’s research set a strong precedent for the role of medicine in urban planning—indeed, in the years following the outbreak, Snow’s waterborne theory became increasingly well-accepted, to the point where all European and American cities planned their sewer systems with the assumption that diseases were contagious and carried via water. Although Snow died young, long before his theories became universally accepted, his achievements arguably made possible the growth of urban populations: Western cities largely ceased to be centers of disease and filth.

In the Epilogue, Johnson discusses the future of urbanism. For the last 150 years, an increasingly high percentage of the human race has come to live in urban areas, and it seems likely that this process will continue. Two factors that may limit the unchecked growth of cities are epidemics and terrorist attacks. In cities, epidemics spread at an exponential rate—that’s why cholera killed so many people in London in 1854. And cities are practically bull’s-eyes for terrorists, since so many people live so close together. If human beings are to continue living in cities, they’ll have to find ways to apply their ingenuity and hard work to addressing these dangers—and they would do well to take after Henry Whitehead and John Snow.