Hippocrates mentioned cholera as a common post-childhood disease, but given that he thought it might be brought on by eating goat’s meat he was probably referring to a less malign form of diarrhea. It was almost certainly not the life-threatening epidemic disease that emerged from India in 1817 and which then began its spread around the world, travelling, as Snow said, “along the great tracks of human intercourse”—colonialism and global trade. The first pandemic of what the British and the Americans called Asiatic cholera (or cholera morbus) reached Southeast Asia, East Africa, the Middle East, and the Caucasus, but petered out in 1823. A second pandemic, between 1826 and 1837, also originated in India, but this time it took a devastating toll on both Europe and America, arriving in Britain in the autumn of 1831 and in America the following year. By 1833, twenty thousand people had died of cholera in England and Wales, with London especially hard hit. A third pandemic swept England and Wales in 1848-49 (more than fifty thousand dead) and again in 1854, when thirty thousand died in London alone.
Cholera is a horrific illness. The onset of the disease is typically quick and spectacular; you can be healthy one moment and dead within hours. The disease, left untreated, has a fatality rate that can reach fifty per cent. The first sign that you have it is a sudden and explosive watery diarrhea, classically described as “rice-water stool,” resembling the water in which rice has been rinsed and sometimes having a fishy smell. White specks floating in the stool are bits of lining from the small intestine. As a result of water loss—vomiting often accompanies diarrhea, and as much as a litre of water may be lost per hour—your eyes become sunken; your body is racked with agonizing cramps; the skin becomes leathery; lips and face turn blue; blood pressure drops; heartbeat becomes irregular; the amount of oxygen reaching your cells diminishes. Once you enter hypovolemic shock, death can follow within minutes. A mid-nineteenth-century English newspaper report described cholera victims who were “one minute warm, palpitating, human organisms—the next a sort of galvanized corpse, with icy breath, stopped pulse, and blood congealed—blue, shrivelled up, convulsed.” Through it all, and until the very last stages, is the added horror of full consciousness. You are aware of what’s happening: “the mind within remains untouched and clear,—shining strangely through the glazed eyes . . . a spirit, looking out in terror from a corpse.”
The fact that the poor suffered most in many epidemics was readily accommodated by the miasmal theory: certain people—those who lived in areas where the atmosphere was manifestly contaminated and who led a filthy and unwholesome way of life—were “predisposed” to be afflicted. The key indicator of miasma was stench. An aphorism of the nineteenth-century English sanitary reformer Edwin Chadwick was “All smell is disease.” Sydenham’s belief in a subterranean origin of miasmas gradually gave way to the view that they were caused by the accumulation of putrefying organic materials—a matter of human responsibility. As Charles E. Rosenberg’s hugely influential work “The Cholera Years” (1962) noted, when Asiatic cholera first made its appearance in the United States, in 1832, “Medical opinion was unanimous in agreeing that the intemperate, the imprudent, the filthy were particularly vulnerable.” During an early outbreak in the notorious Five Points neighborhood of Manhattan, a local newspaper maintained that this was an area inhabited by the most wretched specimens of humanity: “Be the air pure from Heaven, their breath would contaminate it, and infect it with disease.” The map of cholera seemed so intimately molded to the moral order that, as Rosenberg put it, “to die of cholera was to die in suspicious circumstances.” Rather like syphilis, it was taken as a sign that you had lived in a way you ought not to have lived. “The great mass of people . . . don’t know that the miasma of an unscavenged street or impure alley is productive of cholera and disease,” the English liberal economic activist Richard Cobden observed in 1853. “If they did know these things, people would take care that they inhabited better houses.”
Élite presumptions to the contrary, the London poor did not enjoy living in squalor. In 1849, a group of them wrote a joint letter to the London Times:
"We live in muck and filthe. We aint got no priviz, no dust bins, no drains, no water-splies . . . . The Stenche of a Gully-hole is disgustin. We all of us suffer, and numbers are ill, and if the Colera comes Lord help us. . . . We are livin like piggs, and it aint faire we shoulde be so ill treted. "
But some sanitary reformers, Florence Nightingale among them, opposed contagionism precisely because they believed that the poor were personally responsible for their filth: contagionism undermined your ability to hold people to account for their unwholesome way of life. Whereas, in a miasmal view of the world, the distribution of disease followed the contours of morality—your nose just knew it—infection by an external agent smacked of moral randomness.
Why was it, he wondered, that people most exposed to these supposedly noxious miasmas—sewer workers, for example—were no more likely to be afflicted with cholera than anyone else? Snow also knew that the concentration of gases declined rapidly over distance, so how could a miasma arising from one source pollute the atmosphere of a whole neighborhood, or even a city? Why, if many of those closest to the stench were unaffected, did some of those far removed from it become ill? And there were some notable outbreaks of cholera that didn’t appear to fit with the moral and evidential underpinnings of miasmal theory. Sometimes the occupants of one building fell ill while those in an adjacent building, at least as squalid, escaped. Moreover, cholera attacked the alimentary, not the respiratory, tract. Why should that be, if the vehicle of contagion was in the air as opposed to something ingested?
From medieval times, water had been drawn both from urban wells and from the Thames and its tributaries. In the early seventeenth century, the so-called New River was constructed; it carried Hertfordshire spring water, by gravity alone, to Clerkenwell, a distance of almost forty miles. During the eighteenth century and the early nineteenth, a number of private water companies were established, taking water from the Thames and using newly invented steam pumps to deliver it by iron pipe. By the middle of the nineteenth century, there were about ten companies supplying London’s water. Many of these companies drew their water from within the Thames’s tidal section, where the city’s sewage was also dumped, thus providing customers with excrement-contaminated drinking water. In the early eighteen-fifties, Parliament had ordered the water companies to shift their intake pipes above the tideway by August of 1855: some complied quickly; others dragged their feet.
When cholera returned, in 1854, Snow was able to identify a number of small districts served by two water companies, one still supplying a fecal cocktail and one that had moved its intake pipes to Thames Ditton, above the tidal section. Snow compiled tables showing a strong connection in these districts between cholera mortality and water source. Snow’s “grand experiment” was supposed to be decisive: there were no pertinent variables distinguishing the two populations other than the origins of their drinking water. As it turned out, the critical evidence came not from this study of commercially piped river water but from a fine-grained map showing the roles of different wells. Snow lived on Sackville Street, just around the corner from the Royal Academy of Arts, and in late August cholera erupted practically next door, in an area of Soho. It was, Snow later wrote, “the most terrible outbreak of cholera which ever occurred in this kingdom”—more than five hundred deaths in ten days.
Using the Weekly Return of Births and Deaths, which was published by William Farr, a statistician in the Office of the Registrar-General, and a staunch anti-contagionist, Snow homed in on the microstructure of the epidemic. He began to suspect contaminated water in a well on Broad Street whose pump served households in about a two-block radius. The well had nothing to do with commercially piped water—which in this neighborhood happened to be relatively pure—but it was suspicious nonetheless. Scientists at the time knew no more about the invisible constituents of the water supply than they did about the attributes of specific miasmas—Snow wrote that the “morbid poison” of cholera “must necessarily have some sort of structure, most likely that of a cell,” but he could not see anything that looked relevant under the microscope—so even Snow still used smell as an important diagnostic sign. He recorded a local impression that, at the height of the outbreak, the Broad Street well water had an atypically “offensive smell,” and that those who were deterred by it from drinking the water did not fall ill. What Snow needed was not the biological or chemical identity of the “morbid poison,” or formal proof of causation, but a powerful rhetoric of persuasion. The map Snow produced, in 1854, plotted cholera mortality house by house in the affected area, with bars at each address that showed the number of dead. The closer you lived to the Broad Street pump, the higher the pile of bars. A few streets away, around the pump at the top of Carnaby Street, there were scarcely any bars, and slightly farther, near the Warwick Street pump, there were none at all.
Snow’s study of the neighborhood enabled him to add persuasive anecdotal evidence to the anonymity of statistics. Just across from the Broad Street pump was the Poland Street workhouse, whose wretched inmates, living closely packed in miserable conditions, should have been ideal cholera victims. Yet the disease scarcely touched them. The workhouse, it emerged, had its own well and a piped supply from a company with uncontaminated Thames water. Similarly, there were no cholera deaths among the seventy workers in the Lion Brewery, on Broad Street. They drank mainly malt liquor, and the brewery had its own well. What Snow called the “most conclusive” evidence concerned a widow living far away, in salubrious Hampstead, and her niece, who lived in “a high and healthy part of Islington”: neither had gone anywhere near Broad Street, and both succumbed to cholera within days of its Soho outbreak. It turned out that the widow used to live in the affected area, and had developed a taste for the Broad Street well water. She had secured a supply on August 31st, and, when her niece visited, both drank from the same deadly bottle.
Next, Snow had to show how the Broad Street well had got infected, and for this he made use of the detailed knowledge of a local minister, Henry Whitehead. The minister had at first been skeptical of Snow’s waterborne theories, but became convinced by the evidence the doctor was gathering. Whitehead discovered that the first, or “index,” case of the Soho cholera was a child living on Broad Street: her diapers had been rinsed in water that was then tipped into a cesspool in front of a house just a few feet away from the well. The cesspool leaked and so, apparently, did the well. Snow persuaded the parish Board of Guardians to remove the handle from the Broad Street pump, pretty much ending the Soho cholera outbreak. There’s now a replica of the handleless pump outside a nearby pub named in John Snow’s honor.
In the oppressively hot summer of 1858, London was overwhelmed by what the papers called “the Great Stink.” The already sewage-loaded Thames had begun to carry the additional burden of thousands of newly invented flush water closets, and improved domestic sanitation was producing the paradoxical result of worsened public sanitation. The Thames had often reeked before, but this time politicians fled the Houses of Parliament, on the river’s embankment, or attended with handkerchiefs pressed to their noses. “Whoso once inhales the stink can never forget it,” a newspaper reported, “and can count himself lucky if he live to remember it.” Measures to clean up the Thames had been on the agenda for some years, but an urgent fear of miasmas broke a political logjam, and gave immediate impetus to one of the great monuments of Victorian civil engineering: Sir Joseph Bazalgette’s system of municipal sewers, designed to deposit London’s waste below the city and far from the intakes of its water supply. (The system became fully operational in the mid-eighteen-seventies, and its pipes and pumps continue to serve London today.)
In the event, the Great Stink’s effects on municipal health were negligible: the Weekly Return showed no increase in deaths from epidemic disease, confounding miasmatists’ expectations. When cholera returned to London in 1866, its toll was much smaller, and the main outbreak was traced to a section of Bazalgette’s system which had yet to be completed. In many people’s opinion, Snow, who had died in 1858, now stood vindicated. And yet the improved municipal water system that rid the city of cholera had been promoted by sanitary reformers who held to the miasmal theory of disease—people who believed that sewage-laden drinking water was only a minor source of miasmas, but disgusting all the same. The right things were done, but not necessarily for the right scientific reasons.