On Cross Street, not far from the Broad Street pump, there lived a tailor named Mr. G. Mr. G. and his son died early in the cholera epidemic of 1854, but their deaths became an important piece of the puzzle for John Snow.
Mr. G.’s death helped John Snow understand the relationship between a cause (consumption of water) and an effect (death from cholera).
After studying Farr’s latest figures, Snow came to realize that, while most of the cholera victims of 1854 had gotten their water from the Broad Street pump, and lived very close by, a few victims also lived on Cross Street—from which the Broad Street pump was slightly inconvenient to reach. Snow realized that he could use the Cross Street data to strengthen his theory and disprove miasma theory. But by the time Snow arrived at Cross Street to speak to Mr. G.’s surviving family, he learned that they were dead—“their late-night thirst for Broad Street water had destroyed them all.”
Snow knew that there had to be a connection between the consumption of water and contracting cholera; however, he was unable to get the information he needed because many of his subjects died before he could talk to them. While Snow’s waterborne theory seems obvious from a 21st-century perspective, Snow had to amass enough evidence to make his theory airtight—thus, the loss of more Soho locals to cholera was a devastating blow for his research, as well as a great human tragedy.
In following interviews, John Snow was able to determine that some of the other cholera victims living on Cross Street had gotten their water from the Broad Street pump. However, his sample size wasn’t big enough to be convincing—and there were two victims who had had no apparent connection to Broad Street. In order to make his case airtight, Snow needed to find examples of people who’d lived on Broad Street but hadn’t contracted cholera, because they hadn’t drunk from the Broad Street pump.
Snow’s research upheld one of the most basic scientific principles: a good theory should be falsifiable. By tracing the connection between the water pump and cholera, Snow didn’t merely strengthen his waterborne theory of cholera; he also developed a hypothesis that could be tested and proven false (i.e., if Broad Street locals who didn’t drink from the pump had died of cholera, then clearly Snow was mistaken in some way).
After more research, Snow discovered that not one of the Lion Brewery’s employees had died of cholera—quite possibly because these employees were paid partly in beer, and had a private water pipeline and well. In the nearby Eley Brothers factory, by contrast, dozens of employees had fallen ill—the Eley brothers had provided their workers with two large tubs of water, taken from the Broad Street pump. After learning that the brothers’ mother (Susannah Eley) had died, Snow discovered that they’d sent her some water from the pump.
Snow caught a lucky break (if “lucky” is an appropriate word for discussing a cholera epidemic) when he learned about the brewery and the Eley brothers’ mother—with this information, he strengthened the connection between the water pump and the cholera epidemic, eliminating many of the other confounding factors that had led other doctors to question the causational link between water and disease.
John Snow was a brilliant man, crusading against a medical establishment that believed in a false theory. But brilliance alone isn’t enough to explain why Snow didn’t buy miasma theory. In part, he had begun to question miasma after working with anesthetics. Snow’s entire career as an anesthesiologist was predicated on the assumption that vapors have a predictable, mechanistic effect on people who inhale them. He realized that ether, a miasma, was seemingly indifferent to the “inner constitution” of humans who inhaled it. He also decided that vapors emanating from excrement would be diffused through the air, to the point where they couldn’t do any damage. Snow further noticed that cholera attacked patients’ intestines first and foremost—if cholera was caused by vapors, wouldn’t it damage its victims’ respiratory systems?
Johnson resists the temptation to portray John Snow as a heroic crusader who fought for the waterborne theory of disease because he knew it was right. In reality, Snow, like any good scientist, was mostly looking for evidence to support his theory in order to convince himself, not just other scientists. Snow had some good reasons to believe that he was right about cholera (his experience as an anesthesiologist, for example), but these reasons didn’t add up to certainty—not even close. Rather, Snow’s life experiences and research gave him an advantage in seeing the issue of the cholera epidemic in a clear, unbiased manner.
It’s worth remembering that Snow lived less than six blocks from the outbreak of the cholera epidemic—suggesting that his interest in cholera was partly the result of pure geographic chance. Furthermore, Snow had a lot in common with the working-class victims of cholera in Soho; perhaps his own working-class background led him to treat his patients less prejudicially. In all, Snow’s resistance to miasma theory was “overdetermined” in the same way that miasma theory itself was overdetermined: it stemmed from small, almost unconscious factors, rather than a big, conscious decision.
In part, Snow was able to accumulate evidence in support of the germ theory of disease because of sheer random chance—had he been born in Paris or New York around the same time, it’s possible that he would never have gotten the opportunity to study cholera in such great detail, and miasma theory might have survived for another ten or twenty years. Johnson suggests that scientific progress—and, perhaps, progress in general—occurs because of a confluence of random factors, not simply because of the contributions of “great men” like John Snow.
As Henry Whitehead spent more time with cholera victims, he found himself growing increasingly furious with wealthy Victorians who claimed that the poor had “brought this on themselves.” When James Richardson, St. Luke’s scripture reader, failed to show up to church, Whitehead went to Richardson’s home and found his friend sick with cholera. The “inner constitution” explanation for disease was a lie, Whitehead was sure—Richardson was one of the strongest people he knew. Richardson mentioned to Whitehead that he’d drunk a glass of water from the Broad Street pump, and it occurred to Whitehead that the pump might have had something to do with the outbreak. Then, he decided this theory was silly—he’d had a glass of water himself, and he wasn’t sick.
Henry Whitehead was unlike John Snow in many ways, but they had some things in common—in particular, their lack of patience for conventional dogma and prejudice. Whitehead and Snow were uncommonly clear-eyed thinkers—however, Whitehead had a hard time believing in the waterborne theory because he didn’t have all the information (nor, for that matter, did Snow). Whitehead had no way of knowing that the glass of brandy had saved his life the previous evening, killing the cholera bacteria in the water.
It’s not clear what was happening in the well below Broad Street. By Wednesday, fewer people were contracting cholera, suggesting that cholera bacteria were dying. Perhaps the bacteria were victims of their own success. In other words, the fact that the cholera outbreak took place in a dense neighborhood meant that the bacteria could spread like wildfire—but the epidemic killed off so many people that the remaining bacteria had fewer hosts to infect. It’s also possible that the bacteria had been starving in the cold, dark water beneath the pump.
Johnson has to admit that it’s still not clear why the cholera epidemic ended when it did. In retrospect, readers have no problem seeing how the 1854 epidemic verifies the germ theory of disease—at the time, however, the sudden end of the epidemic posed a significant challenge to Snow’s research, and made other doctors question whether or not cholera was a contagious agent.
As Whitehead visited other sick and recovering cholera victims, he found that many people said they’d begun to recover from their illness after drinking water from the Broad Street pump. However, many other people who’d drunk from the pump earlier in the week weren’t available for discussion—since they were dead. It is possible that the cholera bacteria in the pump had died off, or perhaps the flow of groundwater had cleansed the pump supply.
This passage suggests how cholera epidemics “resolved” themselves before the era of germ theory —either the epidemic killed so many human beings that it lost its ability to grow exponentially, or natural factors swept away the germs that had launched the epidemic.
By the end of the day, John Snow had built a strong case against the Broad Street pump: the vast majority of deaths Farr had recorded had occurred in houses for which the Broad Street pump was the nearest available water source, and of that group, the majority consisted of habitual pump drinkers. There were six victims Snow couldn’t account for, however—they didn’t appear to drink from the pump at all. But Snow had also learned that there was a coffeehouse owner who sold sherbet mixed with Broad Street water—and many of her patrons had died. In a single day, Snow had interviewed dozens of people and strengthened his contagion theory. It’s even possible that Snow’s vigorous questioning of Soho locals curbed the spread of the disease, since some of his questions made the locals question their own behavior regarding the well.
Snow reviewed the evidence and concluded that he had a strong case for a waterborne theory. The theory was “strong” because it not only explained why certain people contracted cholera; it also explained why other people (such as the brewery employees) didn’t contract it. The passage also shows Snow inadvertently influencing people’s behavior in the act of trying to study it—i.e., by asking questions about the water pump, he probably convinced some of his interviewees to be suspicious of drinking from the pump.
Although the epidemic may have been in decline, it was still killing people. A dozen people died in Soho that day—ten times the normal rate. Snow prepared to finalize and publish his research, but before he did so, there was “a more pressing matter”—removing the actual culprit for the outbreak.
Snow was about to embark on the most revolutionary phase of his investigation—translating medical research into public policy, something that had rarely been done before (at least not when the medical research in question was scientifically sound).