On Sunday, September 3, Soho had become eerily calm. Few people went to get water from the Broad Street pump—most of the people walking the streets that morning were doctors and priests. News of the outbreak had reached the rest of London—there had been cholera outbreaks before, but none so deadly.
One of the eeriest things about the 1854 cholera epidemic was that it traveled faster than the news—by the time the rest of London heard about it, it had already eliminated a sizeable portion of Soho’s population.
On Sunday, a forty-two year-old Soho regular named John Snow was walking through the streets. Snow’s father was a Yorkshire laborer. When the young Snow showed signs of brilliance, his father arranged for him to work for a Newcastle surgeon, where he witnessed the ravages of cholera. In the 1830s, Snow was a prominent member of the temperance (i.e., anti-alcohol) movement; at twenty-three, however, he decided to study medicine in London. Snow quickly proved to be a superb doctor, quick-witted and calm under pressure. In the 1840s, he’d published dozens of articles. By 1843 he’d earned his M.D. from the University of London, and within a year he’d passed his exams and become a doctor.
Here, we’re introduced to John Snow—the closest thing to a protagonist in the book. Snow was a fascinating figure, in particular because of his ambition and curiosity about the world. Snow had to work hard to go to medical school, and he kept up the same work ethic even after he graduated. It’s ironic that Snow promoted temperance, considering that the consumption of alcohol saved the lives of dozens of people during the cholera epidemic of 1854, which he later studied.
Most doctors in Snow’s position would have settled into a comfortable, upper-middle-class life. However, Snow remained ambitious—in particular, he wanted to study pain management. At the time, Western medicine had only two reliable forms of anesthesia: alcohol and opium. Surgeries were torturous for patients, and surgeons prided themselves on being fast, rather than careful. In the fall of 1846, however, the Boston dentist William Morris gave the first public demonstration of etherized anesthesia, and by the end of the year, the use of ether had spread to London. However, the first doctors to use ether were clumsy—sometimes, they used so much of it that their patients never woke up.
Snow’s curiosity was boundless—based on his career, he seemed to enjoy the thrill of learning about a new field of medicine more than the financial perks of being a highly sought-after doctor. The use of anesthesia is so uncontroversial in 21st century medicine that it’s striking to think that, just 150 years ago, doctors had virtually no way of controlling their patients’ pain, and had to sacrifice accuracy and care just to shorten their procedures.
Snow devoted himself to determining correct ether dosages. By January 1847, he’d published a table of correct dosages; he also designed an ether inhaler device. When Snow discovered that chloroform was often a better anesthetic than ether, he became London’s most sought-after anesthesiologist. Snow wasn’t just a fast worker and a quick thinker; he was also a world-class “consilient thinker.” In other words, his thinking bridged different disciplines, including chemistry, biology, and mechanics.
It’s incredible that, just a few months after Morris’s demonstration, Snow had already developed a sophisticated method of controlling the flow of ether. The principle of consilience isn’t just a good way to understand the way Snow’s mind worked—it’s a good way of describing The Ghost Map itself, as Johnson synthesizes several disciplines, including philosophy, history, futurology, epidemiology, microbiology, literature, and urban planning.
By the end of the 1840s, John Snow had become fascinated with cholera. There was a cholera outbreak in 1848, and Snow wanted to determine the cause. Some doctors believed in the “contagion theory”—that cholera was caused by an “agent” that passed between its victims. Others advocated the “miasma theory”—that cholera was caused by unsanitary spaces and bad odors. At the time, miasma theory was far more popular with medical insiders, including the London sanitation commissioner and London’s chief demographer, William Farr. Few argued that cholera was spread by contaminated water.
Snow, as it turned out, believed the correct theory of cholera—that it was spread by a material agent (which doctors later determined to be bacteria) rather than emanating, vapor-like, from certain environments. Notice, however, that Snow was far from certain of his theory—he didn’t even know what the precise agent of cholera was, and therefore couldn’t be sure of his contagion theory.
In the course of his research, Snow found reports of a Hamburg steamship, one of whose crew members checked into a lodging house and later died of cholera. An Englishman who later stayed in the lodging house also contracted cholera, and the disease then spread around the neighborhood. The evidence could have supported the miasma model, except that it would have been a wild coincidence if the lodging house became a noxious environment on the exact day when a sailor from Hamburg—then experiencing its own cholera epidemic—arrived.
Although Snow didn’t know what the “agent’ of cholera was, he studied the evidence and realized that cholera must be caused by an agent of some kind. If miasma theorists were correct, then one would have to believe that the sailor’s lodgings became noxious overnight—a pretty big assumption. (It’s interesting to consider how few cases of cholera passing from a person of one nationality to another—cases which clearly supported contagion theory—there were in the 1850s: 19th century Europe was certainly not as globalized as the present.)
By 1849, Snow was ready to present his research to the public: cholera, he argued, was caused by an agent that its victims ingested, either through contact with waste matter or ingestion of contaminated water. Snow strengthened his theory after an outbreak of cholera in Horsleydown; all the evidence pointed to the disease spreading aquatically. Snow also studied William Farr’s data and maps on the spread of cholera. He found that cholera deaths correlated closely with certain shared water supplies. He further found that there was little correlation between squalid conditions and cholera outbreaks—sometimes, one slum building would be full of cholera victims while the one next door would be cholera-free. Other doctors were appreciative but skeptical of Snow’s argument; even if Snow had established a correlation between water supply and disease, they argued, he hadn’t confirmed the cause of the epidemic.
In retrospect, it seems utterly obvious that John Snow was correct about the causes of cholera—but at the time, his evidence seemed anything but conclusive. Snow could show a strong correlation between water supply and cholera outbreaks, but because he had no idea what the contagious agent of cholera was (in the 1840s, nobody did), his theory was much weaker than it seems in retrospect. At the time, miasma theory—in which the only “agent” was smell—seemed a much more tangible, intuitively believable theory than contagion theory (which was only proven true after scientists identified microbial cells in the 1850s and 1860s).
In 1854, with the cholera outbreak, Snow began to study Soho’s water supply. He was surprised to find that the water looked normal—it wasn’t even cloudy. Meanwhile, Susannah Eley, the mother of the Eley Brothers, had fallen ill after drinking water from the Broad Street pump, which the Eley Brothers had shipped specially to Hempstead for her.
Snow had access to Soho’s water supply but he didn’t have a good way of studying water samples. Victorian scientists had access to microscopes (which had been around since the 1700s), but it took decades before the germ theory of disease was universally accepted.
Whitehead spent September 3, 1854 walking through the streets of Soho, alarmed by how empty the neighborhood had become. When he came home, he contemplated the rumors that people living in rooms on the upper floors of Soho’s buildings were more likely to die than those living on the ground floor. This information appealed to London society’s strong class bias—at the time, ground floor rooms were more hotly desired than rooms on the upper floor. But as he considered the matter, Whitehead realized the truth: more upper floor residents people were dying because more people lived on upper floors.
The book parallels Snow’s investigations into cholera with those of Henry Whitehead. While Whitehead lacked Snow’s scientific genius, he was singularly devoted to his neighbors and friends, and used pure common sense to see through the medical obscurantism of the time. In a way, Whitehead is a lot like the ideal reader of The Ghost Map: he lacks any particular medical knowledge, but he has enough common sense to understand the nature of the epidemic.
The very same evening, John Snow was looking over the mortality numbers for the 1854 outbreak compiled by William Farr. Snow and Whitehead had one thing in common that evening: they were both sitting in their rooms with glasses of water pumped from Broad Street. Snow examined his glass, suspicious that it contained the mysterious cholera agent. Whitehead, however, mixed his water with brandy and drank it.
One reason that Whitehead was skeptical of contagion theory was that he’d drunk from the Broad Street pump himself, and survived. 21st-century readers will recognize why: brandy is sterile, and actually kills bacteria, so the water Whitehead was drinking no longer contained living cholera.