The Ghost Map: The Story of London's Most Terrifying Epidemic--and How It Changed Sci

"The probability of an outburst or increase during [calm, mild] weather, I believed to be heightened on holidays, Saturdays, Sundays, and any other occasions where opportunities were afforded the lower classes for dissipation and debauchery" - unattributed quote by ‘expert' regarding how cholera disproportionally attacks the poor and other social underclasses, in Victorian London.

As strange as this seems to modern eyes, this statement was backed up by scientific evidence, or at least what passed for such in England of the mid-19th century. During this time, the predominant theory for the spread of contagion and sickness was miasma (Greek for "pollution"), that is bad smells and foul air were the causes of disease.

The Ghost Map: the Story of London's Most Terrifying Epidemic - and How it Changed Science, Cities, and the Modern World, by Steven Johnson (Riverhead Books) is the story of Dr. John Snow and Rev. Henry Whitehead's discovery of the water-born transmission of cholera, a disease which struck with terrifying regularity in London and other large cities. The popular folklore is that Dr. Snow plotted cases of cholera deaths on a map, and deduced that the outbreak's source was a particular well in a poor section of London, and removed the handle to the pump, thereby halting the epidemic, and was hailed as a hero.

The true story is not nearly so neatly packaged. Dr. Snow noticed, in earlier epidemics, a pattern of isolated groups either contracting cholera in isolation, or seeing groups that were spared contagion in the middle of a raging epidemic. Using his skills and experience, he correctly deduced that water somehow carried the source of the disease (although he had no idea about germ theory), and managed to track the common source to the water well located on Broad Street, in the area now known as Soho. Although he was unable to find anything in the water that could be the source of the disease (in fact, other wells had cloudy or smelly water, but no pattern of contagion). Over a period of months, however, he was unable to convince the health boards and community groups of his findings, because it was commonly known that bad smells were the source of disease, and indeed this had been known for centuries. This belief was continually reinforced because the most stricken areas, such as Broad Street, also happened to be the dirtiest and most fetid location in London. The scientists of the day could confirm their views by taking an (admittedly short) stroll through the impacted areas.

London grew from a city of a few hundred thousand to over 2 million in a matter of decades. Before the growth, most human waste was collected and carried to the surrounding farmland for fertilizer. However, with the rapid grow and expansion of the city limits, the feasibility and cost to remove ‘night soil' became too expensive for the poor, and so the waste collected in the cesspools under the houses and in open pits in the alleys and yards. What few sewage systems existed dumped the untreated water directly into the Thames. The invention of the water closet increased the problem, since the additional water used for flushing ended up in the same overflowing pits. London was drowning in human waste, and it was commonly believed that the city would eventually perish under its mountain of refuse. And, common ‘scientific' belief was that since the worst situation, and the worst smells, existed in the poorest neighborhoods, as did the greatest incidences of disease, crime, and death, the poor somehow brought it upon themselves, hence the quotation at the beginning of this article.

Dr. Snow eventually persuaded the local council to remove the pump handle, but by this time, new cases of cholera (and the original index source of the outbreak) had moved on. The councils were not, however, persuaded of the invalidity of their belief in miasma. In fact, Dr. Snow's views were openly mocked on the pages of The Lancet and the newspapers of the day. How did they explain that in some cases, some members of a family died while other survived, while supposedly breathing the same foul air? Or that one household might entirely succumb while their immediate neighbors, who shared a yard, might all survive? The Victorians concluded, based on their understanding of the evidence, was that a person's inherent constitution and moral character could be protective. Reverend Whitehead, who served as the local vicar and knew nearly all of the people of the Broad Street area on a first-name basis, initially scoffed at Dr. Snow's hypothesis, as well, but became intrigued and finally assisted Dr. Snow's data collection efforts when he realized that the ‘constitution and moral character' of the individuals succumbing to cholera did not necessarily jive with the mortality cases. He also helped Dr. Snow track down and tabulated cases of cholera among ‘the better sort' of people who no longer lived in the Broad Street area but may have partaken of the well's water during a visit. He was also impressed that the entire population of a workhouse (the Victorians' favorite scapegoat) survived the outbreak, as did all of the workers at a particular brewery, who were paid in product and never drank water.

In the end, it was not an epiphany that led Dr. Snow to his breakthrough, but years of plodding, shoe leather, tedious tabulation of victims, and his now-famous map, that convinced the skeptics of his claim. It was nearly 10 years after the outbreak before Dr. Snow's discovery was finally accepted by mainstream scientists and politicians, and it was shortly after that that London finally embarked on the ambitious plan to install both sewer collection systems and to supply filtered water to the population of London. The last cholera outbreak was in 1866, shortly before the completion of the system. London's example served as a model for the other great cities of the world.

Dr. Snow and Rev. Whitehead's true legacies are not that they stopped cholera epidemics, but that they introduced a multidisciplinary approach in thinking about medical and scientific problems, and modernized the methods of scientific inquiry.