Source: Old News 16(8), 8-10, May & June, 2005.

 "For his persistent efforts to determine how cholera was spread and for the statistical mapping methods he initiated, John Snow is widely considered to be the father of [modern] epidemiology."


Doctor John Snow Blames Water Pollution for Cholera Epidemic

by David Vachon

John Snow, born in 1813, was the son of a coal-yard laborer in York, England. As a boy he proved to be an exceptionally bright, methodical, and eager student, so his mother used a small inheritance to send him to a private school, where he excelled.

Snow planned to become a physician, and at fourteen, he was apprenticed to Dr. William Hardcastle in Newcastle- upon-Tyne (center right). Snow had an analytical mind that thrived on details that others often overlooked. During his early years as an apprentice, he filled notebooks with his thoughts and observations on scientific subjects.

Dr. John Snow in the mid-1850s

In the summer of 1831, when Snow was eighteen and in his fourth year as an apprentice, an epidemic of cholera struck London. The disease, which had already killed hundreds of thousands of people on the European continent, spread north to Newcastle in October. The first symptom of cholera was queasiness, followed by stomachache, vomiting, and diarrhea so profuse that it caused victims to die of dehydration.

Dr. Hardcastle had so many sick patients that he could not personally see them all, so he sent Snow to treat the many coal miners who had fallen sick at the Killingworth Colliery. There was little that Snow could do to help the stricken miners, because the usual treatments for disease-bleeding, laxatives, opium, peppermint, and brandy -- were ineffective against cholera.

Snow continued to treat cholera patients until February of 1832, when the epidemic ended as suddenly and mysteriously as it had begun. By that time, it had left fifty thousand people dead in Great Britain.

During the next sixteen years, Snow earned an M.D. degree, moved to London, became a practicing physician, and distinguished himself by making the first scientific studies of the effects of anesthetics.  By testing the effects of precisely controlled doses of ether and chloroform on many species of animals, as well as on human surgery patients, Snow made the use of those drugs safer and more effective. Surgeons who wished to anesthetize their patients no longer risked killing them by the unscientific application of chloroform-soaked handkerchiefs to their faces.px

Snow remained a bachelor, with extremely regular habits; his social life consisted mainly of discussing ideas at the regular meetings of the Royal Medical and Chirurgical Society.

He did a lot of thinking about the possible causes of contagious diseases, and he came to the unconventional conclusion that they might be caused by invisibly tiny parasites. This was not an original idea, but it was an unpopular one during the first half of the nineteenth century. The "germ theory" of disease had first been proposed in ancient times, and the discovery of microscopic organisms in the late 1600s had made the theory seem plausible, but no one had ever proved that miniature organisms could make people sick.

In Snow's day most physicians believed that cholera was caused by "miasmas" -- poisonous gases that were thought to arise from sewers, swamps, garbage pits, open graves, and other foul-smelling sites of organic decay.

Snow felt that the miasma theory could not explain the spread of certain diseases, including cholera. During the outbreak of 1831, he had noticed that many miners were struck with the disease while working deep underground, where there were no sewers or swamps. It seemed most likely to Snow that the cholera had been spread by invisible germs on the hands of the miners, who had no water for hand-washing when they were underground.

In September of 1848, when Snow was thirty-five, a new outbreak of cholera struck London. He decided to track the progress of the disease. to see if he could determine exactly how it was spread. He learned that the first victim, John Harnold, a merchant seaman, had arrived from Hamburg by ship on September 22. Harnold had gone ashore and rented a room in the London community of Horsleydown where he had quickly developed cholera symptoms and died.

Snow spoke with the attending physician who, just a few days after Harnold's death, had been called back to the same room to treat another man, named Blenkinsopp, who had rented the room after Harnold Blenkinsopp had contracted cholera shortly after renting the room and had died eight days later.  Snow viewed the second death as strong evidence of contagion. He suspected that the room had not been cleaned after Harnold's occupancy and that perhaps some cholera germs had remained in the bed linen.

As more cases appeared, Snow began examining sick patients. All of them reported that their first symptoms had been digestive problems. Snow reasoned that this proved that the disease must be ingested with polluted food or water. If the victims had absorbed cholera poison from polluted air, as the "miasma" theorists believed, then their first symptoms should have appeared in their noses or lungs -- not in their digestive tracts.

Snow theorized that the extreme diarrhea that characterized the disease might be the mechanism that spread the germs from one victim to another. Perhaps the fatal germs were lurking in the great volumes of colorless fluid that patients expelled. If just a few drops of that fluid contaminated a public water supply, the disease germs could be spread to countless new victims.

Snow discussed his theory with colleagues. He searched through medical journals and government reports about cholera looking for references to water conditions and sewer facilities, and he sent written queries about water conditions and sewer facilities to authorities in areas with high mortality from the disease.

In August of 1849, during the second year of the epidemic, Snow felt obliged to share what he considered convincing evidence that cholera was being spread through contaminated water. At his own expense he published a pamphlet entitled On the Mode of Communication of Cholera. Thirty-nine pages in length, the essay contained both a reasoned argument and documentary evidence to support his theory. As one example he cited the case of two rows of houses in a London neighborhood that faced each other. In one row many residents became cholera victims, while in the other row only one person was afflicted. It was discovered, Snow wrote, that "in the former bowl the slops of dirty water, poured down by the inhabitants into a channel in front of the houses, got into the well from which they obtained their water." Snow realized that such conditions existed in many neighborhoods and that if cholera epidemics were ever going to be eliminated, wells and water pipes would have to be kept isolated from drains, cesspools, and sewers.

To avoid antagonizing the majority of physicians who rejected the theory that germs can cause disease, Snow did not directly state his view that a living organism caused cholera. Instead, he wrote of a "poison" that had the ability to "multiply itself by a kind of growth" within the membranes lining the digestive tracts of cholera victims, before being spread to new victims via polluted food or water.

Snow's pamphlet had little effect on the thinking of his colleagues. It was just one of many tracts being published either as pamphlets or as articles in medical journals. A review in the London Medical Journal in September of 1849 complimented Snow for "endeavoring to solve the mystery of the communication of cholera," but the reviewer added that "other causes, irrespective of the water, may have been in operation" and that Dr. Snow could "furnish no proof whatever of the correctness of [his l views."

Snow decided to publicize his views by giving lectures. At a talk to the Western Literary Institution on October 4 and in another talk to the Westminster Medical Society on October 13, he gave more examples with detailed descriptions of cases in several locations; but his views were met with skepticism. Each of Snow's colleagues had his own set of experiences to draw on. Dr. James Bird, for example, agreed that cholera might be communicated from person to person "under favorable conditions," but he disagreed that drinking water had "more than partial effect on spreading cholera." Dr. Lancaster pointed out that Snow's theory required the existence of "some sort of poison," whereas "no such poison has yet been demonstrated to exist."

From the last month of 1849 until late in 1853, Britain experienced few cases of cholera. Snow continued to work on his theory that drinking water was the primary means of contagion. He accumulated data that had been collected in the epidemic of 1848-49 and that showed that patterns of the disease could be linked with specific water supplies. He also continued his pioneering studies of the effects of precisely measured doses of anesthetics.

Other physicians remained highly skeptical of Snow's germ theory of cholera, but everyone praised his work on anesthetics that won him a reputation as the world's leading expert on their use. On April 7, 1853, he administered chloroform to Queen Victoria at the birth of her eighth child, Prince Leopold.

End of Part One

Part Two of Father of Modern Epidemiology

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