John Snow, born in 1813, was the son of a coal-yard laborer in York, England. Snow planned to become a physician, and at fourteen, he was apprenticed to Dr. William Hardcastle. During his early years as an apprentice, he filled notebooks with his thoughts and observations on scientific subjects. 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.
Snow began to do 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 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.
Snow's research remains extremely relevant today, necessitating sanitary septic infrastructure in any populated area. The pathogen Vibrio cholerae is not contagious from body to body but is easily spread through food and water sources that become contaminated with sewage. The conditions necessary to induce a cholera outbreak still exist in many countries where hygienic water sources are not readily available. The largest outbreak in modern history occurred months after the 2010 Haitian earthquake. 6,631 deaths were recorded among the 470,000+ reported cases. The Centers for Disease Control and Prevention (CDC) soon went to work, establishing guidelines for cholera treatment and avoidance as well as setting up sanitation facilities. $75 million has been spent by the US government in attempts to control the disease but Haiti will likely continue to have increased cholera transmissions far into the future. Educating people in hygienic practices can only go so far. Efficient water and sewage infrastructure is vital to reducing the impact of the disease. John Snow was the first to recognize the importance of a clean water supply after investigating the cholera outbreaks of 1800s London. His work was the first step into requiring strict government and city maintenance of water resource structures.