“Under the Spell of a Theory”


Johnson’s wonderful book is part mystery, part history, part philosophy of science, and part musing on political philosophy.  The passage below warms the heart (and stimulates the brain) of the libertarian.  Against great odds, Dr. Snow persisted in presenting ever-more convincing evidence for his correct water-borne theory of cholera.  Meanwhile Chadwick, the main advocate of government public health activities, continued to direct policy on the basis of the mistaken theory that cholera was spread by foul vapors in the air. 


(p. 120) Herein lies the dominant irony of the state of British public health in the late 1840s.  Just as Snow was concocting his theory of cholera as a waterborne agent that had to be ingested to do harm, Chadwick was building an elaborate scheme that would deliver the cholera bacteria directly to the mouths of Londoners.  (A modern bioterrorist couldn’t have come up with a more ingenious and far-reaching scheme.)  Sure enough, the cholera returned with a vengeance in 1848-1849, the rising death toll neatly following the Sewer Commission’s cheerful data on the growing supply of waste deposited in the river.  By the end of the outbreak, nearly 15,000 Londoners would be dead.  The first defining act of a modern, centralized public-health authority was to poison an entire urban population.  (There is some precedent to Chadwick’s folly, however.  During the plague years of 1665-1666, popular lore had it that the disease was being spread by dogs and cats.  The Lord Mayor promptly called for a mass extermination of the city’s entire population of pets and strays, which was dutifully carried out by his minions.  Of course, the plague turned out to be (p. 121) transmitted via the rats, whose numbers grew exponentially after the sudden, state-sponsored demise of their only predators.)

Why would the authorities go to such lengths to destroy the Thames?  All the members of these various commissions were fully aware that the waste being flushed into the river was having disastrous effects on the quality of the water.  And they were equally aware that a significant percentage of the population was drinking the water.  Even without a waterborne theory of cholera’s origin, it seems like madness to celebrate the ever-increasing tonnage of human excrement being flushed into the water supply.  And, indeed, it was a kind of madness, the madness that comes from being under the spell of a Theory.  If all smell was disease, if London’s health crisis was entirely attributable to contaminated air, then any effort to rid the houses and streets of miasmatic vapors was worth the cost, even if it meant turning the Thames into a river of sewage.



Johnson, Steven. The Ghost Map: The Story of London’s Most Terrifying Epidemic – and How It Changed Science, Cities, and the Modern World. New York: Riverhead Books, 2006.


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