John Snow Investigates a Cholera Outbreak

On the final day of August 1854, a severe cholera outbreak emerged in the Soho district of London, near Broad Street and Golden Square. Snow's own tally recorded 127 deaths on 2 September alone, and within six days more than three quarters of the inhabitants of the worst-affected streets had fled. Snow counted upwards of 500 fatal attacks within ten days, and his table of the outbreak eventually listed 616 deaths before the localized epidemic subsided. The crisis struck an overcrowded urban quarter where cowsheds, slaughterhouses, and overflowing cesspools beneath cellar floors drained directly into an inadequate drainage system, while city authorities disposed of waste into the River Thames.

At that time, prevailing medical orthodoxy attributed epidemic diseases to miasma, an atmospheric contamination of noxious particles emitted by decomposing organic substances. Prominent figures such as Dr William Farr initially maintained that soils around the Thames released these airborne poisons, advocating for sanitation through general cleansing rather than biological inquiry. In opposition to this consensus, the physician John Snow argued that cholera stemmed not from bad air, but from an unisolated morbid matter ingested through contaminated food or water. Snow had articulated this hypothesis in an 1849 publication, though, as the London Museum notes, he was mostly ignored by the medical profession.