Britain was struck by four cholera epidemics between 1831 and 1867. Although it was an age of fatal infectious diseases, none was as gruesome as this exotic import from darkest Asia. It began with violent stomach cramps and diarrhoea, and the patient died swiftly (though far from painlessly) from acute dehydration. The disease spread like wildfire through communities, and entire neighbourhoods were wiped out in a matter of days. There was no cure and no consensus on how to prevent it. The majority of Victorian doctors thought that the disease was spread by a miasmic influence carried by foul air. The idea was far from implausible, especially since the filthiest parts of towns seemed to be most vulnerable to the disease. 

This book is about the nineteenth-century doctor who did more than anybody else to undermine that theory. John Snow (1813–58) was a general practitioner of humble origins, and his early career was entirely ordinary. The only remarkable things about the young medical apprentice were his vegetarianism and teetotalism. When chemical