On the Mode of Communication of Cholera

Snow expanded his reports on his cholera research in a book entitled On the Mode of Communication of Cholera published in London the same year. That book contained more statistical data confirming his theories. Over the next five years Snow continued his research, publishing a second edition of the book in 1855. This was so greatly revised and expanded that it was essentially a new work. In it Snow set forth his views of the etiology and spread of cholera, which he believed to be caused by a living organism (a belief confirmed by Koch's discovery of the cholera vibrio in 1883), and included statistical surveys made during the great cholera epidemic of 1854, demonstrating that the number of cholera deaths in each area of southern London corresponded to the degree of contamination of the local drinking water. This 1855 edition was the first to tell the dramatic story of the Broad Street pump, which, after contamination with sewage from a nearby pipe, caused 500 cholera deaths within the space of ten days. Once the epidemic had peaked, Snow persuaded the parish councilors to remove the pump handle, and the number of cholera attacks decreased rapidly. Snow's report of the Broad Street epidemic included a spot-map of the district showing the location of each pump and fatal cholera cases-- the first use of a spot-map in epidemiology.--J. Norman, 2006.