Deaths from Cholera
In Episode II, Snow obtained a list of cholera deaths from the General Register office, the equivalent of a modern vital statistics bureau. The table below presents the General Register office's list of deaths for the four weeks ending August 5, 1854, just before the Broad Street outbreak. Snow supplied this table as an Appendix to his 1855 book, On the Mode of Communication of Cholera, which details all of Snow's studies. This table, then, presents a record quite similar to the record Snow used to investigate the Broad Street eruption.
It is interesting that Snow chose to present in his Appendix a table from the more general epidemic of Summer 1854, which was caused not by a single point source but by the sewage-laden River Thames. Snow must have believed that the scientific methods he used in the more general epidemics would be of more interest than his Broad Street work. Snow has added to the table the name of the company which supplied water to each stricken household, a piece of information that was sometimes quite difficult to obtain. The houses were frequently occupied by renters who did not pay the water bill, and even owners were sometimes unaware of the name of company they paid, unless they could find a receipt. Snow discovered that a chemical test could reliably reveal the water company which supplied a household, and often resorted to that test. Snow used the table below and similar ones to build substantial evidence of an association between water companies drawing sewage-laden water from the Thames, and companies which drew their less contaminated water from above the city. For brevity, our case has not dealt with those investigations, but they were of great significance to Snow, and at least as laudable as his more brief Broad Street work.