her daughter Beatrice in 1857. This led to wider acceptance of obstetrical anaesthesia. Cholera Snow was a skeptic of the then-dominant miasma theory that stated that diseases such as cholera and bubonic plague were caused by pollution or a noxious form of "bad air". The germ theory of disease had not yet been developed, so Snow did not understand the mechanism by which the disease was transmitted. His observation of the evidence led him to discount the theory of foul air. He first published his theory in an 1849 essay, On the Mode of Communication of Cholera, followed by a more detailed treatise in 1855 incorporating the results of his investigation of the role of the water supply in the Soho epidemic of 1854. By talking to local residents (with the help of Henry Whitehead), he identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street). Although Snow's chemical and microscope examination of a water sample from the Broad Street pump did not conclusively prove its danger, his studies of the pattern of the disease were convincing enough to persuade the local council to disable the well pump by removing its handle (force rod). This action has been commonly credited as ending the outbreak, but Snow observed that the epidemic may have already been in rapid decline: Snow later used a dot map to illustrate the cluster of cholera cases around the pump. He also used statistics to illustrate the connection between the quality of the water source and cholera cases. He showed that homes supplied by the Southwark and Vauxhall Waterworks Company, which was taking water from sewage-polluted sections of the Thames, had a cholera rate fourteen times that of those supplied by Lambeth Waterworks Company, which obtained water from the upriver, cleaner Seething Wells. Snow's study was a major event in the history of public health and geography. It is regarded as the founding event of the science of epidemiology. Snow wrote: Researchers later discovered that this public well had been dug only from an old cesspit, which had begun to leak faecal bacteria. The cloth nappy of a baby, who had contracted cholera from another source, had been washed into this cesspit. Its opening was originally under a nearby house, which had been rebuilt farther away after a fire. The city had widened the street and the cesspit was lost.