I took great care to ascertain the nature of the water supply correctly in every instance. I did not rest content with the mere reply of the resident, or the appearance of the water, without other evidence, such as the production of the receipt for the water rate. I was also assisted very much by the application of a chemical test to the water, for throughout all the dry weather, which lasted whilst my inquiries were being made, a mixture of sea water extended further up the Thames than usual, and the water of the Southwark and Vauxhall Company contained nearly forty grains of common salt per gallon, whilst that of the Lambeth Company contained only ·95 of a grain. These analyses were verified in numerous cases where the source of the water could be proved clearly by other evidence. For the first four weeks of the epidemic I employed the list of deaths from cholera published in the Weekly Returns of the Registrar-General, and for the next three weeks, during which my inquiry extended, I was kindly permitted to copy the addresses of persons dying of cholera at the General Register Office. My personal inquiry extended over every subdistrict to which the supply of the Lambeth Water Company extended, and it, therefore, included all the area in which the supply of the two companies was intermixed in the manner explained above. At the time I was making my inquiry, the entire number of houses supplied by each water company was known, from a return made to Parliament, but the number of houses supplied in each district and subdistrict by each company respectively was not known. In order, therefore, to see the exact bearing of my results, I found it desirable to extend the inquiry over the districts supplied exclusively by the Southwark and Vauxhall Company; for this purpose I obtained the assistance of Mr. Whiting, a medical man, who took great pains with his part of the inquiry, which was merely to ascertain whether the houses in which fatal attacks had taken place were supplied by the Southwark Company, or from some other source, as a pump well or tidal ditch. His inquiry extended over the first four weeks of the epidemic.