"The different behavior of Hamburg and Altona as regards cholera is extremely interesting. The two towns adjoin; they are practically one city. The division between the two is no more obvious than that between two densely peopled London parishes, and yet a spot map indicating the houses which were attacked with cholera, which was shown to me by Professor Koch, points out clearly that whereas the disease prevailed in epidemic form on the Hamburg side of the boundary line, that line running in and out among the streets and houses and at times passing diagonally through the houses themselves, formed the limit beyond which the epidemic, as such, did not extend. The dots on one side of the dividing line were proof of the epidemicity of cholera in Hamburg, their comparative absence on the Altona side of it was proof of the absence of the epidemic in Altona. To use Professor Koch's own words: 'Cholera in Hamburg went right up to the boundary of Altona and then stopped. In one street, which for a long way forms the boundary, there was cholera on the Hamburg side, whereas on the Altona side was free from it, and yet there was one detectable difference, and one only, between the two adjacent areas—they had different water services.' Professor Koch has collected certain proofs which he regards as crucial on this point, and Dr. Reincke has supplied me with a small plan in support of the contention. At one point close to and on the Hamburg side of the boundary line between Hamburg and Altona, is a large yard, known as the Hamburger-Platz. It contains two rows of large and lofty dwellings, containing 72 separate tenements and some 400 people, belonging almost wholly to those classes who suffered most from cholera elsewhere in Hamburg. But while cholera is shown by the spot map to have prevailed all around, not a single case occurred among the many residents of this court during the whole epidemic. And why? Professor Koch explains that owing to local difficulties, water from the Hamburg mains could not easily be obtained for the dwellings in question, and hence a supply had been laid in from one of the Altona mains in an adjacent street. This was the only part of Hamburg which received Altona water, and I am informed that it was the only spot in Hamburg in which was aggregated a population of the class in question, which escaped the cholera. At the date of my visit to Hamburg, a notice board was affixed at the entrance to this court. It stated that certain tenements were to let; but, above all, in large type, and as an inducement to intending tenants, was the announcement that the court was not only within the jurisdiction of Hamburg, with the privileges still attaching to the old Hanseatic cities, but that it had a supply of Altona water. During the epidemic the deaths in the several cities were: