312 PATHOGENIC BACTERIA. year when there are not at least some cases of cholera in the city. The frequent pilgrimages and great festivals of the Hindoos and Moslems, by bringing together an enormous number of people who crowd in close quarters where filth and bad diet are common, cause a rapid increase in the number of cases during these periods and the dispersion of the disease when the festivals break up. The disease extends readily along the regular lines of travel, visiting town after town, until from Asia it has frequently ex- tended into Europe, and by the steamships plying on foreign waters has been several times carried to our own continent and to the islands of the seas. Many cases are on record which show conclusively how a single ship, having a few cholera cases on board, may be the cause of an outbreak of the disease in the port at which it arrives. It seems strange to us now, with the light of present information illuminating the pages of the past, to observe how the distinctly infectious nature of such a disease could be overlooked in the search for some atmospheric or climatic cause, some miasm, which was to account for it. The discovery of the organism which seems to be the specific cause of cholera was made by Koch, who was appointed one of a German cholera-commission to study the disease in Egypt and India in 1883-84. Since his discovery, but a decade ago, the works upon cholera and the published investigations to which the spirillum has been subjected have produced an immense literature, a large part of which was stimulated by the Hamburg epidemic of a few years ago. The micro-organism described by Koch, and now gen- erally accepted to be the cause of cholera, is a short individual about half the length of a tubercle bacillus, considerably stouter, and distinctly curved, so that the original name by which it was known was the " comma bacillus" (Figs. 80, 81).