Toward the end of August, 1909, a sudden increase in the number of cases of typhoid fever reported from the boroughs of Manhattan and the Bronx attracted attention, and led to an investigation to ascertain the cause of the infections. A rapid survey of the cases showed that a certain milk-supply was common to almost all, and accordingly, September 1, the suspected supply was shut off. From the infections which had already occurred, however, additional cases came to be reported all through September, the total number belonging to this outbreak finally numbering several hundred. Some idea of the havoc wrought by this infection can be obtained by a glance at Table 1, in which are shown the cases of typhoid fever reported, week by week, in each ward, commencing August I, and (in parenthesis) the average normal incidence of typhoid fever for the ward, based on the experience of the