No study presents more important and difficult sanitary problems than the lines of march taken by bubonic plague during the past fourteen years in its advance from the remote endemic focus of the disease in the province of Yunnan, China, to the numerous countries in all quarters of the globe, where by epidemic expansion plague has appeared and in many instances established itself in defiance of the most carefully planned preventive measures. 1894. The revival of plague dates from the year 1894, when, escaping from the western Chinese province of Yunnan, it reached Canton, an important city and seaport of southern China. The first public knowledge of plague in Canton was in January, 1894, when Dr. Mary Niles was called to see General Wong's daughter-in-law, who was suffering from an inguinal bubo and grave constitutional symptoms. The escape of plague from its endemic foci is not in itself an unusual event. It appears to be established that there are two distinct" strains" of plague, differing in the location of their permanent homes and in the facility for spreading outside the endemic foci. One of the endemic homes of plague is in western Asia. The" strain" lodged there does not possess the same power of diffusion as the Indo-Chinese" strain." It was the Indo-Chinese variety which, escaping from its endemic center in Yunnan, gave rise to the present pandemic. From 1879 to 1894 not a single year passed without the appearance of plague in some locality distant from endemic plague centers. India, Japan, Arabia, Persia, and Russia were thus invaded, but the disease did not develop pandemic proportions. The startling fact about the excursion of plague in 1894 is that it did not limit itself to the locality primarily visited, but began a series of ramifications that have since become world-wide. In 1894 plague was introduced from Canton into the neighboring island of Hongkong, a journey by water of about eight hours. During the height of the epidemic it was almost a daily event for deaths to occur en route from Canton to Hongkong. A rough estimate gives the number of deaths in Canton as 120,000 between March and August. All classes among the native population suffered, and rats were observed to be affected; but in the foreign quarter of Canton, with a population of about 300, not a single case occurred.