What has made plague permanent in Hongkong is the overcrowding of the native districts. Besides there is a floating population entering and leaving the native quarters, numbering about 4000 a day. The native houses have been built with double floors and walls which harbor the rats. Where the construction is of wood it is possible to remove the rat spaces. It has been found since the introduction of plague into Hongkong in 1894, that those districts containing the greatest number of soft brick houses with hollow walls, have shown the greatest incidence of plague. This can not be remedied as it would involve the destruction of buildings on too large a scale. THE WORK OF THE SANITARY BOARD The area under the control of the Board comprises the Island of Hongkong containing 32 square miles, with a sea frontage of 13 miles in length. Included also is the old city of Kowloon which is situated one mile and a third across the harbor and contains two and three-fourths square miles. The city of Victoria on the northern shore of the Island of Hongkong has a sea frontage of 5 miles, contains about ten thousand domestic buildings, of which about one thousand are non-Chinese. The population of Hongkong is difficult to estimate, as the floating population is so great. In the 1912 census there were 446,614 Chinese and 21,163 non-Chinese. The city of Victoria is divided into 10 Urban Health Districts and old Kowloon into 2. There is an inspector in charge of each. These districts are built over an area averaging from 31 to 140 acres. The houses in these districts average one thousand and the population from 8000 to 33,000. There are four inspectors in charge of the scavenging work, one for the disinfection stations in Victoria and old Kowloon, one for the cemeteries and two for general duty. The measures employed by the Sanitary Board are summarized as follows: 1. The exclusion of rats from all dwellings by means of concreted ground surfaces, the protection of all drain openings and ventilating openings by iron gratings, and the prohibition of ceilings and of hollow walls in new buildings and in those existing buildings from which they have been removed by order.