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respond in usefulness with the notification and early discovery of plague cases among human beings. It would then be possible to concentrate, with precision, attention on the infected localities and bring special measures to bear on them, with the view of destroying the rats and their infection before these localities became dangerous in any high degree to man. In connection with the habits of rats it may be mentioned here that whenever rats begin to die in numbers, whether from disease or poison, there is a disposition for the others to emigrate from that locality in a more or less distinctly defined direction. This phenomenon of migration should be borne in mind and watched so that on its first appearance the rats coming into a healthy locality may be destroyed.

5. These measures would not interfere with, but should go on side by side with the more general destruction of rats throughout the town and district carried out by the public, the object of which is to destroy the underground agents which are susceptible to the disease and thus prevent the infection from being disseminated further than the already infected areas. If the rats and mice are destroyed in a locality before plague is imported, plague becomes comparatively a manageable disease.

6. The methods of destruction at the disposal of the public are of a limited nature, consisting mainly of the laying down of poison such as arsenic and phosphor- ous, the employment of rat traps, the pouring of crude carbolic acid down the runs of rats and the killing of them when they endeavour to escape, and, in the case of large firms with godowns and warehouses, the employment of rat-catchers. The methods at the disposal of the sanitary authority are also somewhat limited but can be carried out in a more systematic manner. They consist in the pumping of car- bonic acid gas or sulphureous acid gas into small sections of drains and sewers previously blocked up for that purpose, and into the holds of ships and boats infested with rats, the employment of rat-catchers on special areas, the taking up ground floors in infected houses, demolition of the rat runs and the setting up of another slightly infectious disease among rats which is not communicable, like plague, to other animals or to human beings. This disease can be produced by feeding rats with cultures of a coccobacillus discovered by DAnysz.

7. No single method is altogether satisfactory in getting rid of all the rats, healthy and unhealthy, but each method when employed systematically materially assists in obtaining that object, and the continuous regular and systematic em- ployment of all these methods in a district ultimately produces excellent results.

8. For the preparation of DANYSZ virus to be employed to set up disease among rats and mice, I would advise that the services of Dr. HUNTER, the newly appointed bacteriologist to the Colony, be made use of and be placed at the disposal of the Sanitary Board for the time being. I would further advise that thousands of doses of this virus be systematically distributed in different parts of the town not only during every day of the plague season but throughout the whole year in order that an impression may be made on the enormous number of rats which exist in Hong- kong.

9. This desirable result will not be effected in Hongkong unless special mea- sures are at the same time taken at the wharves and landing stages to prevent healthy or sick rats from being imported. Every newly arrived ship moored at the landing stages, without being subjected to precautionary measures, adds its quota of fresh rats to the warehouses and godowns. This is a matter for careful considera- tion, and precautions similar to those taken in other ports should be introduced at the landing stages and wharves of Hongkong and Kowloon.

10. Once the requisite measures are taken against rat plague, which, some times, in addition to the foregoing, necessitate the evacuation of a badly infected area in order to save the inhabitants from being extensively attacked with plague,