There is no such thing in medical literature as an insistent demand from the profession for new volumes upon old topics. Authors need not hope, therefore, to create the impression that they are meeting long-felt though unexpressed wants of medical readers in launching new books. On the other hand, the creator of a new volume upon an old subject should seek justification for literary paternity in the progressive changes in the status of our knowledge of disease, its causes, prevention, and cure. Such changes are admittedly going on with a certain degree of constancy and at such a rate of frequency that new presentations of old themes, are both justified and desirable from time to time. With this idea in mind and with the desire to present, in useful and practical form, a work which shall contain at least some unhackneyed material and which shall represent modern studies and a record of actual control work done in this justly-dreaded disease, the following pages are submitted to the medical profession and to sanitarians generally. With a profound respect for the laboratory worker and his work and with a profound conviction that to him belongs the greater measure of credit for real accomplishment in connection with plague up to the present time, I desire to insist that the true utility of knowledge gained within laboratory walls lies in its intelligent application in the outer world and that ofttimes this application must be made by men who are themselves without extended laboratory training. An appreciation of principles--with an intelligent ability to accept, to appropriate, to apply and, most of all, to refrain from entering without due preparation the domain of the laboratory worker--is an indispensable requisite in the equipment of the practical sanitarian, upon whom must fall the responsibilities of success or failure in combating the disease we are now to consider. During the past fourteen years it has been my privilege to observe two epidemics of plague in the Philippine Islands. Some of these observations were made in the capacity of a military medical officer, but my later observations, upon which this report and study are chiefly based, were made from the view-point of a civil health officer. At different times I have been called upon to deal with the disease both as sanitary officer and clinician, and from October, 1912, to July, 1914, I had charge of all plague suppressive measures in Manila. In 1914 I was also in charge, as acting chief, of the San Lazaro Hospitals Division of the Bureau of Health, Manila, where all cases of plague are brought, either for treatment or autopsy.