In my opinion, the day has arrived when we may properly exclude from such handbooks as this one (intended for practical guidance), all such methods of diagnosis and treatment as have failed to meet the test of actual experience through a reasonable length of time. Twice in recent years,[17] I have described the diagnosis and treatment of plague, attempting in each case to present a reasonably full account of the methods employed and advocated by authorities, for theoretic reasons and from the recorded personal experiences of medical men throughout the world. There comes a time, however, when wheat and chaff must be separated and when methods which have failed, in application, to justify preformed expectations must be relegated to the department of historical medicine. [17] Tropical Medicine (1907) and Hare's Modern Treatment (1911), vol. 1. Judging from recent medical text books it is evident that medical writers are generally accepting this view as the proper one. At any rate, my experiences and those of my medical friends during the Manila epidemic of 1912-1914, have led me to discard as impracticable, unproven, disproven or unpromising, certain plans of treatment formerly deemed worthy of trial. I do not refer to these methods individually but will content myself, instead, with reciting briefly the methods which I believe, from personal experience and the collected experience of others, to be worthy of continuance and of further trial. DIAGNOSIS.--The rapid diagnosis of plague is always of the utmost importance, both from the view-point of prognosis and treatment, in the individual case, and from the community view-point of the recognition of the presence of a dangerous communicable disease, with the resultant obligation falling upon the health authorities. THE BIOLOGIC DIAGNOSIS.--Let us understand, first and finally, that but one diagnosis is absolutely and irrefutably dependable, viz.: the biologic diagnosis. Herein I would include not only the recovery of the pest bacillus from the patient, but the recovery and identification of the organism from inoculated animals, infected from blood, tissues, secretions or cultivated plague bacilli derived from the human patient or cadaver. This entire process involves a lapse of time of several days, and, while it is indispensable in the earliest cases of an epidemic, and highly desirable for the proper study of all cases of plague, it is impracticable and unnecessary, in communities where plague is known to exist, to carry out more than the first steps of the biologic diagnosis, viz.: the recovery of _B. pestis_ (morphologic identification) from the patient.