Dr. Billings was transferred to the Surgeon General's Office in 1864, after his active service as a surgeon in army hospitals and in the field. Under his direction the leading medical library in this country was collected, so complete in fact that the index and catalogue which he compiled from it covered all branches of medical science. During the thirty-one years of his service in the Surgeon General's Office his energy and versatility led him into many fields of study. These included climatology, military hygiene, vital statistics, ventilation and heating, hospital construction, hygiene, vaccination, medical education, the history of medicine, and medical legislation on all of which he contributed essays. As a result he edited a medical dictionary, and compiled bibliographies on alcohol, on care of the insane, feebleminded and other defectives. His broad interests and scholarship were recognized both at home and abroad as indicated by honorary degrees from