In elaborating somewhat briefly the conception of the various psychoses generally accepted by American psychiatrists, and for that reason included in the classification adopted by the Association, every effort has been made, as far as possible, to show the steps which have led up to present developments. The author has endeavored to confine himself to reflecting the views of others throughout and has used actual quotations from recognized authorities as far as was deemed advisable. In the discussion of the various psychoses frequent references will be noted to the description of the various clinical groups contained in the manual prepared by the Committee on Statistics for the American Psychiatric Association. As is shown in the manual, these definitions and explanatory notes were formulated by Dr. George H. Kirby. Special reference should be made to the important contributions to the literature of psychiatry of such well-known American writers as Meyer, Hoch, Kirby, White, Barrett, Campbell, Southard, Peterson, Diefendorf, Jelliffe, Paton, Salmon, Russell, Buckley, Rosanoff, Orton, Singer and many others. The work of Kraepelin, Bleuler, Nissl, Alzheimer, Freud, Jung, Stekel, Janet and others abroad has exercised an influence on the psychiatry of the day which must be recognized. We are very largely indebted to Pollock and to Furbush for the available information relating to the incidence of the various psychoses in this country. To the American Psychiatric, for many years the American Medico-Psychological, Association we owe an exhaustive historical review of the institutional care and treatment of mental diseases in the United States and Canada. Obviously this work was not intended as a textbook, nor was it designed to serve the purpose of one. It is an appeal to those who are already familiar with the fundamental principles of psychiatry. For that reason the interpretation of mental mechanisms given so much space in textbooks has been entirely omitted and no reference is made to the treatment of the individual psychoses. Such reliable statistical data as could be gathered from recent hospital reports and publications have been utilized in full. The following institutions were represented in this study: 1. MASSACHUSETTS—fourteen hospitals (1919-1920): Boston State Hospital, Boston; Bridgewater State Hospital, State Farm; Danvers State Hospital, Hathorne; Foxborough State Hospital, Foxborough; Gardner State Colony, Gardner; Grafton State Hospital, North Grafton; McLean Hospital, Waverley; Medfield State Hospital, Harding; Monson State Hospital, Palmer; Northampton State Hospital, Northampton; State Infirmary, Tewksbury (Mental Wards); Taunton State Hospital, Taunton; Westborough State Hospital, Westborough; Worcester State Hospital, Worcester.