There are many reasons why every hospital of any consequence that is engaged in the care of mental diseases should be provided with a well trained and experienced pathologist. Examinations of urine and sputum must be made daily. Widal tests are sometimes necessary for the diagnosis of typhoid fever. Analyses of water and milk should be made at frequent intervals. Bacteriological vaccines should be available at any time. Only laboratory investigations can throw any light on the source of the frequent infections which are found in large institutions. Diphtheria is a disease which must be guarded against constantly. Lumbar punctures, Wassermann tests, the colloidal gold reaction, cell counts, etc., are daily necessities in a large hospital. We lose much information of value to us if autopsies are neglected. A definite program of pathological research work should be carried on in every hospital for mental diseases. It has been suggested frequently that the microscope has no part to play in studying the etiology of the psychoses and that they are purely functional in origin. Many of them are functional. It is nevertheless equally true that we have a definite pathological basis for the traumatic psychoses, the senile conditions, cerebral arteriosclerosis, general paresis, brain syphilis, cerebral growths, mental deficiency and many other brain and nervous diseases. The psychosis most clearly understood from the standpoint of etiology, pathology, symptomatology and diagnosis is general paresis. Our definite knowledge of that condition was obtained entirely from the laboratory. Further information may be secured in the same way. While it is true that we have not had any great amount of success as yet with the treatment of general paresis with salvarsan, the positive knowledge that the disease is of syphilitic origin should encourage us in our efforts to solve the problem of curing it. Histological, pathological, bacteriological, chemical, clinical and psychological researches must be pushed vigorously if psychiatry is to keep pace with the general progress shown by modern medicine in other fields.