The following list of the more common mental diseases is based upon the classification offered by the National Committee for Mental Hygiene. _Psychoses_ General Paresis Alcoholic Hardening of the Brain Arteries Senility Involutional Melancholia Manic-Depressive Schizophrenia _Psychoneuroses_ Hysteria--anxiety, conversion Hypochondriasis _Mental Deficiency_ _Behavior Disorders_ Maladjustment Habit or conduct disturbance _Psychopathic Personality_ Amoral, immoral, emotional Detailed descriptions are confusing to the layman because within one disease subclass, the variations possible as a result of duration, time of onset, mental background, etc. are very great. Only generalizations will be mentioned. The two major divisions of mental disease--psychosis and psychoneurosis--are not always readily differentiated. In the psychotic, the personality is usually distorted, whereas in the psychoneurotic the personality remains normal in relation to the realities of the world and social life. The psychotic is the more obviously deranged, the psychoneurotic usually passes for almost normal. _General Paresis_ is a late result of syphilis. The patient becomes increasingly forgetful and disinterested in his surroundings and social relations. There is a gradual loss of judgment and other mental faculties. The facial expression becomes empty and the speech slurred. This is the disease in which the knee reflex disappears, an indication popularly associated with “crazy people”. It is a progressive disease which becomes more difficult to treat as it progresses. The treatment at this writing consists of the use of drugs containing arsenic and the production of fever in the patient. The results are not remarkable, ordinarily. Return to normal is unusual. Music for such patients could in no manner be conceived as curative or even helpful.