In our hospitals for some years past, we have studied both the intellectual and temperamental make-up of the first admissions and have tried to apply uniform standards throughout the service. In 1920 it was found that of the ascertained cases 61 per cent were temperamentally normal and 88 per cent were rated as intellectually normal. Only about 7 per cent of the patients were both temperamentally and intellectually abnormal. The proportion of patients with abnormal make-up varied considerably in the different groups of psychoses. For example, in the dementia-praecox group in 1920, 61 per cent were rated as temperamentally abnormal while in the manic-depressive group only 33 per cent were so rated. The absence of marked abnormalities in individuals prior to the onset of the psychosis cannot be construed as conclusive evidence that there are no hereditary defects in the make-up, neither can the development of the psychosis be taken as proof of a defective constitution. All the facts in connection with the onset of the mental disorder and previous reactions must be brought together before the constitutional make-up of the patient can be positively determined. Psychiatrists have recently emphasized the connection between bodily states and behavior and the importance of the sexual and endocrine organs in relation to the psychoses. What part of the disorders related to these organs is due to hereditary and what part to environmental factors have yet to be determined. Notwithstanding these and many other complications, there is abundant evidence that mental disorders occur much more frequently in some family stocks than in others, and that prolonged inbreeding of degenerate stocks is productive of most disastrous results. With the limited knowledge at hand, what is to be done to lessen the burdens imposed on society by the prevalence of mental disease? Three lines of action are suggested: 1. Environmental stresses may be lessened and natural resistance strengthened. 2. Procreation of defective stock may be checked. 3. Procreation of normal stock may be increased. The methods now in use to prevent physical disease may be applied to a considerable extent in preventing mental disease. They include the dissemination of knowledge of hygiene and sanitation, prompt treatment of incipient diseases, segregation of those suffering from contagious diseases, and immunization of those liable to exposure to pathogenic germs. Another line of attack consists in safeguarding the public from injurious food and artificial beverages and from polluted air and water. The abolition of the liquor traffic and the movement to check the spread of syphilis are examples of effective work along these lines.