||32 TWENTIETH ANNUAL REYNOLDS LECTURE a gene does or does not do leads to a treatment which could prevent otherwise normal children from suffering varying stages of mental impairment. The genetics of the two most common types of insanity, schizophrenia and manic depressive insanity, have been studied by different investigators. It is agreed by many geneticists that they both have an hereditary basis, but that environment also plays an important role. The investigators do not agree, however, on any one pattern of inheritance. Huntington's Chorea, which is responsible for another type of insanity, is inherited as a Mendelian dominant. The whole subject of the genetics of mental health is a fertile field for further study. Most of the traits so far discussed deal with abnormal or objectionable characteristics. Gene action, however, is not restricted to these. Geneticists generally believe that special talents such as exceptional artistic and musical abilities are in part, at least, gene-determined. Just how much heredity is responsible for intelligence or native ability no one as yet seems to have been able to demonstrate. That it plays an important role few will deny. Probably it sets limits between which environmental factors may determine the intelligence level of an individual. Not until psychologists are able to analyze intelligence and break it down into its component parts will we be able to determine the part heredity plays in its determination. In most instances it is impossible to unravel complicated cases involving genetics in man. They undoubtedly occur, however, the same as they do in plants and other animals where test crosses and large numbers can be obtained. Multiple factors are undoubtedly involved in such traits as skin color and bodily conformation, and complicated genetic patterns are undoubtedly involved in other hereditary traits. Studies in plant and animal genetics help us by comparison to realize the many complexities which must also be occurring in man. We have attempted, largely by citing examples, to show the importance of heredity in the life of man. To a large extent it is responsible for not only his physical characteristics, but for his physiological characteristics as well. Either directly or indirectly it is a definite factor in determining man's intellectual level and his possession of special talents.