HYGIENE HAS BEEN DEFINED as "the branch of medical science pertaining to the preservation of health." Some of the factors and practices that influence the development and maintenance of physical health are nutrition, sleep and rest, exercise, fatigue, disease and infection, accidents, drugs and narcotics. Abundant research into each of these factors has been made and continues to be made. Because of the highly technical nature of many of these studies, it is deemed inappropriate to include them in this chapter. Readers interested in research in the physiology of the human organism are therefore referred to basic references in the fields of physiology, nutrition, and bio-chemistry, and to the medical science periodicals. Health education has been defined as the sum total of all experiences that contribute toward the development of individual and group practices, attitudes, and knowledge that make for better personal, community, and racial health (812). It is conceived more and more as the creation of conditions and experience that will foster good physical and mental health. The preceding summary of studies in the area of health and physical education appeared as Chapter V by Strang and Lane in the REVIEW OF EDUCATIONAL RESEARCH for December 1937, and reviewed the literature up to July 1937. Since that time more than two hundred and fifty articles have appeared under the titles of physical hygiene and health education (785). While the mass of this material does not deal with research as such, it does indicate the scope of interest in this area. The bulk of the references cited in this chapter pertain to health education, rather than to physical hygiene, for the reason given above.