This furnishes teachers of physical education with a codification of the principles and practices, including history, scientific basis, aims, content and methods in the field of physical education, and a text and guide in the natural program, which "has now had fifteen years of earnest, devoted, scientific research in the formulation, application and testing of theory and practice." The authors make a distinction between the natural program, which has its origin in the natural impulses and instincts of the human being, and the naturalized program of physical education, which gives recognition to and makes provision for modifications, adoptions and additions arising from racial, national, community, vocational, avocational and individual needs in our present civilization. The apparent interchangeability of the terms "natural" and "naturalized" is not a little confusing, although careful study seems to indicate that "naturalized" is the more comprehensive term. As a fundamental objective, the demand is made for