Students of the history of American legal problems realize that, in harmony with the economic changes that have taken place during the past century, the interpretation of the constitutional limitations of the federal government is becoming correspondingly and progressively more liberal. Few persons interested in national welfare from the standpoint of public health are accustomed to ask themselves whence the necessary legal authority for the enforcement of hygienic measures is derived. Yet, as we are living under a constitution that permits the federal government to exercise only those powers clearly granted to it by that instrument, it is important to know the legal basis for permissible sanitary measures.