F ive years have passed since the publication of the first edition of Mouth Hygiene, and during that period a number of schools have been organized for the education and training of the dental hygienist. The experience of these schools has shown that several of the funda mental subjects, such as anatomy, physiology, bacteriology, hygiene etc., require more extensive text than could be adequately covered in any one book. It is, therefore, recommended that standard text-books be utilized for such subjects. The second edition of Mouth Hygiene endeavors to meet the need of the dental hygienist for those subjects which pertain directly to dentistry and which are essential to her education.