INTRODUCTION IT is the aim in The Health Series of Physiology and Hygienen to present in an attractive form for pupils in the elementary school the latest and most accurate knowledge relating to physiology, and especially to the hygiene of daily life. The constant effort of the authors has been to make scientific knowledge so simple, so concrete, and so captivating that pupils can hardly fail to take an interest in the problems of preserving health for the purpose of making the most of life. Throughout the series, the aim has been kept in view of awakening in the young a normal desire to live in such a manner as to develop strength and preserve health, because in this way the individual will have the greatest success in securing the things which he desires, and in avoiding the disabilities and pains which otherwise are likely to occupy a considerable part of his life. Comparatively little attention is given to anatomy, and only suffi- cient physiology is presented to constitute a basis for the facts of health which are discussed. Very extensive use is made of photographs and diagrams illustrating every-day life in the city and in the country. There is at least one interesting and practical original exercise suggested for every principle of health presented in any lesson, and it is the plan that each pupil should work out each exercise and report upon it during the recitation period. In order further to assist the teacher and the pupil, a list of questions, fully covering the text, has been given at the end of each chapter.....