Recognizing the fact that alcoholic drink and tobacco are so disastrous to efficiency in any system of physical training, these instructors rigidly forbid the use of these drugs under all circumstances. While this principle is perhaps more rigorously enforced in training for athletic contests, it applies equally to those who have in view only the maintenance of health. Books on Physical Education. There are many excellent books on physical education, which are easily obtained for reading or for reference. Among these one of the most useful and suggestive is Blackie’s well-known book, “How to Get Strong and how to Stay so.” This little book is full of kindly advice and practical suggestions to those who may wish to begin to practice health exercises at home with inexpensive apparatus. For more advanced work, Lagrange’s “Physiology of Bodily Exercise” and the Introduction to Maclaren’s “Physical Education” may be consulted. A notable article on “Physical Training” by Joseph H. Sears, an Ex-Captain of the Harvard Football Team, may be found in Roosevelt’s “In Sickness and in Health.” Price lists and catalogues of all kinds of gymnastic apparatus are easily obtained on application to firms handling such goods. Various Systems of Physical Exercises. The recent revival of popular interest in physical education has done much to call the attention of the public to the usefulness and importance of a more thorough and systematic use of physical exercises, both at home and in the schools. It is not within the scope of this book to describe the various systems of gymnastic and calisthenic exercises now in common use in this country. For the most part they have been modified and rearranged from other sources, notably from the two great systems, _i.e._, Swedish and German. For a most comprehensive work on the Swedish system, the teacher is referred to the “Swedish System of Educational Gymnastics,” with 264 illustrations, by Baron Nils Posse. There is also a small manual for teachers, called “Handbook of School Gymnastics of the Swedish Systems,” by the same author. Chapter V. Food and Drink. 98. Why we need Food. The body is often compared to a steam-engine in good working order. An engine uses up fuel and water to obtain from them the energy necessary to do its work. So, we consume within our bodies certain nutritious substances to obtain from them the energy necessary for our activities. Just as the energy for the working of the engine is obtained from steam by the combustion of fuel, so the energy possessed by our bodies results from the combustion or oxidation within us of the food we eat. Unless this energy is provided for the body it will have but little power of doing work, and like an engine without steam, must soon become motionless.