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.

99.  Waste and Repair.  A steam-engine from the first stroke of its piston-rod begins to wear out, and before long needs repair.  All work involves waste.  The engine, unless kept in thorough repair, would soon stop.  So with our bodies.  In their living cells chemical changes are constantly going on; energy, on the whole, is running down; complex substances are being broken up into simpler combinations.  So long as life lasts, food must be brought to the tissues, and waste products carried away from them.  It is impossible to move a single muscle, or even to think for one moment, without some minute part of the muscular or brain tissue becoming of no further use in the body.  The transformation of dead matter into living tissue is the ever-present miracle which life presents even in its lowest forms.

In childhood the waste is small, and the amount of food taken is more than sufficient to repair the loss.  Some of the extra food is used in building up the body, especially the muscles.  As we shall learn in Chapter VIII., food is also required to maintain the bodily heat.  Food, then, is necessary for the production of energy, for the repair of the body, for the building up of the tissues, and for the maintenance of bodily heat.