to secure the greatest possible pleasure and social benefit therefrom and at the same time avoid any injury which ignorance might permit and invite.
It may appear that the inartistic treatment of a subject of this kind, as indicated in the following pages, is not one which is calculated to excite any sympathetic interest or appeal to the natural desire for literary and artistic expression. Yet the importance of the subject is so great as to warrant the experiment of presenting the matter in this form rather than in any more elaborate and connected way.
DEFINITION AND COMPOSITION OF FOODS.
Food, in its general sense, is that which nourishes the body without regard to its physical state, that is, it may be solid, liquid, or gaseous. More particularly defined, food is that material taken into the body in the ordinary process of eating which contains the elements necessary for the growth of tissues, for the repair of the destruction to which the tissues are subjected during the ordinary vital processes and for furnishing heat and energy necessary to life. Incident to the utilization of these elements there is consumed, also, a considerable quantity of matter inextricably mingled with food in a natural way, which takes no direct part in nutrition and yet which is useful, as a mass, in promoting the digestive processes. These bodies are certain indigestible cellular tissues which are present in foods, mineral matter, and other materials which are naturally found in food products. Included in this broad definition, therefore, are many substances which are usually not thought of in the sense of food; among these are water and air. Air, however, would probably be excluded because it is not introduced into the stomach, that is, not in quantities which have any significance in the vital processes. Water, on the contrary, is one of the most indispensable constituents of food and is also used in considerable quantities as a beverage. The water, itself, is indispensable to nutrition and is also one of those bodies mentioned above which are necessary to secure the proper conduct of the digestive processes.
By means of the oxygen in the air the combustion of food in the various parts of the body is secured, and thus animal heat and energy developed. In this respect the combustion of a food product is similar in every way to the burning of coal in the production of heat and motion. The same calorific laws which govern the steam-engine are applicable, in all their rigidity, to the animal engine. The quantity of heat produced by the combustion of a certain amount of fat or sugar is definitely measured in a calorimeter and is found to correspond exactly to the quantity of heat produced by the ordinary combustion of such bodies. The term "food," therefore, in this respect, would include the oxygen of the air without which the development of animal heat and energy would be impossible. It also includes those bodies of a
