All foods possess potential or latent energy. The sun is the great positive element, and plants store up the sun’s energy. It is transferred to us through the eating of plants and animal foods. Through the process of oxidation this energy is set free in our bodies, and appears as heat and muscular power. This energy contained in foods is known as heat or fuel value, and is expressed in terms of a heat unit or calorie. A calorie is the amount of heat necessary to raise one kilogram of water, one degree centigrade. This is spoken of as a large calorie, which is used in determining the energy value of food. The small calorie is ¹⁄₁₀₀₀ of a large calorie. The physiological fuel and energy value of the different foods is as follows: 1 gram of Protein yields 4 Calories 1 gram of Fat yields 9 Calories 1 gram of Carbohydrates yields 4 Calories To determine the energy value of a food or combination of foods it is necessary to know first its composition. Then determine the weight of protein, fat, and carbohydrate in grams and multiply these weights accordingly. CHAPTER II. STUDY OF FOODS. The average homekeeper knows little of the nutritive value and chemical composition of the food she buys. The desire to tickle the palate enters more into the selection of food than reason or judgment. Others, who have studied along certain lines without the fundamental training for this work, often make greater mistakes in the selection and combination of foods than if they had not studied the subject at all. It is not sufficient to know just which foods are suitable to the individual and which are harmful; it is necessary to have a fairly well balanced diet which contains the correct proportions of protein and non-protein elements. The following pages present briefs on the value and chemical nature of different foods not mentioned in recipes: VEGETABLE FOODS. These are divided into several classes. They are: Legumes, cereals, roots, bulbs, tubers, leaf, flower and fruit vegetables. All plants are made up of a mass of cells, each consisting of a membranous wall, enclosing a gelatinous mass, in which lie imbedded the nucleus or center of cell activity and minute grains of starch or other material which the plant has manufactured. In young plants these cell walls are called cellulose; later wood cells begin to develop. The wood cells grow into fibrous material, called woody fibre. In poorly grown or stale vegetables this woody tissue becomes very hard and thick, and therefore is indigestible. For this reason it is best that all green vegetables are grown quickly and eaten while they are fresh. When fresh they will snap crisply. Peas, green corn and string beans will cook in one-third of the time if used directly after gathering, instead of being kept for several days before using. THE LEGUMES.