There is a difference between the cultivated and the normal appetite. A child rarely shows a desire for stimulants or condiments, unless unwisely encouraged by an adult, who does it,—_not because it is good for the child, but because the individual himself has cultivated a taste for it_. It is as easy to form healthful tastes and habits of eating as unhealthful ones, and care should especially be exercised in the formation of healthful habits by the growing child. The simple foods, in their natural state, are in the right condition to be digested, with the aid of heat to break the cellular coverings of the globules of some of them, but time, energy, muscular activity, nerve force, and money are spent in combining, seasoning, and cooking foods in such a manner as often to render them difficult of digestion. _Deep breathing of fresh air, to throw off the poisonous carbon dioxid and to supply an abundance of oxygen to oxidize the waste, thus putting it in condition to be expelled from the system; brisk exercise to accelerate the circulation, that the blood may carry the oxygen freely and that the tissues may liberate the carbon dioxid and other waste; and a copious drinking of water, are the best tonics for loss of appetite or for a lack of vitality._ * * * * * [Sidenote: Economy in Food] It is economy, therefore, to keep the digestive organs and the circulation and tissues strong, in order that all foods eaten may yield returns, instead of hampering activity. The food which furnishes the most tissue-building substance and yields the most heat and energy, with the least refuse, is the economical food. In the selection of food for any individual, the result to be gained from the food must be borne in mind. If one is doing heavy muscular work, more protein to rebuild tissue, as well as more carbohydrates and fats to produce energy, are required than if one’s habits of work are sedentary. In mental work, where the brain is continually active, proteins are required to re-supply the brain tissue, but the fats and carbohydrates may be lessened. This would seem to contradict the theory that where one’s habits are sedentary and the brain alone is active, the proteins are not required. In sedentary occupation, the carbohydrates and fats are stored within the system, clogging it and producing torpid liver, constipation, and obesity,—unless the brain is sufficiently active to use all of the fuel in brain energy.