The proper digestion of food depends on the wants of the body, and on its power of appropriating the aliment supplied. The best of food can not be properly digested when it is not needed. All that the system requires will be used, and the rest will be thrown out by the several excreting organs, which thus are frequently overtaxed, and vital forces are wasted. Even food of poor quality may digest well if the demands of the system are urgent. The way to increase digestive power is to increase the demand for food by pure air and exercise of the muscles, quickening the blood, and arousing the whole system to a more rapid and vigorous rate of life. We are now ready to consider intelligently the following general principles in regard to the proper selection of food: Vegetable and animal food are equally healthful if apportioned to the given circumstances. In cold weather, carbonaceous food, such as butter, fats, sugar, molasses, etc., can be used more safely than in warm weather. And they can be used more safely by those who exercise in the open air than by those of confined and sedentary habits. Students who need food with little carbon, and women who live in the house, should always seek coarse bread, fruits, and lean meats, and avoid butter, oils, sugar, and molasses, and articles containing them. Many students and women using little exercise in the open air grow thin and weak, because the vital powers are exhausted in throwing off excess of food, especially of the carbonaceous. The liver is especially taxed in such cases, being unable to remove all the excess of carbonaceous matter from the blood, and thus “biliousness” ensues, particularly on the approach of warm weather, when the air brings less oxygen than in cold. It is found, by experiment, that the supply of gastric juice, furnished from the blood by the arteries of the stomach, is proportioned, not to the amount of food put into the stomach, but to the wants of the body; so that it is possible to put much more into the stomach than can be digested. To guide and regulate in this matter, the sensation called _hunger_ is provided. In a healthy state of the body, as soon as the blood has lost its nutritive supplies, the craving of hunger is felt, and then, if the food is suitable, and is taken in the proper manner, this sensation ceases as soon as the stomach has received enough to supply the wants of the system. But our benevolent Creator, in this as in our other duties, has connected enjoyment with the operation needful to sustain our bodies. In addition to the allaying of hunger, the gratification of the palate is secured by the immense variety of food, some articles of which are far more agreeable than others.