Happy is the man whose digestion is so perfect that he is never reminded that he has a stomach. But even those who cannot boast of such enviable powers of digestion, may yet, by a proper amount of exercise and the regulation of their diet, build up health and strength, and lead lives of usefulness and happiness, free from the many ills growing out of improper eating. =Proper Food.=--Life is conditioned upon the proper supply of food. Men may, and do, exist upon very unsuitable food. To be able to do a good day’s work within the hours of a reasonable working day is every man’s birthright. Many men, like Esau of old, sell their birthright for a mess of pottage. Unlike him, however, they are not pressed by stress of hunger, but, merely to please the palate for five minutes, they burden the digestive organs for five hours, and repeat the process day after day. The comparison, therefore, is rather complimentary to Esau. =Constituents of the Body.=--As already remarked, a large part of the human body is water. The body of a man weighing one hundred and fifty pounds contains less than fifty pounds of solid matter. The blood, brain, and nerves are about eighty per cent water; the muscles, nearly eighty per cent; and even the bones and the teeth contain a large percentage of water. Man may be deprived of solid food for a day or more without suffering, and, in some instances, persons have subsisted for several weeks on water alone, but to be deprived of water for ten or twelve hours causes much suffering. The animal and vegetable kingdoms supply the organic substances which constitute a large part of the material commonly known as food, and which sustain the body in life and strength. In addition, various inorganic substances enter into the human structure, prominent among which are salt, lime and iron. Salt is so important to animal life that herds of wild animals have been known to travel many miles to the salt-licks, or springs, in search of it. Some persons, from habit, use it to excess in seasoning their food. Lime and iron are taken into the body through the food. Iron forms about one part in a thousand of human blood. =Classification of Foods.=--For increasing weight and producing heat, the fatty portions of meat, butter, and lard, together with wheat, Indian corn, and sugar, are best adapted; for muscle-making, lean meat, peas, beans, oatmeal; for brain and nerves, shell-fish, lean meats, peas, and beans. Those who lead an active, bustling life, especially if they take an abundance of out-door exercise, will naturally crave strong food in unstinted supply. The busy brain-worker, who is housed all day, and scarcely rises from his chair, needs to be much more careful in his diet. Coarse bread, lean meats, and fruits should constitute his chief dependence, with very limited use of butter, oils, and sugar.