_Per cent._ Oxygen, about 65 Carbon, about 18 Hydrogen, about 10 Nitrogen, about 3 Calcium, about 2 Phosphorus, about 1 Potassium, about 0.35 Sulphur, about 0.25 Sodium, about 0.15 Chlorine, about 0.15 Magnesium, about 0.05 Iron, about 0.004 Iodine } very Fluorine } minute Silicon } traces As the actual composition of the body is changing day by day, through the activities of the system, so that it is commonly believed that after some years all the tissues are entirely renewed, the daily wear and tear, as also the material expended in heat and activity, must be supplied by the diet. For the ordinary requirements of the system, in health, the appetite serves as a guide, which should suffice in man as in wild animals, to preserve the balance of nutrition. But man has also the power to _gratify the taste_, which must be recognized in our study as distinct from the satisfying of the appetite; and the refinements of civilization have added so greatly to the temptation of wrong and over-eating and drinking, as they have to many other temptations, that it is questionable if reason, and what is often spoken of as the natural instinct for food, can be trusted in mankind.