=The standard portion.=——Knowing the composition of any food material, it is possible from these figures to calculate the total fuel value, or we can refer to tables in which this has been calculated, and save ourselves labor. For comparison of different foods the Standard, or 100-Calorie, Portion is used, as this corresponds very closely with the amount of food for a single serving in many cases. In the sections treating of different foods the Standard Portion will be stated. =Food for body building.=——Every living cell has a little life history of its own, and constantly demands a certain amount of new material to replace old which it has worn out. Besides this, old cells die, and new ones have to be made to replace them. Hence even a full-grown person needs building material, and much more is required in proportion when the person is growing and perhaps adding several ounces a week to his weight. The foodstuffs which have especial value as building material are protein and mineral matter. =Food for body regulating.=——To help in the digestion of food, to keep the blood in proper condition, the muscles supple, and all the processes of the body at their best, ash constituents and water in the diet are necessary. A tabular summary of the functions of the foodstuffs and an outline of the changes which take place in digestion will be found in the appendix. We are now able to give a more complete answer to our question, “What is Food?” Food has been said to be that which taken into the body builds tissue or yields energy, or both. The food as a whole must contain all the chemical elements needed by the body, these elements being supplied in substances known as foodstuffs, viz., protein, fat, carbohydrates, mineral matter or ash, water. To be a food, a substance must contain one or all of the foodstuffs. It must be noted here that our food materials as bought, contain inedible matter, as in the shells of eggs, the bone of meat, the skins and pods of vegetables. Moreover, the fiber that we eat in vegetable foods is not digested under ordinary circumstances, but seems rather to serve a useful purpose in giving bulk to our foods. =Food adjuncts.=——In preparing foods for the table, we have the habit of adding substances to develop or give flavor. With the exception of sugar, which we use largely for its agreeable taste, these substances have no nutritive value. They are not hurtful unless used in excess, although pepper and other spices sometimes disturb digestion. Pepper, too, irritates a delicate throat. Only a few flavors are really detected by the sense of taste. These are salt, sugar, acids, and bitter flavors; and something in the spices that gives a sensation hard to describe, but is unmistakable in an overdose of mustard or horse-radish. “Pungent” describes such a flavor.