Things are commonly measured by volume, or by weight. That volume could not be made sufficiently accurate in the measurement of food values is evident. A bushel of lettuce leaves would contain much less food value than a bushel of wheat. Weight would seem to be a fairer way to compare foods, but all foods contain water, which may vary from five to ninety-five per cent. A pound of turnips, which is nine-tenths water, would not be comparable with sugar, which has scarcely any water. Even if it were not for the water, weight would not be a fair method of comparison because some foods are of more value per pound than others, owing to their difference in chemical composition. For instance, a pound of butter gives about two and one-fourth times as much heat to the body as sugar. As before mentioned, the two chief food factors which we ought to measure are energy-producing and tissue-building power. [Sidenote: What constitutes a true food] All true foods when assimilated in the body produce some energy. In fact, only such substances as produce bodily energy, when combined with the oxygen taken in through the lungs, can be correctly termed food. I have taken this energy-producing power of food as the best basis for measurement and comparison. The nitrogen could have been taken as a unit, and the energy figured by a table, but it is simpler to use energy as a unit (as given in column 3, p. 655), and figure the nitrogen in the various foods by means of a table which gives the amount of nitrogen per unit of energy. (Column 4, p. 655.) Multiplication of units of energy (column 3) by the nitrogen factor (column 4) is necessary because the ratio of nitrogen to energy is different in each food. EXPLANATION OF TABLE In the table that follows, I have attempted to give in the simplest way the amount of each particular food that one vieno equals. The second column shows, in the plainest language possible, what one vieno of food equals--as, one vieno of barley equals one ounce; or, one vieno of nuts equals one rounded tablespoonful, etc. This method is, of course, only approximate, as in some foods it is impossible to find a simple term to express the amount of one vieno. This is especially true of cooked foods because of the varied amounts of water contained. In such cases the way for the student to become familiar with a vieno is to weigh one pound of the raw material, and, after it is cooked, weigh it again, and then calculate the water content. The definition given in the second column in the case of milk, butter, eggs, and cheese is fairly accurate. The description given in the case of cereals and bread is also fairly accurate. In the list of fresh vegetables, no attempt has been made to describe one vieno by volume, as, vegetables being loose and bulky, it is practical to measure them only by weight. [Sidenote: Only the edible portion of food considered]