The study by many scientists during the past few years of the enzymes and their striking specificity; of the salts; of the insufficiency of many proteins, and of the vitamins is epoch making, and has caused a corresponding advance in dietetics. These discoveries are so important as to raise the question whether nutritive failure or success does not depend as much on the accessory bodies—the vitamins, the enzymes, and lipoids—as on the primary element of the diet. In addition to these food principles, there exists in our food a number of compounds which, while not indispensable, act beneficially as flavorings, stimulants to digestion, etc.; these are termed food adjuncts, and comprise such bases as caffein, essential oils, organic acids, etc. =Standard Dietaries: The Maintenance Diet.=—There is great need of _standardization_ and of knowledge regarding the maintenance diet, first among physicians and then among the people in general, or scientific dietaries based on the nutritive value of foods. These are given in terms of proteins, carbohydrates, and fats, together with the aggregate energy of the nutritive value in each. This is the corner-stone of dietetics. _Dietetics_ is the science of feeding. It has to do with the necessities of the body and the ability of the food to meet these necessities in the various circumstances and conditions of life. The ultimate scientific knowledge concerning human nutrition should be to promote the healthful and economic use of food. The problems to be dealt with are quite complex. These are: (1) changes in the economic conditions of the population; (2) changes in food production and food supply; (3) changes in the methods of preparing food. In regard to the influence of the economic conditions of the people on the composition of their diet, it might be expected that a considerable decrease in the earning capacity of the poorer people, or an increase in the cost of foods, would be followed by a change in their diet. Everyday experience teaches that under such conditions the more expensive foods—meat, eggs, and milk—are reduced in the diet. These same foods are also rich in vitamins, so that a reduction here would, therefore, reduce the vitamin content of the dietary unless other dietary complements rich in vitamins, such as legumes, were introduced. The value of any food as a source of heat and energy is measured by a bomb-calorimeter. The heat given off during the combustion is a measure of the latent or potential energy of the food. The kinetic energy of the food is the amount of heat developed by the proportion which is digested. The unit commonly used is the calorie, or the amount of heat which would be required to raise the temperature of 1 kilogram of water 1° C., which is about equal to that required to raise the temperature of 1 pound of water 4° F.