A young animal’s first need is for growth, not having learned to exercise sufficiently to use much energy, and the first food given is an animal product—milk to babes and other mammals, while the young of other animals are first fed upon eggs. The nitrogenous foods are required in smaller bulk than vegetables and fruits; they are more concentrated and contain less waste. According to recent experiments, the average adult requires from two to four ounces a day of nitrogenous foods, to repair the waste, according to the proportion of nitrogen contained. Happily, where more is consumed, the system has the power, up to a certain limit (depending upon the physical condition and the daily activity), to eliminate an excess. It is needless to say that if the daily waste is not re-supplied, the digestion and bodily nutrition suffer. The system _must_ have the two to four ounces to supply the nitrogen daily excreted, or the tissues themselves will be consumed. The proteins, of which meat is the principal one, are classified as Albuminoids:—albumin (white of eggs), casein (curd of milk), myosin (the basis of lean meat and gluten of wheat), Gelatinoids, (connective tissue of meat), Extractives (appetizing and flavoring elements). DIGESTION Any discussion in regard to the digestibility of foods must be general, because food which agrees with one may disagree with another, and a food which disagrees with one at a particular time may entirely agree with him at some other time; therefore, before one passes upon the adaptability of a food to the individual, it should be known that this food agrees or disagrees with him under varying conditions. The digestibility of food depends largely upon the physical condition of the individual, because the amount of digestive juices poured into the alimentary canal is influenced by this condition, particularly by the condition of the nerves. If sufficient juices, in proper proportions, are not poured into the digestive tract, the foodstuffs are not made soluble for absorption into the blood. Digestion is practically synonymous with solution,—all solid foods must be reduced to a liquid state, through digestive juices and water, before they can pass through the walls of the stomach and intestines. Each individual should _learn to like_ the foods containing the nutrient elements which experience and blood tests have shown to be lacking in his case. The question of likes and of dislikes in regard to foods, is largely habit, and one can learn to like almost any food one wishes. Where one forms the habit of discriminating too much in the food, or discarding this food or that, because at some time it has disagreed, due to the particular condition at the time, the mind approaches the table as a more or less pessimistic censor and the saliva and the gastric juices are retarded in their flow.