Of the unidentified fat-soluble and water-soluble substances essential to normal metabolism we have as yet no direct quantitative measures, either of the proportions in which they occur in food or are needed in nutrition. In view of their importance it is plain that they should not be ignored in the planning of dietaries, either of children or adults. McCollum and Sim-monds have recently shown that a low intake of either "fat soluble A" or "water soluble B" not only retards or suspends the growth of young animals but is also distinctly detrimental to adults. A diet furnishing barely enough of these essentials to support slow growth of young regularly resulted in subnormal vitality when fed to adults; but the symptoms were not always the same, e.g. some of the adults lost weight while others maintained weight but lost vitality. They state: "Our results indicate that there is no low plane of intake of either of these substances which can be said to maintain an animal without loss of vitality. When the minimal amount necessary for the prevention of loss of weight is approached, the life of the animal is jeopardized if the diet is persisted in." They also find that "the animal can tolerate being limited to a very low intake of either the dietary A or B much better with an otherwise excellent diet than when it is less well constituted," and also that "it is better to have a liberal supply of one and a minimal supply of the other of the A and B than the minimal allowance of both." The presence of sufficient quantities of these substances is insured by making prominent in the diet the types of foods rich in them. These are chiefly: milk and its products, eggs, vegetables, fruits, and the outer portions of the cereal grains - all foods which it is wise to make prominent in the diet for other reasons as well. It will be remembered that "fat soluble A" and "water soluble B" may or may not occur abundantly in the same articles of food. Milk, eggs, and green vegetables appear to be rich in both; butter in "fat soluble A" and whole grains in "water soluble B." Thus either milk or eggs alone, or both butter and whole grain products, would provide the two kinds of unidentified essentials. When both economy and efficiency are considered, it appears that milk and vegetables are especially worthy of a more prominent place in the diet than is commonly given them in present American practice.

* In the case of the child this should be mainly milk protein.