It was pointed out in 1917 by McCollum, Simmonds and Pitz (3) that the alfalfa leaf is several times richer in fat-soluble A than are such grains as wheat, maize or oat kernel. This line of investigation has been furthered by Osborne and Mendel (4), who have found spinach, alfalfa leaves and clover leaves, to be relatively rich in both fat-soluble A and water-soluble B. Ten per cent of one of these leaves in a diet which derived its sole content of fat-soluble A therefrom, proved an adequate source of this dietary essential for the promotion of fairly rapid growth during periods up to 170 days. Timothy proved somewhat less valuable for this purpose. These results show clearly that these leaves are excellent sources of this vitamin. Cabbage, a thick leaf, specialized as a storage organ, was distinctly poorer in both the uncharacterized essentials under consideration than were thin leaves.

Steenbock and Gross (5) extended these studies and found that 5 per cent of immature alfalfa leaf in the diet as the sole source of the fat-soluble A, the remainder of the diet being satisfactorily constituted, sufficed to support normal growth, and allowed the rearing of some young. Lettuce, spinach and chard contain fat-soluble A in similar amounts, but lettuce appeared to be somewhat poorer than the other leaves studied. Cabbage was found to be deficient, in comparison with other leaves, in its content of fat-soluble A. These investigators repeatedly emphasized their conviction that the substance fat-soluble A is intimately associated with yellow pigmentation. Those leaves which contained much yellow pigment, although masked by the green pigment chlorophyll, were richer than cabbage, which contains little yellow pigment.