Most seeds contain some vitamin A, but very few are rich in this factor.25a Flax and millet seeds and the Georgia velvet bean have an exceptionally high content of A, but the ordinary edible seeds contain relatively little.26 Coward and Drummond 27 found that nuts such as the Brazil nut, peanut, walnut, and almond, furnish only an insignificant amount of A despite their high fat content.

22 Steenbock and Gross, J. Biol. Chem. 41, 149, 1020.

23 McCollum, Simmonds and Parsons, J. Biol. Chem. 36, 197, 1918.

24 Steenbock and Gross, J. Biol. Chem. 40, 501, 1919.

25 See also Steenbock and Gross, Ibid. 40, 529, 1919, and Osborne and Mendel, Ibid. 41, 555, 1920.

25a White rats fed rations in which all the protein (18.4%) was supplied by tomato-seed press cake grew at the normal rate. Water-soluble B and fat-soluble A vitamins apparently were furnished in adequate amounts for normal growth when one-half the ration consisted of tomato-seed cake, the other half being made up of purified products. Finks and Johns, Am. J. Physiol. 56, 404, 1921.

Fruits have not been very extensively investigated as to their content of A, but bananas contain at least some of this vitamin, while lemons, grape fruit and oranges are apparently completely lacking. Tomatoes are unusually rich in A, dried tomato being more efficient, weight for weight, than butter-fat.

Various factors influence the value of milk and butter as sources of vitamin A. Drummond, Coward and Watson28 have studied these variations. The diet of the cow is undoubtedly the chief cause of variations in the amount of vitamin A in milk. Colostrum is richer than milk; butter is somewhat poorer, partly owing to mechanical loss and partly to destruction. " Blowing " and other methods of butter-making which involve exposure to air at high temperatures, may cause a loss of vitamin A. The vitamin content of butter produced in winter is low, sometimes very low, because the cattle are stall-fed on dry feeds of hay, roots and cake; even a summer drought may lower the vitamin content. Storage of butter does not lower the vitamin A content unless there is oxidation, nor does development of rancidity per se. "Renovation " of rancid butter will entail further loss of vitamin, if the methods employed cause oxidation.

Stammers reports that bran contains vitamin B and also some vitamin A.

McCollum and others have endeavored to correlate the distribution of vitamins with the function of the plant organ.80 It has been found that the leaf of the plant is several times richer in fat-soluble A than are the wheat, oat, and corn kernels. Certain seeds approximate the value of the leaf in this substance. Hemp seed is distinctly better than those just named, but flaxseed and millet seed are still richer than hemp seed and may readily be incorporated in the diet in amount sufficient to meet the needs of an animal for the fat-soluble A during growth.

26 A series of careful feeding tests conducted by Sure and Read has established the fact that the Georgia velvet bean seed of early speckled variety is abundant in fat-soluble A but low in water-soluble B. This seed when fed raw is injurious to the growth of young rats. However, the injurious effect can be destroyed to a great extent by autoclaving the seed for one hour at 15 pounds pressure without destroying the vitamins. (J. Agricultural Research, aa, No. 1, 1021). According to Finks and Johns (Am. J. Physiol. 57, 61, 1921) the nutritive value of the proteins from Chinese and Georgia velvet beans is not satisfactory.

27 Coward and Drummond, Bioch. J. 14, 665, 1920.

28 Drummond, Coward and Watson, Biochem. J., 1921, 15, 540, 1921.

29Stammers, Biochem. J. 15, 489, 1921.

30 McCollum, Simmonds and Pitx, J. Biol. Ghem. 30, 18, 1917.

It is interesting to note that the content of the fat-soluble A is highest in those seeds which are smallest (flax and millet). Possibly this may be in some measure related to the relatively large proportion of germ as compared with endosperm in such seeds. The endosperm is in great part to be likened to a mixture of purified proteins, carbohydrates, and fats, while the germ is relatively rich in functioning plant cells as well as fats, carbohydrates, etc. The differences in the amount of stored food material contained in the germ in various seeds render it impossible to make such a comparison very accurate. It has been suggested that the differences in the dietary properties of the entire seed as contrasted with the embryo, and of polished rice as contrasted with hulled rice, may lie in part in the association of A and B with the functioning cell. In like manner, it is possible to account for the exceptional richness of the leaf in these two dietary principles. The leaf is the seat of great synthetic activity and comprises a relatively large amount of functioning cells associated with those substances which may be considered as the equivalent of purified protein, carbohydrate, and fats.

This point of view is criticized by Steenbock and Gross31 who point to the great variation in vitamin content of organs so closely associated in function as tubers and roots. These investigators have adopted a hypothesis of their own, according to which A is associated with the occurrence of certain yellow plant pigments. In support of this hypothesis it is pointed out32 that experiments with eight varieties of corn have indicated that white corn contains practically no fat-soluble vitamin while yellow corn contains a sufficient amount to permit normal growth and reproduction in the rat. Colored roots such as carrots and sweet potatoes have been found to contain much fat-soluble vitamin, while the uncolored sugar beets, mangels, dash-eens and Irish potatoes show little of it. Experiments with commercial oleo oils show that those most highly pigmented are also richest in fat-soluble vitamin, while the least pigmented are poorest in this growth essential. The fact that the yellow pigment in butter-fat disappears simultaneously with the destruction of the vitamin by heating may or may not be significant, but is at least a suggestive coincidence.32a The occurrence of certain materials which contain as much fat-soluble vitamin as yellow corn, but which are much less pigmented might be due to the presence of a leuco compound of the yellow pigment.33

31 Steenbock and Gross, J. Biol. Chem. 40, 503; 41, 149. See also Steenbock and BoutweU, J. Biol. Chem. 41, 81,163; 4a,131. Steenbock, Sell, Nelson, and Bnell, Proe. Soc. Biol. Chem. J. Biol. Chem. 46, xxxii, 1921. Steenbock, Sell, and Buell, J. Biol. Chem. 47, 89, 1921.

32 Steenbock, Science, 60, 3S2, 1919.

32a In beef-fat and butter-fat, according to Stecnbock, Sell and Buell, the content of A does not closely parallel the pigment content. However, both vitamin and pigment are closely associated in these fats and hence the most highly pigmented fats are generally richest in vitamin A. (Steenbock, Sell and Buell, J. Biol. Chem. 47, 89, 1921).

33 Willaman (Am. Food Jour., Oct. 1921) emphasizes the virtues of yellow vegetables based on the observations that yellow color and vitamin A practically alwayB occur in parallel amounts. The list includes sweet potato, Irish potato, mangel, squash, dasheen, sugar beet, many varieties of corn and peas, spinach, chard, lettuce, cabbage, alfalfa, clover, timothy and tomato fruits.