Considerable variations in the vitamin content of oleo oil may be encountered, but these are in all probability due to the seasonal variations in the diets of the animals. Oleo-stearin is practically always of low vitamin value. The nutritive value of compound lard will therefore be much influenced by the vitamin content of the constituents employed in its compounding.15

Lean meat and fish are probably entirely deficient in ii.l5a.

Vegetable fats and oils seem in general to be poor in A, although as Drummond points out,16 no hard and fast line can be drawn between these two classes of oils and fats when their value as sources of the fat-soluble vitamin A is considered. Certain vegetable oils, as for example palm and yellow maise oils, are in the crude condition good sources of the vitamin. Both animal and vegetable oils and fats tend to lose vitamin A on refining. Bolton observes that it would be desirable to find a method whereby the manufacturer could first separate the vitamins from oils, then carry on the refining process, and re-introduce the vitamins which otherwise would be destroyed by the process.17

14 Osborne and Mendel, J. Biol. Chem., 1915, so, 379.

15 Drummond, J. 8. C. I. 1921, 81T.

15a In rats, dead as a result of vitamin-free diets, both fats and lipoids may be completely lacking in the " lipoid gland tissue." It is suggested by Cramer (Proo. Physiol. Soe.; J. Physiol. 54, ii, 1920) that this lipoid gland tissue forms an important deposit of one or more of the vitamins is Drummond and Coward, Bioch. J. 14, 668, 1920.

16J. 8. C. I. 1921, 81 T.

Comparing the different plant structures, the leaves are undoubtedly richest and the seeds as a general rule poorest in A, although flax and millet seed appear to be an exception.

Of the leaves which are used for human food, spinach seems to be the most efficient. Steenbock and Gross18 found that five per cent of lettuce, spinach, and chard in the basal ration furnished enough A for long continued though somewhat subnormal growth. Few young were produced and none were reared but in no case was there any appearance of the xerophathalmia commonly associated with deficiency of A. Judging by the appearance of the animals, spinach seemed to be the most satisfactory and lettuce the poorest, of this group. Osborne and Mendel19 also noted that spinach leaves appeared to be richer in A than most of the products used in an ordinary diet.

The grasses clover, alfalfa, and timothy have all been found exceptionally rich in A, especially when cut before reaching full maturity and carefully cured. Steenbock and Gross20 found it possible to secure growth at the normal rate on a ration carrying five per cent of alfalfa as the only source of A. Young were successfully reared, although the time for rearing was prolonged eight to ten days beyond the normal, thus giving indisputable evidence of the richness of alfalfa in the fat-soluble vitamin. How much less than five per cent of the ration might have been constituted of alfalfa and still have produced results such as the above was not determined, but Steenbock and Oross were inclined to think from the curves of growth and the behavior of the young that they had reached approximately the lowest level possible with their material. With five per cent of clover as the source of A, growth approximating normal was secured, and young were reared though at a subnormal rate of growth.

Osborne and Mendel tested the value of various plant and animal products21 by determining the amount necessary to promote renewed growth in rats which had declined on a diet deficient in A but suitable in all other respects. Their basal ration was composed of meat residue, 19.6 per cent, salt mixture of 4.0 per cent, starch 52 per cent, lard 24 per cent, and yeast 0.4 gm. daily. On such a diet, rats soon fail to grow and then begin to decline rapidly in body weight, but unless the damage has been allowed to go too far, restoration to health and renewed growth can be brought about by replacing part of the lard by butter-fat or some other potent source of A. When the other dietary factors were satisfactory they found 0.5 gm. of butter-fat (five per cent of the ration) sufficient for this purpose, but made no tests to determine whether this amount represents the minimum. The superior efficiency of some plant products as a carrier of the A vitamin is indicated by the fact that as little as from 25-70 mg. per day of ether extract of clover, timothy, alfalfa or spinach induced recovery and rapid growth in animals which were suffering from lack of this vitamin.

A similar amount of dried cabbage was not sufficient, although there was evidence of the presence of some A. Steenbock and Gross 22 were not very successful in attempting to use fresh cabbage as a source of A, owing to the fact that cabbage is liable to cause digestive disturbances which result in a decreased food intake and consequent complications in the relation between growth and diet. Fifteen per cent of cabbage in the ration was sufficient to prevent decline and even to promote growth, though at a subnormal rate, but the fact that addition of butter-fat produced prompt acceleration in the rate of growth indicated that this amount of cabbage did not furnish the optimum amount of A.

18 Steenbock and Gross, J. Biol. Chem. 41, 149, 1920.

19 Osborne and Mendel, J. Biol. Chem. 37, 188, 1919.

20 Steenbock and Gross, J. Biol. Chem. 41, 149, 1920. 21 Osborne and Mendel, J. Biol. Chem. 41, 661, 1920.

Tubers and roots differ considerably, but may be regarded for the most part as intermediate between leaf and seed. White potatoes are not rich in the factor, being about equal to the cereal grains in this respect, according to McCollum, Simmonds and Parsons," while the sweet potato has a much higher concentration of A, 15 per cent in the diet being sufficient to permit of normal growth and reproduction. Carrots are about equivalent to sweet potatoes as a source of A, but the dasheen, which is a vegetable of very similar type, is apparently almost devoid of it,24 and the sugar beet and mangel contain very little.25