A has been found in all crude fish oils, which have been tested, but cod liver and whale oil appear to be the richest.8

8 Zilva and Miura (Lancet. 1921, I, 323) used a quantitative method of estimation of the fat-eoluble accessory factor in cod-liver oil and butter. It Lard has been generally believed to be entirely lacking in A and for this reason has been regularly used as a component of the basal ration in testing for the presence of A in other foodstuffs, but Daniels and Loughlin** have reported that it actually contains a certain amount, although this is only demonstrable when the lard is fed at a high level (28 per cent). On a diet of 18 per cent of casein (ex-* tracted for 48 hours with ether in a Soxhlet), 28 per cent of lard, 7 per cent of salt mixture, 47 per cent of corn starch, and the water-alcoholic extract of 9 gm. of wheat embryo (previously extracted with ether) they secured good growth and reproduction of rats over a period of 5 months, but when the lard was reduced to 21 per cent growth ceased after about two months. If this is correct, then A is present to some extent at least in all fats of animal origin so far tested but as yet these results lack complete confirmation.

A series of careful investigations has been carried on by Drum-mond * to determine the nutritive value of lard and lard substitutes from the standpoint of vitamins. This work was undertaken in view of the fact that no entirely satisfactory explanation of the deficiency of lard in vitamin content had so far been advanced by any investigator.

In this connection it is appropriate to note the results of some experiments conducted by Drummond on the digestibility of these products. All edible oils and fats with rare exceptions are well digested and absorbed by the mammalian alimentary tract. The following table will show the melting point and digestibility of lard and some of its substitutes was found that the former was much more potent. The high potency is contained particularly in the crude preparations of cod-liver oil.

Steenbock, Sell and Buell call attention to the high content of fat-soluble A in cod liver oil although this oil contains very little yellow pigment. (J. Biol. Chem. 47, 89. 1921).

8aDaniels and Loughlin, J. Biol. Chem. 4a, 360, 1920. 9 Drummond, J. B. C. L 1921, 81 T.

From our present knowledge of the vitamin-content of fats and oils we recognise that the results tabulated above are likely to lead to erroneous conclusions. Judging these fats from the standpoint of their digestibility would place them about on parity. But rating foods on calories and digestion coefficients without considering the vitamin content is no longer sound. Recent researches have demonstrated that the amount of vitamin A present in the body fat of an animal is determined largely by the diet which the animal has received. Apparently the animal organism does not possess the power to synthesize vitamins, but can store up a reserve in certain parts of the body when a surplus is provided in the diet.

In order to throw light on these points, experiments were made with young pigs reared on dietaries some of which were practically devoid of vitamin A while others were supplied with an ample amount of that factor.10

Certain animals from each lot, after several months on the special diets, were slaughtered and samples of leaf fat (peri-nephritic fat) and back fat were removed. By means of the biological method these products were tested for the presence of vitamin A with the following interesting results. The body fats of swine fed on dietaries furnishing ample supplies of vitamin A contained that substance, but its presence could not be demonstrated in the fats derived from animals fed on the foods deficient in vitamin A.

Drummond 11 examined the various processes of lard manufacture in order to ascertain their effect on the vitamin A originally present. The destruction of A at high temperatures was at one time believed to be due to the heating alone,12 but more recently it has been shown that temperatures up to 120° C. do not inactivate the vitamin unless there is contact with air or oxygen. It would, therefore, appear that the destruction is probably due to changes of an oxidative nature.18

The older methods of lard manufacture, which are still used to some extent, are essentially modifications of the original farmhouse process in which the fat is rendered at low temperature, about 70° C, and separated in a simple manner from the connective tissue and water, etc. The more up-to-date processes involve a certain amount of aeration at higher temperatures. Stirring is employed during melting and after the separation of the layers, the fat is stirred at the temperature of 102° C. for ten to fifteen minutes to remove moisture.

10 Drummond, Golding, Zilva and Coward, Biochem. J. 1020, 14, 742.

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

12 Steenbock, Boutwell and Kent, J. Biol. Ghem., 1918, 35, 577; Drummond, Biochem. J. 1919, 13, 81.

13 Hopkins, Biochem. J. 1920, 14, 725; Drummond, Biochem. J. 1920, 14, 734; Zilva, Biochem. J., 1920, 14, 740.

By actual experiment it was found that the lard prepared from hog-fat rich in vitamin A by the simple rendering process contained practically all the vitamin originally present in the fat. However, an active sample of hog-fat was found to have lost practically all of its vitamin A after being converted to lard by the rendering process more commonly used, employing agitation and higher temperatures.

Oleo-stearin also appears to be generally deficient in vitamin A. Beef fat normally contains appreciable quantities of this indispensable dietary constituent,14 and these observers found on crystallisation of beef fat from alcohol that the vitamin is concentrated in the mother liquors together with the glycerides of lower melting point. This explains why in the process of separating oleo-stearin from premier jus the greater part of the vitamin passes through with the expressed oleo oil. The usual process of oleo oil preparation would hardly be likely to affect the amount of vitamin present.