Vitamins

An intensive study of this effect has shown that the actual substance to be activated is not cholesterol itself, but a similar substance known as ergosterol which is found plentifully in ergot of rye and in yeast, but is only present in ordinary choles terol in the proportion of about 1 part in 2,000 (1927, Rosenheim and Webster, Windaus and Hess). When this substance is irradiated with ultra-violet light of wave length, 2,800-3,000 A, a preparation is obtained which is intensely active in the cure and prevention of rickets. Apparently the effect of irradiation on living animals is to produce vitamin D from ergosterol present in small amounts along with cholesterol in the skin. This is absorbed and passes into the general circulation, so that it then acts in the same, still unknown, manner as the vitamin taken by the mouth and absorbed through the walls of the alimentary tract.

Vitamin D can thus be supplied in two entirely different ways, as a constituent of the diet and as a result of irradiation. How much of the ergosterol is converted into vitamin D by irradiation is not known, or indeed whether it is the ergosterol itself or some admixed substance which is the source of the vitamin but the product is highly active in very small doses. Human rickets is rapidly cured by daily doses of 2-4 milligrams, whilst rickets in rats may be cured or prevented by daily doses oft m.o. to 20,00 of a milligram, and the effect of as little as 1.1.000 of a milligram is distinctly perceptible.

The occurrence of vitamin D in food materials is compara tively restricted, the only rich sources apparently being fish-liver oils and the body fat of some fishes. The amounts present in such common articles of daily food as milk and butter are small and are largely determined not by the diet of the animal, but by exposure to irradiation, so that they vary with the season, being less in winter and greater in summer. It is only present in very small proportion, if at all, in green leaves, fruits, etc. Attempts are being made in two different directions to supplement the natural supply of vitamin D in milk and butter. The first con sists in incorporating in margarine, which consists of vegetable fats, a controlled amount of irradiated ergosterol, with the object of making this cheap foodstuff equal to butter as regards vitamin D. At the same time fat from animal livers, or the unsaponifiable matter of such fats, may be added to provide vitamin A. By the second method cod-liver oil is administered to the cow and it is then found (Zilva, Golding and Drummond) that the milk fat is enriched in vitamins A and D.

Vitamin E (the Anti-sterility Vitamin).

The loss of fertility observed in some rats kept on diets freed from vitamins has led to the discovery (1922, Evans and Scott) that a definite vitamin exists, in the absence of which both male and female rats become sterile. This vitamin is fat-soluble like vitamins A and D and can be extracted without loss by ether and other fat solvents from the vegetable tissues in which it occurs (see table below).

Its richest sources are wheat germ and lettuce leaves, but it occurs to some extent in all seeds, in the oils extracted from them, in green leaves, in which its potency is not impaired by desicca tion, and in some fruits. It is also present in animal tissues, chiefly the muscles and the fat, although even in these it only occurs in low concentration. It also occurs in small amounts in egg-yolk and in milk. It is absent from, or only present in very small amounts in, the liver, spleen, kidney, brain and, rather remarkably, the testis. A striking fact is that cod-liver oil is almost entirely free from this vitamin and may indeed be used as a source of vitamins A and D in the basal diet of animals used for experiments with vitamin E. It is also almost completely absent from yeast, from white flour and from polished rice and is present only in small amounts in orange juice. Cooking of fresh tissues, either plant or animal, has no effect on the curative prop erties, but the stability in animal tissues is not so great as in wheat germ oil. The vitamin has been so far concentrated, that a product from wheat-germ oil has been obtained, of which a dose of 5 milligrams on the day of mating is effective in producing fertility.

Vitamins and Diet.

The inclusion of an adequate provision of the various vitamins in the diet is essential for the health of all, but is of particular importance for children and for pregnant and nursing women, since the disturbances due to lack of vitamins in early childhood have far-reaching and often permanent effects on the organism. Not only may the well known deficiency diseases— scurvy, beriberi, pellagra, rickets and xerophthalmia—supervene, but there seems little doubt that the dentition is profoundly affected by the presence or absence in early years of vitamin (1918, Zilva and Wells) and vitamin D (1918, M. Mellanby).