The examination of yeast-fat for the presence of vitamins A and D before irradiation and of vitamin D after irradiation

IN 1924, one of the writers (I.S.-M.) with E. M. Luce carried out some experi- ments on rats in which the effect of the addition of yeast-fat to a diet de- ficient in the fat-soluble vitamins was tested [1925]. At the time at which this work was undertaken it was not generally recognised that the fat-soluble vitamin factor contained two components. Although this view was originally brought forward in 1922 by McCollum, Simmonds, Becker and Shipley [1922], it was not till after the publication of a paper by Steenbock and Nelson [1924] that the presence of two distinct vitamins in cod-liver oil was clearly estab- lished; a deficiency of one of these (A) was shown to be responsible for the symptoms of ophthalmia and a deficiency of the other (D) was correlated with defective calcification of the bones, while both were able by their absence to limit growth. Since 1924, it has been clearly recognised that both vitamins A and D are present in cod-liver oil but that only the effect of the D vitamin can be replaced by irradiation of the animal. The results obtained by Luce and Smedley-MacLean showed that the addition of yeast-fat to a diet deficient in the fat-soluble vitamins resulted both in increased growth and in increased calcification of the bones; they attributed these results to the presence of the fat-soluble vitamin A in the yeast-fat since at that time the vitamins A and D were not differentiated. In the light of present knowledge the results then obtained would be interpreted as indicating the presence of vitamin D in the unirradiated yeast-fat and as yielding no information as to the presence or absence of vitamin A. The influence of yeast-fat in promoting growth con- firmed the conclusions previously drawn by Hopkins [1912] from his experiments in which a marked effect on growth was obtained by the addition of the ether-soluble extract of yeast to a diet deficient in the fat-soluble vitamins. It seemed therefore of interest to repeat the work of Luce and Smedley-MacLean and to extend it to a separate examination for the two vitamins A and D which improved technique has now made possible.