The carotenoids of butter

data have been collected on the carotene and vitamin A contents of the butter of several breeds of cattle fed under various conditions.In view of the fact, however, that carotene exists in more than one isomeric form [Kuhn and Lederer, 1931; Kuhn and Brockmann, 1933] and that, of these, the a-and y-forms are physiologically only half as active as the f-isomeride [Kuhn, Brockmann et al., 1933] it is obviously important to ascertain precisely in which form the pigment is present in butter.The present paper describes the results of a chromatographic examination of the carotene fractions of a number of ordinary and colostral butter samples with a view to elucidating this problem.The colostral butters, which became available during a larger experiment at present in progress, were especially useful in this investigation on account of their exceedingly high carotene content [cf.Dann, 1933; Semb et al., 1934].The butters (100-500 g.) were saponified as previously described [Gillam et al., 1933] and the unsaponifiable material, after removal of the major part of the