“=Something Unknown.=”—Recent investigations by Dr. F. G. Hopkins, of Cambridge, England, and Dr. E. V. McCollum, formerly of Wisconsin, now of the Johns Hopkins University, have proven conclusively that one food ingredient cannot always be substituted for another with impunity even though the most searching chemical analysis shows them both alike in contents and digestibility. There is “Something Unknown” in certain foods—“Vitamines” some call it—essential especially in promoting the growth of the young, which our present knowledge of chemistry cannot explain. In Bulletin No. 17 of the Wisconsin Experiment Station experiments with the feeding of rats are described which show how butter-fat could not be replaced in the ration by vegetable fats of apparently the same composition and digestibility without disastrous results, and similar conditions have been found in regard to other foodstuffs, proteins as well as fats. The yolk of eggs and butter-fat contain this unknown something which is absolutely essential for the growth of the child and which is missing in most substitutes, especially in lard and vegetable fats. [Illustration: The rat on the left got five per cent of cottonseed oil and the one on the right got instead one and a half per cent of butter-fat, otherwise their rations were alike. These results are typical for any ration made up of purified foodstuffs with butter-fat in them as compared with any fat of plant origin. The plant fats lack an unknown something without which growth cannot proceed. ] The above illustration is from the work of McCollum and Davis at the Wisconsin Experiment Station. Realizing the fallacy of the old rules for making up rations for the feeding of farm animals, Professor Evvard of Iowa is trying the _reliability_ of the _instincts_ of animals as a guide to the proper selection of the most favorable combinations and proportions of food ingredients.[10] We mention these experiments as a warning against placing too great reliance on the caloric theory or the relation of nutrients in making up food rations. We have yet much to learn and the good housewife trying to cook according to scientific rules will do well not to neglect the palatability of the food, but to watch the “instinct” which causes the child or the adult to reject or approve of, and enjoy, the food, which in most cases is a better guide than calories or protein contents, or the ration between the various groups of nutrients. CARE OF MILK IN THE HOME