McCollum wished to answer this "Why?" These experimenters had complied with every known law of nutrition and yet their mixtures failed to nourish the animals. What was lacking? Earlier work at the Station by Professor Babcock suggested an interesting line of attack and in collaboration with Professors Hart and Humphries, McCollum began a series of studies that have become classic contributions to the vitamine hypothesis and brought this worker into the field as one of the most important contributors to the subject. His initial experiments may be briefly summarized as follows: Young heifer calves weighing 350 pounds at the start and as nearly alike in size and vigor as could be obtained were selected as experimental animals. These were divided into groups and fed with rations so made up as to be alike in so far as chemical analysis could determine, but differing in that the sources of the ration were divided between three plants. One group was supplied with a ration obtained entirely from the wheat plant. A second group derived their ration solely from the corn plant. A third from the oat plant and a fourth or control group from a mixture of oat, wheat and corn. By chemical analysis each group received enough of its particular plant to produce exactly the same amount of protein, fat and carbohydrate and all were allowed to eat freely of salt. All groups ate practically the same amount of feed, and digestion tests showed that there was no difference in the digestibility of the different rations. Exercise was provided by allowing them the run of a yard free of all vegetation. It was a year or more before any distinct change appeared in the different groups. At that time the cornfed animals were in fine condition. On the contrary, the wheat-fed group were rough coated, gaunt in appearance and small of girth. The oat-fed group were better off than the wheat-fed but not in so good shape as the corn-fed. In reproduction the corn-fed animals carried their young well. They were carried for the full term and the young after birth were well formed and vigorous. The wheat-fed mothers gave birth to young from three to five weeks before the end of the normal term. The young were either born dead or died within a few hours after birth. All were much under weight. The oat-fed mothers produced their young about two weeks before the normal period. Of four young, so born, one was born dead, two so weak that they died within a day or two and the fourth was only saved by special measures. The young of the oat-fed mothers were of nearly the same size, however, as those of the corn-fed mothers. After the first reproduction period, the mothers were kept on this diet another year and the following year repeated the same process with identical results. During the first milk-producing period the average production per day was 24.03 pounds per day for the corn-fed, 19.38 pounds for the oat-fed, and 8.04 pounds for the wheat-fed. During the second