McCollum sought to compare in growth value the proteins of wheat, maize and oat kernels in young swine. He confined the animals in metabolism cages, thus making possible the collection of the excreta during a period of thirty to sixty days, during which the animals were fed exclusively on a single grain and water (56). From the record of the nitrogen intake and output of the animals he calculated the amount of protein of the food which was converted into tissue proteins for new growth. The results indicated that the protein mixture contained in each of these grains can be utilized to about the same extent. The nitrogen of the proteins retained amounted to between 20 and 26 per cent of the amount ingested in all cases. The per cent of protein in the food did not appear to influence the extent of utilization.

It is now certain that the diet used in these experiments was faulty, in respect to the unsuitability of the mineral content of these grains for the maintenance of prolonged normal development. The grains are deficient in fat-soluble A, and are almost entirely lacking in the anti-scorbutic factor water-soluble C. The pig is susceptible to scurvy, and the lack of the latter was perhaps a factor of importance in determining the outcome of the experiments. The two first named essentials certainly influenced the result of these studies, for the rate of nitrogen retention fell off toward the end of the period of observation.