While the studies with rations restricted to a single plant source were in progress with cattle at the Wisconsin Experiment Station, McCollum, beginning in the year 1907, restricted the diet of rats to each of the more important single grains and seeds, fed as the sole source of nutriment. It was discovered that whole wheat alone, rolled oats alone, maize kernel, or any other seed fed alone, failed to induce any growth in young animals, or to maintain life for a long period of time. It seemed to him in 1913 after the completion of the experimental studies described in this chapter, that he was in possession of the necessary knowledge to enable him to determine the nature of the faults responsible for these failures.