corn, as their protein source in an otherwise complete diet, their health declined and they died. This occurred because zein lacks the essential amino acids lysine and tryptophan. When the researchers added tryptophan to the isolated zein, rats were able to survive but did not grow. When both tryptophan and lysine were added, the rats both survived and grew rapidly. Osborne and Mendel also found that the gliadin, the protein found in wheat was lacking certain amino acids, and that like corn, these deficiencies could be amended by combining grain foods with animal proteins such as eggs or milk. This experiment demonstrated that animals need to acquire certain amino acids from food, which are now referred to as the essential amino acids. In their study of proteins, Osborne and Mendel also aided in the discovery of vitamins. During their feeding trials, they noticed that young rats fed diets with sufficient carbohydrate (in the form of wheat flour) and purified protein, but with vegetable fats or lard instead of butter grew and developed normally for around eighty days, then suddenly began to decline in health and weight then soon died. Many of the animals also developed sore eyes or even ulcers on their eyeballs. Something other than carbohydrates, fats and complete proteins was missing from this artificial diet. When a small amount of butter was added to the feed mixture, the afflicted rats soon recovered completely and continued growing. Whole-milk powder also had the same effect on rat growth. In 1913, the Station's Annual Report stated that “experiments have shown that some still unknown substance is essential to growth and that this unknown substance is present in milk. Much work is being done in an effort to discover an isolate this substance.” As it turns out, this substance was Vitamin A. Concurrently with Osborne and Mendel, Elmer V. McCollum (a former student of Osborne) and Marguerite Davis at the University of Wisconsin were obtaining similar results, and although the scientists submitted their report for publication several weeks prior to the Station scientists, it is clear that both parties discovered vitamins independently. Development of hybrid corn In the early 20th century, Station scientists Edward M. East and Herbert K. Hayes began attempts to improve the quality and yield of corn (Zea mays) through selective breeding and hybridization. In 1906, East realized that steps to prevent self- and close-fertilization made it easier to