It is true that some years ago Slonaker, of Leland Stanford University, in an animal feeding experiment in which one group of rats was fed a mixed diet and the other exclusively on food stuffs of vegetable origin, found that his vegetable feeding rats, although for a few weeks showing themselves superior to the mixed feeders later developed unmistakable evidence of malnutrition and physical inferiority. Some years later, however, McCollum of Johns Hopkins, then of Wisconsin University, demonstrated conclusively that by making a proper selection of vegetable foodstuffs, rats may live and thrive indefinitely on a diet wholly derived from the vegetable kingdom. In connection with this and other similar experiments, McCollum made the interesting discovery that when an animal's bill of fare is to be wholly drawn from the products of plant life it is necessary, in order that the animal shall be fully nourished, that all parts of the plant should be eaten. His experiments demonstrated that if animals are fed upon seeds, alone they undergo physical depreciation, do not obtain full growth, are unable to reproduce or nourish their kind, and ultimately perish. In like manner, roots are found to be incapable of bringing an animal to full development and sustaining its life indefinitely. It was found that to be well nourished the animal must eat in suitable proportions, variable within considerable limits, seeds or fruits and leaves. The great importance of the green leaf as a complement of other foods has been clearly shown. Experiments by McCollum, as well as those of Osborne, Mendel, and numerous other investigators in the same line of research, have made clear several new and highly important facts in the physiology of feeding. They find that foods contain certain subtle elements known as vitamines which are absolutely essential to the full development and prolonged life of an animal. These elements are not found equally distributed in the parts of plants and animals. In seeds they are found chiefly in the outer layers or envelope which is commonly rejected as bran. A certain vitamine especially concerned with growth and development, the fat soluble B, is found in the green leaf along with lime and iron, all of which are deficient in seeds. Roots especially supply an abundance of alkaline salts which are highly necessary to balance up an excess of mineral acids found in seeds.