It has already been mentioned that the studies of Kossel, Fischer and of Osborne had made it clear that there should exist very pronounced differences in the value of the proteins from different sources. The proteins were prepared in a state of relative purity and were digested in the laboratory by means of acids, and were analyzed by the methods of Fischer and of Kossel. Certain of the eighteen digestion products, the amino-acids, were determined quantitatively so far as the methods would permit. Although the technique was never perfected so as to give results approximately quantitative, except in the case of less than a third of the amino-acids known to be formed in the digestion of proteins, it was shown in the case of these few amino-acids that there were very great variations in the proportions among them in the mixtures obtained from proteins of different sources. Thus the proteins of the muscle tissues of several species of animals were shown to yield between 12 and 14 per cent of glutamic acid, one of the products of hydrolysis obtained from practically all proteins. The same amino-acid is present in the two principal proteins of the wheat kernel to the extent of about 40 per cent of the total protein content. These two proteins together make about 85 per cent of the total protein of the wheat kernel. Other equally great differences were shown to exist in the composition of proteins of our common food-stuffs, and those of the tissue proteins formed during growth.