On the publication of the paper in which these experimental results were described in 1909, it appeared to be established that the long accepted views concerning what the diet must contain in order to be adequate, were correct, and that the chemical methods for the analysis of foods actually afforded data from which the nutritive properties of a diet could be appraised. The data also seemed effectually to dispose of the disputed question concerning the relative merits of phosphorized as compared with phosphorus-free proteins, and indeed, could be interpreted only to mean that the animal body is capable of synthesizing from salts of inorganic phosphoric acid, all the complex phosphorus-containing organic substances which are so important as components of living matter.

These ideas being accepted as proven facts, it seemed that the next great advance in the field of nutrition investigations was in the field of study of the relative values of the numerous proteins of the plant and animal tissues, which organic chemists had been recently studying by improved methods, and which they showed to be very differently constituted when derived from different sources. The chemical methods were not entirely satisfactory for the analysis of these complex bodies. Even in the hands of the most skilled chemists, among whom Kossel, Fischer, and Aberhalden in Germany and Osborne in America were the most noted, only a little more than half of the protein molecule could be accounted for in the form of identifiable products of digestion, the amino-acids. Obviously such analyses, although representing a marked advance in chemical science, were too incomplete to permit of using them as a basis of judgment as to the nutritive values of individual proteins. The way now seemed open, however, for the quantitative comparison of individual proteins, carefully isolated and purified, by feeding a single protein as the sole source of this dietary factor, and with a diet which was otherwise complete and satisfactory. A series of such experiments in which proteins from various sources were employed, should reveal differences in their values for transformation into body proteins during growth. The experimental studies of Mc-Collum, just discussed, seemed to make such investigations possible. In 1909 Osborne and Mendel undertook to carry out such a series of researches on purified proteins. Osborne had for many years made a thorough study of the number and nature of the proteins in various cereals, legume seeds, nuts, oil seeds and of certain animal tissue proteins, and possessed the knowledge, skill and equipment for their preparation on a large scale.