Nutritive value of vegetable proteins and its enhancement by admixture.

Introduction It is only since the beginning of the present century that different proteins have been accredited with different nutritive values. Previously, the proteins in a diet represented purely the necessary nitrogenous fraction, and were ‘proteins’ and nothing more. The conception of differing ‘biological values ’ possessed by different proteins was founded on the experimental work of Max Rubner and his assistant Karl Thomas (1909). Their investigations and later those of Mitchell (1923-4) showed the differences existing in the amounts of different proteins which were required to maintain an adult human subject or animal in nitrogenous equilibrium or to support the growth of a young animal. The support of growth in the growing organisms is a more searching test for the nutritive value of a protein than the maintenance of an adult, and this criterion was adopted by Osborne and Mendel in their long series of investigations. (See Osborne, Mendel & Ferry, 1919). By their method the relative nutritive values of different proteins were measured by the weight increase of the experimental animal, usually the young rat, corresponding to the ingestion of a given amount of a protein, which provided the sole source of nitrogen in the diet. The different diets compared contained the same proportion of protein, which was less than the optimum amount in an otherwise complete g. weight increase g. protein ingested’ ration and was thus the factor limiting growth. The ratio, known as