The most striking illustration of the value of the nitrogen of "protein-free milk" as a source of amino-acids is seen in its supplementary relation to lactalbumin. The comparative values of casein, edestin and lactalbumin when fed supplemented with this product are shown on page 69. These indicated that lactalbumin was far superior to either of the other proteins for growth. A similar result was observed in experiments designed to show the smallest intake of each of these proteins which would just serve to maintain young rats in weight equilibrium (41). In these experiments diets were employed, having a composition similar to that described in connection with the gliadin studies and containing 28 per cent of "protein-free milk." In some instances, however, but 2 per cent of purified protein were added to the food mixture. In such cases the nitrogen of the purified protein amounted to only 37 per cent of the total, the remaining 63 per cent being derived from the "protein-free milk." In the interpretation of the results no account was taken of this latter increment. Under these experimental conditions lactalbumin appeared to be a protein of extraordinary value.