There is no room to doubt that lysin is the limiting factor in this diet, but gliadin furnished decidedly more of this amino-acid than was at the time supposed. Some indication of the nutritive value of the nitrogenous compounds of "protein-free milk" is afforded by experiments carried out by McCollum and Davis (27). They showed that young rats slowly lose weight when confined to a diet in which the entire protein content limited to 1.5 per cent of the food mixture, was derived entirely from skim milk powder. The young rats, however, maintain weight over considerable periods when the amount of milk proteins is increased to 3 per cent of the food mixture. On the other hand, 1.5 per cent of milk protein supplemented with nitrogen equivalent to 1.5 per cent of protein derived from "protein-free milk" served to maintain the animals approximately as well as did 3 per cent from milk powder. From this observation they drew the conclusion that the nitrogen in "protein-free milk" has approximately the same nutritive value as that contained in milk proteins. This would not necessarily be true when it serves as the sole source of nitrogen in the diet, but it is when this product is combined with the proteins of milk in equivalent amount.