There have been a number of experiments of short duration giving results which indicate that in the human subject the nitrogen of the potato is of extraordinary value for replacing that lost through daily cata-bolism in the adult (27). McCollum, Simmonds and Parsons (26) have tested this question by comparing with the protein of the cereal grains, the value of the nitrogen of the potato when this tuber was supplemented in such a manner as to make good all its dietary deficiencies, except protein. The experiments involved growth tests in the young rat. The results show beyond doubt that potato nitrogen falls considerably below the value for growth possessed by individual cereal grains, when each of these serves as the sole source of supply of the digestion products of protein.

The experiments which have been reported of the maintenance of rats on potato protein support the conclusion of Rose and Cooper (27), that this nitrogen has a high biological value for the replacement of the tissue substance lost in endogenous metabolism. This observation has a bearing on the question whether the processes of repair can be carried on with certain chemical complexes absent from the diet, which are essential when growth takes place involving the formation of new tissues.