The problem concerning the ability of the tissues to take a mixture of amino-acids and combine them into proteins for incorporation into living protoplasm, has been studied most adequately by Abderhalden (8). In one of his most suecessful experiments a dog was fed during 100 days upon meat which had been digested to the amino-acid stage (erepton) by the successive action of pepsin, trypsin and erepsin, the protein-digesting enzymes of the stomach, pancreas and intestine, respectively. The digested meat was supplemented with non-nitrogenous nutrients. The animal remained in good health and gained 9.35 kg. in weight. It was demonstrated by such experiments that protein synthesis is possible when the diet furnishes all the essential amino-acids which serve as structural units in the formation of tissue proteins.