Chemical and biological studies have been made to determine the nutritive value of certain animal protein concentrates. The commercial digester tankages analyzed varied considerably in content of hot water soluble protein N × 6.25 ranging from 27.3 to 45.8 per cent of the total protein. Commerical meat scraps dry rendered and containing about 50 per cent total protein and reduction tankages to which no “stick” or blood are added are usually lower in hot water soluble protein than digester tankages. Super meat scraps 75 to 80 per cent protein consisting largely of degreased adipose tissue are high in hot water soluble protein 40 per cent of the total protein. Dried whole blood and coagulated blood are low in hot water soluble protein 2.3 to 8.5 per cent of the total protein. As a sole source of protein the hot water soluble fraction of tankages at a 15 per cent protein level is inadequate even for maintenance. The soluble fraction and commercial “stick” have little or no value when used as a supplement to the protein of corn alone, due to a deficiency in the ration of tryptophane and cystine. However, due to their lysine content, these soluble fractions may have some value in supplementing a combination of the proteins of corn and wheat bran. As a sole source of protein at a 15 per cent level, the original tankages and the water insoluble fractions do not support satisfactory growth. As a supplement to corn they are both satisfactory but the insoluble fraction is slightly superior to the original tankage. When used as a supplement to corn and wheat bran, the superiority of the insoluble fraction over the original tankage is less marked. A type of blindness in rats which is different from ophthalmia resulting from vitamin A deficiency, is described. This condition appears to be due solely to tryptophane deficiency. A determination of the amount of hot water soluble protein in tankages is of some help in determining their nutritive value. In conducting experiments to determine the feeding value of animal tankages and meat scraps the type of materials used in their manufacture should be considered.