Abstract
Soluble calf-skin collagen and other collagenous proteins have been shown to contain a small quantity of non-protein-nitrogen material. The non-protein-nitrogen fraction contained 11 free amino acids which have been estimated quantitatively by the dintrophenylation technique. Three peptides have been isolated as dinitrophenyl derivatives from the non-protein-nitrogen fraction and their amino acid compositions have been determined. The origin of the non-protein-nitrogen fraction is briefly discussed.