Gelatin is a colorless or yellowish, jelly-like animal protein, derived from collagen. Gelatin is obtained by treating animal hides and bones with acid or alkali and boiling them. It dissolves in hot water to form a sol (see colloid) which sets to a gel on cooling. It is used in jellies, soups, and other foods, capsules for pharmaceuticals, photographic emulsion, lithography, and plastics. It has also been used as a source of protein in the treatment of malnutrition, and in bacteriology for preparing culture media.