jel'a tin, an animal substance closely resembling glue. It is confined to the solid parts of the body, such as tendons, ligaments, cartilages and bones, and exists nearly pure in the skin, but it is not contained in any healthy animal fluid. Its leading character is the formation of a jelly when its solution in boiling water cools. Gelatin does not exist as such in the animal tissues, but is formed by the action of boiling water. The coarser forms of gelatin, from hoofs and hides, are called glue; that from skin and finer membranes is called size, and the purest gelatin, from the air bladders and other membranes of fish, is called isinglass. Gelatin is a nutritious article of food, and as part of the diet in hospitals it produces the best effects; but animals fed exclusively on it die with the symptoms of starvation, as it cannot yield albumen, fibrin or casein. The combination of tannin with the gelatin in hides changes them to leather, and it is upon this principle that the art of tanning depends. See GLUE; TANNING.