An animal substance soluble in hot water, capable of assuming a we11 known elastic or tremulous consistence by cooling, when the water is not too abundant, and liquefiable again by increasing its temperature. This last property distinguishes it from albumen, which becomes consistent by heat. It is precipitated in an insoluble form by tannin, and it is this action of tannin on gelatin which is the foundation of the art of tanning leather.