Gelatin (gelatinum) is obtained by acting with boiling water upon certain animal tissues, as the skin, ligaments, and bones, and allowing the solution to dry in the air. It may be obtained in thin, transparent sheets which are permanent if dry, but when moist, readily putrefy. It is soluble in boiling water, and in the proportion of 1 part of gelatin to 50 of water forms a jelly on cooling. In cold water it does not dissolve, though it absorbs water and swells. It is precipitated from solution by tannic acid as a tough, leathery insoluble mass, a matter of importance in the administration of capsules and of gelatin-coated pills. Besides its uses in pharmacy and as a food, a sterilized 1 per cent. solution in amounts up to 100 c.c. per day has been employed by hypodermoclysis and intravenously in hemorrhage and aneurysm to increase the coagulability of the blood. It is a protein food from which indol is not formed, hence has been thought valuable in intestinal putrefaction, but Mendel considers it an inferior food, useless for growth and poor for the maintenance of nutrition. In shock, Hogan uses it intravenously as a colloidal solution that will remain in the vascular system and so maintain the volume of the blood. Any but fresh gelatin is prone to contain putrefactive products or bacteria. Glycerinated gelatin, a compound of equal parts of gelatin and glycerin, is a rubbery mass, used as a basis for vaginal suppositories and urethral bougies. It melts at the temperature of the body.