Microorganisms for vaccine manufacture are grown under controlled conditions in media which provide the nutrients necessary for growth. Cow components are often used simply because cows are very large animals, commonly used for food, and thus much material is available. Animal-derived products used in vaccine manufacture can include amino acids, glycerol, detergents, gelatin, enzymes and blood. Cow milk is a source of amino acids, and sugars such as galactose. Cow tallow derivatives used in vaccine manufacture include glycerol. Gelatin and some amino acids come from cow bones. Cow skeletal muscle is used to prepare broths used in certain complex media. Many difficult to grow microorganisms and the cells that are used to propagate viruses require | 
