» Antivenin (Crotalidae) Polyvalent conforms to the regulations of the FDA concerning biologics (see Biologics 1041). It is a sterile, non-pyrogenic preparation derived by drying a frozen solution of specific venom-neutralizing globulins obtained from the serum of healthy horses immunized against venoms of four species of pit vipers, Crotalus atrox, Crotalus adamanteus, Crotalus durissus terrificus, and Bothrops atrox (Fam. Crotalidae). It is standardized by biological assay on mice, in terms of one dose of antivenin neutralizing the venoms in not less than the number of mouse LD50 stated, of Crotalus atrox (Western diamondback), 180; Crotalus durissus terrificus (South American rattlesnake), 1320; and Bothrops atrox (South American fer-de-lance), 780. It may contain a suitable preservative. When constituted as specified in the labeling, it is opalescent and contains not more than 20.0 percent of solids, determined by drying 1 mL at 105 to constant weight (±1 mg).