The rupturing of the cells may be accomplished in a variety of ways, as follows: (1) mechanical disintegration, as by grinding in a mortar with sharp sand; (2) freezing the material, by treatment with liquid air, then grinding; (3) killing the cells by drying, by treatment with alcohol or acetone, then grinding the mass in a paint mill with toluene; (4) killing the cells by chemicals (sulfuric acid, 0.5 to 1.0 per cent, or other suitable agents) followed by extraction with water; (5) autolysis, or self-digestion, in which the cells are mixed with toluene or some other antiseptic which kills the cells without injuring the enzymes, then the material is minced or ground up and suspended in water containing the antiseptic, until the enzymes dissolve the cell-walls and so escape into the liquid--this process being especially adapted to the preparation of active extracts from yeasts, which contain the necessary cell-wall dissolving enzymes to facilitate autolysis. Enzymes may be separated out of the aqueous extract obtained from cells ruptured by any of the above methods, by precipitation with alcohol, acetone, or ether, in which they are insoluble; but if this is done, the precipitate must be at once filtered off and rapidly washed and dried, as prolonged contact with these precipitating agents greatly diminishes the activity of most enzymes. Or, they may be adsorbed out of solution on gelatinous, or colloidal, materials, like aluminium hydroxide, or various hydrated clays. If the dry preparations obtained in any of these ways are contaminated by carbohydrates, proteins, etc., these may be removed by treatment with suitable digesting enzymes obtained from the saliva, gastric, and pancreatic juices, and the digested impurities washed out with 60 to 80 per cent alcohol, leaving the enzyme preparation in a purified but still active form.