611. Testa.—Oyster Shell.
SOURCE.—O'strea virginia'na and O. edulis, which excrete a calcareous bivalved covering or shell, and inhabit the shallow coast water of the Atlantic and Indian Oceans.
DESCRIPTION.—External surface rough, inner surface smooth and white, the two toothless, hinged valves made up of imbricate, foliaceous layers, presenting, when closed, an irregularly rounded, oblong, or ovate form.
CONSTITUENTS.—Largely calcium carbonate, there being only 4 per cent. or less of animal matter present and a small percentage of silica, alumina, magnesia, and calcium phosphate and sulphate.
USES.—Antacid. The shell, to be used, should first be thoroughly purified and washed in boiling water. Dose: 5 to 15 gr. (0.3 to 1 Gm.).