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THE rather meager literature on the lipides in teeth has been reviewed previously by Leopold, Hess, and Carter.' These investigators also reported that human dentin contains 0.024 per cent cholesterol. The present paper deals with the determination of cholesterol in enamel and the total lipide content of both enamel and dentin. EXPERIMENTAL Sample Preparation.-The dentin used was prepared in the same manner as that previously used for the isolation of cholesterol.1 The enamel was prepared by the method employed by Losee and Hess2 for the isolation of enamel protein.Cholesterol in Enamel.-The method of isolation of cholesterol from dentin that was most satisfactory was used for the isolation and estimation of the cholesterol in enamel. The procedure involved extraction of the enamel with an aqueous solution containing 30 per cent KCl and 1 per cent K2C03. Twenty milliliters of solution was used for each gram of enamel. After several extractions the combined extracts were treated with 0.4 Gm. of potassium acetate, 0.4 Gm. of silica gel, and 0.4 ml. of glacial acetic acid per gram of original sample. The extract was then shaken for 30 minutes, filtered with suction through a fine-sintered glass filter, and the filtrate was extracted with petroleum ether. Both the petroleum ether extract and the aqueous extract were analyzed for total cholesterol. To determine if the treatment with silica gel adsorbed any cholesterol, a recovery experiment using pure cholesterol was run in which 2 solutions, each containing 1.76 mg. of cholesterol in 100 ml. of H20, were used. One solution was treated with the same amount of silica gel used in the enamel extraction procedure and the other was used as a control. Cholesterol determinations gave a value of 1.76 mg. in the control and 1.43 mg. in the silica gel-treated solution, a loss of 18 per cent. Correction for this loss incurred in the procedure was used on the determinations of the cholesterol content of the enamel. All cholesterol determinations were made by the same method previously used.

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