Bone composition was investigated by analysis to determine distribution of basic and acid equivalent substances, bone-ash solubility tests, and attempts to bring about the formation of basic phosphates in vitro under conditions compatible with life. The percentage of Ca, PO4, Na, K, CO3, and Mg was very slightly affected by treatment of bone with boiling glycerin and KOH according to Gabriel''s (''94) method. After extraction of fats with CCl4 the author obtained the ratio: Ca:PO4:CO3: :1:0.57:0.11 as against Gabriel''s ratio: Ca:PO4:CO3: : 1:0.58:0.14. Analysis of bone ash shows presence of basic Ca phosphate. By reaction between phosphate mixtures of different pH values and at varying temperatures, especially 37[degree] C, and CaCl2 solution, Ca phosphate precipitates are formed instantly, and especially at pH 7.35. Extreme difference between rapidity of Ca phosphate formation in vitro and slowness of bone formation is accountable by the formation in bone of stronger basic phosphates and by the powerful buffering ability of tissue fluids. Bone is composed chiefly of basic Ca phosphate of the composition 3 Ca3(PO4)2 [image] Ca(OH)2, alkali-carbonates and -bicarbonates being admixed.