Ccxvii. the Possible Significance of Hexosephosphoric Esters in Ossification

IN the preceding paper [Robison and Soames, 1930] it was shown that, although bone slices from rachitic animals will calcify in solutions of inorganic salts supersaturated with respect to the bone phosphate, at lower concentrations of calcium and inorganic phosphate calcification will only occur in presence of phosphoric ester. At critical concentrations of the inorganic radical as little as 0*5 mg. per 100 cc. of phosphorus in the form of ester is sufficient to determine calcification, this amount being similar to that found in plasma. The solutions used for these experiments contained no protein and no other organic constituent but phosphoric ester. The concentration of calcium ions was, therefore, higher than in plasma even when the total calcium content was the same. The solutions further differed from plasma in containing much less bicarbonate. The experiments described in the present paper deal with the effect of bicarbonate, sodium, potassium and magnesium on calcification in protein-free solutions at different levels of calcium and inorganic phosphate, in absence and in presence of phosphoric ester. Experiments on the effect of antiseptics, of previous treatment of the bone slices with organic solvents or of desiccation in vacuo have also been carried out. The results of these have set in sharp distinction two mechanisms in calcifying hypertrophic cartilage, the phosphatase mechanism which can produce in the matrix a local supersaturation sufficiently great to cause deposition of the bone phosphate, and the second, still obscure, mechanism, which favours, and may determine, deposition of the bone phosphate from its supersaturated solution.