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IN a previous communication by one of the present authors [Robison, 1923] it was shown that the bones and ossifying cartilage of young animals contain an enzyme which rapidly hydrolyses hexosemonophosphoricl ester and glycerophosphoric ester with liberation of free phosphate ions. The kidney was found to possess a similar hydrolytic power, but liver, spleen and pancreas were much less active in this respect, while muscle and the non-ossifying cartilage were almost or entirely without action on these monophosphoric esters.A hexosediphosphatase, which hydrolyses at least one of the phosphoric acid groups of hexosediphosphoric ester, appeared to be more commonly distributed, being found in each of the tissues named above.The suggestioii was put forward that the former of these enzymes, the "monophosphoric esterase" present in bone, is concerned in the process of ossification by effecting the hydrolysis of phosphoric esters contained in the blood, thus bringing about a local increase in the concentration of inorganic phosphate ions, so that the product of the concentrations of phosphate and calcium ions becomes greater than the solubility product of calcium phosphate, which is thereupon deposited in the solid state.The present paper is an account of further work on this enzyme.Method of Extraction. The tissues were thoroughly ground in a mortar with ten or twenty times their weight of water (or a 0*4 % solution of sodium bicarbonate) saturated with chloroform. In some of the later experiments these extracts (termed "10 %" and " 5 % " respectively) were allowed to remain at 0°d uring 24 hours and were then filtered.

The medical literature of the present time is replete with discussions of the biochemical r\l=o^\leof the element calcium. The

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