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The effect was studied of various polyvalent metal ions on the metastability of a calcification buffer. At concentrations of 1 ~M or less, Pb *+, Fe e+, Fe 3+, Cr a+, Bi a+ and A1 a+ ions were found to destabilize the buffer. The results suggest that insoluble phosphates formed by these ions initiate the precipitation of calcium apatite. The implications of these findings to pathological calcification and calciphylaxis are discussed.

A method for the microdetermination and ultramicrodetermination of calcium in blood serum, urine, and inorganic salt solutions has been developed. Calcium was titrated with disodium ethylenediaminetetraacetate, and Cal-red as the indicator, using a Gilmont ultramicro-buret of 0.1-ml. capacity. Amounts of 5 to 30 µg. of calcium per sample, of 0.05- to 1-ml. volumes, can be determined with a reproducibility of 1 to 2 per cent. The difference between the values found for serum calcium with the Cal-red and the oxalate method had a standard deviation of ±3.32 per cent. Serum magnesium can be determined as the difference of two simple titrations. Phosphate levels up to 30 mg. per 100 ml. P did not interfere with the determination in serum, even when the calcium level was raised to about 20 mg. per 100 ml. Up to products of 80(Ca X P, expressed in mg. per 100 ml.) there was no interference, in inorganic salt solutions. At higher products drift occurred, but the addition of some citrate to the solutions enabled the attainment of sharp end points at Ca X P products up to approximately 1000. Urinary calcium was determined satisfactorily, without the occurrence of drift, if citrate was added to the solution. Magnesium did not interfere appreciably, giving only 1 per cent higher readings at levels of 20 mg. per 100 ml. The interference of copper and iron was removed by the addition of sodium cyanide.

Sheep bone collagen, rat tail tendon collagen and apatite seeds were used in a model system to study nucleation catalysis and mineral deposition in a metastable calcification buffer.Sheep bone collagen was shown to be a good nucleation catalyst, while earlier experiments have shown that rat tail tendon collagen was a very poor catalyst.The rapid phase of apatite deposition in the collagen was terminated as soon as a mineral content of not more than 50--60 per cent was reached, although the buffer was still highly supersaturated.The results suggest that the amount of mineral deposited in such a model system is regulated by factors similar to those operating in biological calcification.Key words: Nucleation --Mineralization --Bone --Collagen --Apatite.Nous avons utilis6 de la collag6ne d'os de mounton et de tendons de queues de rats et des cristaux d'apatite pour 6tudier dans un syst6me mod61e la catalysation de la nucl6ation et la d6position de min6ral dans un tampon m6tastabile.La collag~ne d'os de mouton se trouvait ~tre un bon catalysateur, tandis que des exp6r-iences ant6rieures ont d6montr6 que la collag~ne de tendons de queues de rats 6tait un cata-]ysateur tr~s faible.Le phase rapide de la d6position de l'apatite dans la collag~ne se termine aussitSt que le contenu du minSral a attaint au plus 50 s 60 pour cent, bien que la supersaturation du tampon est encore bien ~lev6e.Les r6sultats montrentl que dans un tel syst~me module la quantit6 du depSt min6ral est r@gl6e par des facteurs semblables & ceux qui opbrent pendant la calcification biologique.Kollagen aus Schafsknochen und Rattenschwanzsehnen und Apatitkeime wurden verwendet in einem ModeI1-System zur Untersuchung der katalytischen Nukleation und der F~llung von Mineral in einem metastabilen Calciumphosphatpuffer.Kollagen aus Schafsknochen war ein guter Katalysator ffir die Nukleation, w~hrend in frfiheren Versuchen sich herausstellte, dab Rattenschwanzkollagen ein ganz schlechter Katalysator ist.Die schnelle Phase der Apatitf~llung im Kollagen war beendet, wenn der Mineralgehalt bis zu 50--60% angestiegen war, obwohl der Puffer noch stark iibers~ttigt war.Die Resultate weisen daraufhin, dab die Menge des gef~llten Minerals in einem solchen Modell-System von ~hnlichen Faktoren reguliert wird wie die biologische Verkalkung.