Mineralized spherules in the cells and matrix of calcifying cartilage from developing bone

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Abstract
Fresh tibias and occipital bones from newborn mice and rats, as well as from 18‐day‐old mouse and chick embryos, were stained with 10% GBHA and 5% AgNO3solutions to localize calcium and phosphate or carbonates in sphenules within the cytoplasm of chondrocytes and in the matrix of the calcifying cartilages. The mineralized spherules in the matrix adjacent to the hypertrophied chondrocytes were approximately 0.5 to 1 μ in diameter. This was comparable in size to the spherules found within the cytoplasm of the chondrocytes. The spherules within the core of the spicules distal to the hypertrophied chondrocytes were about 2–3 μ in diameter. The larger spherules were shown to contain an organic core which stained metachromatically with toluidine blue and was also stained with aldehyde fuchsin. The spherules were not visible after PAS reactions due to the intense staining. The labile GBHA and silver acetate positive spherules localized in the chondrocytes may be the source of the extracellular mineralized spherules.