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Histochemistry of calcium oxalate has not been definitive. The present author has critically investigated various histochemical methods for calcium salts and finally found a new method advantageous to those hitherto reported.Celloidin models of calcium salts, rat kidneys of oxalosis induced with ethylene glycol and human materials were used for study.New method: Firstly calcium phosphate and carbonate are removed by immersing sections into 5% acetic acid for 30 minutes. Secondly the sections still containing calcium oxalate are made to react with 5% aqueous silver nitrate for 15 minutes, and thirdly the reaction product appears dark brown to black with the use of rubeanic acid (saturated rubeanic acid in 70% alcohol with 2 drops of strong ammonium for 1 minute) that is very sensitive to silver without loosing the definite localization of calcium oxalate. This method has a merit; it does not depend on weather or illumination and takes a shorter time than the Kóssa method.A confident histochemical method for identifying calcium oxalate was established by combining this method with other characteristics of calcium oxalate such as the unstainability with hematoxylin, birefringency, solubility after incineration and gypsum formation.In the present study calcium oxalate was also found to react with lead besides silver and to appear brownish-black when one uses lead nitrate and ammonium polysulphide.
Takao Yasue (Wed,) studied this question.