CONTENTS

The quantitative aspects of silver staining of sections have been investigated with radioactive silver (Agnl). The concentrations of reducible silver, developed silver, and silver nuclei in the sections were determined, but it is doubtful if the values obtained for silver nuclei are significant. All three forms of silver increased with pH, time, and the concentration of silver in the impregnating solution. Temperature of impregnation had little effect on the uptake of reducible silver, but increased the developed silver, presumably by increasing the silver nuclei. An increase in the temperature of a hydroquinone-sulphite developer increased the amount of reducible silver reduced by the developer. The deposition of silver by a glycine physical developer was shown to follow a curve which was reasonably consistent with the assumption of a typical autocatalytic reaction. The uptake of silver by non-nervous tissues provided evidence that the process is not specific for nerves; the final specificity of staining is determined during develop-ment. The quantitative results are consistent with the hypothesis that the histidine in th