FACTORS AFFECTING THE FORMATION OF METALLIC SILVER AND THE BINDING OF SILVER IONS BY TISSUE-COMPONENTS

The rate of formation of metallic Ag has a maximum when plotted as a function of pH. The site of this maximum on a pH scale differs noticeably for various tissue [human spinal cord] elements. The amount of Ag ions bound to the tissue is a monotonously increasing function of pH. A temperature rise decreases the length of the induction period and increases the gradient of the ascending section of the kinetic curve representing the formation of metallic Ag. It increases the maximum amount of Ag ions bound to the tissue. An increase in concentration (activity) of the Ag ions in the impregnating bath has the same effect. Chemical composition and concentration of the complexing agent, as well as special ions in the impregnating bath to which earlier some definitive role was attributed in the Ag staining methods, proved ineffective when pH and activity of Ag ions were kept constant. Illumination of the reaction was also ineffective. The kinetic curves obtained in nonaqueous but polar media (e.g., acetone) exhibited the same qualitative characteristics as those obtained in aqueous solutions. No reaction between Ag ions and tissue was observed in apolar solvents.