Silver staining of protoplasmic astrocytes by physical development.

The protoplasmic astrocytes adsorb complex Ag(SCN)2- ions from a 40% sodium rhodanide solution containing 1% silver nitrate. The complex is decomposed during a subsequent washing with 5% sodium carbonate, by the excess of rhodanide ions being removed from the sections. Thus, colloid AgSCN grains are made to deposit in the protoplasmic astrocytes. These grains will be reduced first to metallic silver, then enlarged to microscopic dimensions by means of a special physical developer, rendering the protoplasmic astrocytes visible. A pretreatment with 0.01% iodine dissolved in 5% potassium iodide is used to suppress the simultaneous staining of some unwanted tissue elements.