The silver ion can be used to demonstrate a wide variety of structures and substances. These range from spirochetes and intracellular organelles as the Golgi substance to glycogen, ascorbic acid, and urates. All the various methods employ one of two basic principles in producing the histologic result, namely the argentaffin reaction and the argyrophilic reaction. These two principles have been well defined by Gomori.1 In the argentaffin reaction the silver ion is fixed in place by the ability of the specific structure or substance to reduce it. In argyrophilia an extrinsic reducing agent such as hydroquinone must be used, and impregnation and reduction of the silver ion in the appropriate location depend on the specific conditions under which the procedure is performed.
It has been only within recent years that steps have been taken to control the ion strength, pH, temperature, and oxidation-reduction