Some chemical principles applicable to some silver and gold staining methods for neuropathological studies.

Some of the chemical principles involved in some silver and gold staining procedures for neuropathological studies are analyzed in the light of experience with methods for astrocytes, microglia, axons and reticulin fibers. The role of formalin fixation, and of treatment with ammonium bromide or oxidizing agents prior to staining for glial cells or reticulin fibers respectively, is described. The silver staining methods are divided into two fundamentally different groups. One is based on the use of silver diammine solutions with or without other substances such as carbonates or pyridine, and at varying times, gold toning. This group encompasses a great variety of techniques for staining glial cells, reticulin fibers and axons. The second group is based on the use of weak solutions of silver ions, reduction in a photographic developer, treatment with gold chloride, and a second reduction in oxalic acid. This group is represented by methods for staining axons and reticulin fibers. A brief analysis of the gold and mercuric chloride methods for astrocytes is also given.