In a silver stain for reticulin, what role does phosphomolybdic acid serve?

• A. Oxidizer
• B. Reducing agent
• C. Stabilizer
• D. Solvent

Answer: (A)

Phosphomolybdic acid acts as an oxidizing step that primes the tissue for silver deposition. It oxidizes tissue components and forms a complex that makes reticular fibers receptive to silver during the development step, so the fibers become argentophilic and stain darkly. The actual reduction of silver to metallic silver is carried out by the developer later, not by phosphomolybdic acid. It’s not a reducing agent, stabilizer, or solvent, which is why those options don’t fit. Omitting this oxidation step often yields weak or nonspecific reticular staining.