Which reagent is used as the impregnating solution in Bodian's method?

• A. Protargol Solution
• B. Ferric Ammonium Sulfate Solution
• C. Aqueous Silver Nitrate
• D. Sodium Thiocyanate

Answer: (A)

In Bodian's method, the key step is silver impregnation of neural tissue using a preformed silver-protein complex. Protargol is this impregnating solution: a colloidal silver proteinate that penetrates tissue and deposits silver along nerve fibers. This creates a strong, selective contrast that makes axons and other neural elements visible after the subsequent development/toning steps (often with gold chloride) to intensify the appearance. Protargol’s stable, controlled release of silver gives reliable impregnation with relatively low background compared with other silver methods.

The other reagents listed serve different roles in various silver-staining approaches or in later stages of Bodian staining, but they are not the impregnating solution used in this method. Ferric ammonium sulfate can act as a mordant/differentiator in some protocols; aqueous silver nitrate is used in other impregnation schemes; sodium thiocyanate is typically involved in differentiation or background reduction steps.