Fontana-Masson requires a fixative that should be avoided because it dissolves argentaffin granules. Which fixative is to be avoided?

• A. Alcohol
• B. 10% Neutral Buffered Formalin
• C. Formalin
• D. Acetone

Answer: (A)

Fontana-Masson staining targets argentaffin granules, which must be preserved during fixation for reliable silver impregnation. Alcohol is a dehydrating solvent that can dissolve or extract argentaffin granules from tissue, so using it as a fixative compromises the very constituents the stain is designed to reveal. That’s why alcohol should be avoided. In contrast, formalin or neutral buffered formalin cross-links and preserves cellular components, keeping argentaffin granules intact so the silver deposition works properly. Acetone, another strong organic solvent, can also disrupt delicate granules, but the guidance most often emphasized for Fontana-Masson is to avoid alcohol.