Fontana-Masson stain is used to demonstrate which substances?

• A. Melanin and argentaffin granules
• B. Hemosiderin
• C. Bile pigments
• D. Urates

Answer: (A)

Fontana-Masson relies on the silver-impregnation (argentaffin) reaction, which detects substances that can reduce silver ions. Melanin is a natural reducing substance in tissue, so it reduces silver to metallic silver and appears black. Argentaffin granules, found in certain neuroendocrine cells, also contain reducing agents and stain dark with this method. Therefore, this stain is specifically used to demonstrate both melanin and argentaffin granules. Hemosiderin, bile pigments, and urates require different stains, so they are not detected by Fontana-Masson.