Description: Fontana-Masson stains argentaffin granules and melanin. Melanin is a nonlipid, nonhematogenous pigment. It is a brown-black pigment present normally in the hair, skin, retina, iris, and certain parts of CNS. Argentaffin granules are found in carcinoid tumors. The argentaffin cell granules or melanin will be stained black. The nuclei will be stained pink-red. The cytoplasm will be stained pale pink.

Solutions and Reagents:

10% Silver Nitrate Solution:

      Silver nitrate ---------------------------- 10 g

      Distilled water ------------------------- 100 ml

Fontana Silver Nitrate Stock Solution:

      Silver nitrate, 10% ------------------- 25 ml

      Ammonium hydroxide, concentrated, added drop by drop (approximately 1.0 ml) until the       precipitate that forms is just clear. If ammonium hydroxide was added too much, add 10% silver nitrate drop by drop until the solution becomes slightly cloudy. Leave solution overnight. Store solution in dark at room temperature. Stock solution is stable for approximately 6 months.

Fontana Silver Nitrate Working Solution:

      Fontana silver nitrate stock solution --- 25 ml

      Distilled water ----------------------------- 75 ml

      Filter is not necessary. Discard after use.

Gold Chloride Working Solution:

      Gold chloride solution, 1% stock -------- 10 ml

      Distilled water ---------------------------- 40 ml

Procedure:

1.   Deparaffinize and hydrate slides to distilled water.

2.   Place slides in Fontana silver nitrate working solution and leave in a 56 C oven for 2 hours. Slides may be checked after 1 hour.

3.   Rinse in 3 changes of distilled water.

4.   Tone in gold chloride working solution for 1 minutes.

5.   Rinse in distilled water.

6.   Place in 5% sodium thiosulfate solution for 1 minutes.

7.   Rinse in distilled water.

8.   Counterstain with nuclear fast red solution for 2-5 minutes

9.   Rinse thoroughly in distilled water twice.

10. Dehydrate, clear and coverslip, using a synthetic mounting medium

Results:  

      Argentaffin cell granules or melanin --------- black

      Nuclei -------------------------------------------- pink-red

      Cytoplasm --------------------------------------- pale pink  

Positive Controls:  

      Hair, skin for melanin, and small intestine for argentaffin.