For the detection of fungal elements in tissue sections. This is an essential stain and should be used whenever a fungal etiology is suspected.
Mechanism: Chromic acid treated fungi possess aldehydes which will reduce the hexamine-silver mixture to produce a black deposit, i.e. an argentaffin reaction. Fungi stain black.
Solutions.
1. 5% aqueous chromic acid
2. 1% aqueous sodium bisulphite
3. 5% aqueous borax
4. 0.1% aqueous gold chloride
5. 2% aqueous sodium thiosulphate
6. Stock Methenamine Silver solution.
Add 5 ml of 5% silver nitrate to 100 ml of 3% hexamine. A white precipitate will form which, on shaking, will dissolve. This solution will keep from 1-2 months at 4oC.
7. Working silver solution (filter before use).
Stock methenamine silver solution 25 ml
Distilled water 25 ml
5% Borax 1-2 ml
Method:
1. Take sections to water.
2. Oxidize in 5% chromic acid for 1 hour.
3. Wash in running tap water for 10 minutes.
4. Treat with sodium bisulphite for 1 minute to remove any residual chromic acid.
5. Wash in tap water then distilled water.
6. Place section in the working silver solution at 60oC in a water bath.