Histotechnology I- Miscellaneous
Question No. 2. The Answer is: (B) 1 and 3 are true.
1. Gomori's methanamine silver (GMS).
3. Periodic acid Schiff (PAS).
Discussion: PAS and GMS stain are often
used to detect fungal organisms such as Histoplasma, Candida,
Blastomyces and other fungal organisms. GMS stain shares a similarity with
PAS stain in asking for an oxidizing step at the beginning of the procedure. In
PAS stain, periodic acid is used and in GMS stain, chromic acid is used. At this
initial step, the hydroxyl groups (-OH) will be oxidized to aldehyde groups (-CHO).
In GMS stain, the tissue is then treated with methenamine silver solution. Silver ions will be reduced to silver metal by the
aldehyde groupsand give a black color. In PAS stain, the aldehyde group will
react with the Schiff reagent to form an amide that gives the purple red color. In contrast to PAS stain, chromic acid,
however, is a strong oxidizing agent and will oxidize some of the aldehyde group
further to substance that would not be able to react with silver ion. With this
token, the background produced by collagen and basement will be suppressed.
Light green is used as a counterstain in GMS stain.
Von Kossa's silver deposition method is used to detect calcium. It involves the exposure of slides in silver ion containing solution to strong light but no oxidizing agents are involved. Van Gieson stain is used to study connective tissue and does not involve any oxidizing steps.