The periodic acid Schiff reaction (PAS) is used to demonstrate the presence of 1-2-glycols, and is consequently an important method in the histochemistry of carbohydrates and the histological demonstration of many structures.
Lillie referred to this method as The Periodic acid, Schiff Sulfite Leucofuchsin Reaction, short variant.
Tissue sample
5µ paraffin sections of neutral buffered formalin fixed tissue are suitable.
Other fixatives are likely to be satisfactory, although glutaraldehyde should be avoided.
Method
Bring sections to water via xylene and ethanol.
Oxidise in periodic acid for ten minutes.
Wash in running water for five minutes .
Place in Schiff's reagent for 10 minutes.
Transfer to three successive baths of sodium metabisulphite
for 1, 2 and 2 minutes respectiively.
Wash in running tap water for 5 minutes.
Counterstain with one of the following:–
Place in Mayer's hemalum for 2 minutes.
Wash in running tap water and blue.
Place in Weigerts iron hematoxylin for 2-4 minutes.
Decolourise with Pal's bleach diluted 1:5 with distilled water.
Wash in running tap water for 4 minutes.
Place in Weigerts iron hematoxylin for 6 minutes.
Wash for 4 minutes in running tap water.
Place in saturated aqueous picric acid for 1 minute.
Dehydrate with ethanol, clear with xylene and coverslip using a resinous medium.
Expected results
1-2-glycols – red
Nuclei – blue or black
Cytoplasm – yellow or unstained
Notes
The nuclear counterstain may obscure some positive staining. Keep the application time short.
Weigert's solution should be allowed to ripen for an hour before use.
