This procedure is used in the PAS reaction to block hydroxyl and amino groups. It does this by forming esters with them. As a consequence some carbohydrates fail to react with the Schiff's reagent. This may be used as a means of identifying them, particularly if done in conjunction with other blocking procedures.


Chemical Amount
Acetic anhydride 16 mL
Pyridine, anhydrous 24 mL


Place dewaxed sections into the solution at the temperature specified for the time given.

Tissue Temp Time State
Cartilage 58°C 6 hours complete
Cartilage 25°C 24 hours complete
Glycogen 25°C 6 hours Almost complete
Epithelial mucin 25°C 6 hours complete



Lillie, R.D., (1954)
Histopathologic technique and practical histochemistry Ed.2
Blakiston, New York, USA.




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