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
Benzoyl chloride 2 mL
Pyridine, anhydrous 38 mL


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

Tissue Temp Time State
Cartilage 58°C 6 hours Almost complete
Glycogen 58°C 6 hours complete
Epithelial mucin 58°C 2 hours complete



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




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