PAS reaction performed on semithin epon sections following removal of the resin by NaOH in absolute ethanol.

Different results of PAS reaction performed on semithin sections of Epon-embedded tissues were obtained when the sections were exposed for various time intervals to saturated solution of NaOH in absolute ethanol, the reagent known to dissolve the resin and facilitate staining. In the untreated sections only glycogen revealed strong PAS reaction, most mucosubstances reacted weakly or not at all. After 1 to 5 min of NaOH in absolute ethanol treatment results observed were in accordance with those usually seen in paraffin sections. When, however, the time of Epon-dissolving procedure was longer than 10 min, most tissue structures demonstrated positive, largely diffuse staining. The mechanism of the observed effect and its significance for the application of PAS reaction to Epon sections are discussed.