Orthochromatic and metachromatic staining reactions by pyronin Y on Epon semithin sections

Semithin sections from glutaraldehyde-fixed, Epon-embedded tissues were stained by aqueous solutions of pyronin Y at increasing concentrations (from 10(-6) to 10(-3) mol). Mucopolysaccharide containing structures (e.g. mucin) were found stained in orange, meanwhile the chromatin and remaining tissue components appeared in a bright pink-red color. Cytophotometric measurements showed that a metachromatic shift occurs in the mucin content from goblet cells after pyronin Y staining at 10(-3) mol. Some features of the metachromatic reactions by cationic dyes are briefly discussed.