The Periodic Acid-Schiff (PAS) stain is a histochemical technique used to detect polysaccharides such as glycogen, mucosubstances, and glycoproteins. The periodic acid oxidizes the glycol groups in these molecules to form aldehydes, which then react with the Schiff reagent to produce a distinctive magenta color. This technique is especially useful for identifying glycogen storage diseases and certain types of tumors.
