Periodic Acid-Schiff (PAS) is a histochemical staining technique used to detect polysaccharides, such as glycogen and mucosubstances, in biological tissues. The method involves treating tissue sections with periodic acid, which oxidizes certain carbohydrates, followed by a reaction with Schiff's reagent that produces a magenta color. This staining is particularly useful in identifying various diseases, including diabetes and fungal infections. PAS staining is commonly employed in pathology to visualize structures like basement membranes and mucins. It helps pathologists differentiate between normal and abnormal tissue, aiding in the diagnosis of conditions such as carcinomas and glycogen storage diseases. The technique is valued for its specificity and sensitivity in detecting carbohydrate-rich components.