Introduction

Toluidine Blue, solution is often used for metachromatic staining (characteristic for cationic or basic dyes) that partially depends on the pH level, dye concentration and temperature. During staining, blue or purple dyes display a shift into red, while red dyes display shift into yellow on metachromatic tissue elements. Metachromatic staining is typical for mucopolysaccharides (especially for those with numerous sulfate groups), cartilage, cylindrical cells and mast cell granules.