Mucopolysaccharides metachromasia

Metachromasia, from meta, a change in the kind of, and chroma, color, refers to the qualitative change which occurs in the color of certain dyes when they interact with other substances. The term was originally applied by Paul Ehrlich to the phenomenon of color change when a dye is adsorbed onto a substrate. Thus, cartilege and other mucopolysaccharide-containing tissues are stained red by toluidine blue. Similarly, Hartley observed that when bromophenol blue solution is added to cetrimide solution the color changes from purplish blue to clear blue. 

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