In which hematoxylin was the hematein traditionally formed by mercuric oxide?

• A. Harris
• B. Mayer
• C. Ehrlich's hematoxylin
• D. Weigert's hematoxylin

Answer: (A)

Hematein is the active form of hematoxylin that must be produced by oxidation before it can bind with the mordant to stain nuclei. In the Harris formulation, hematoxylin is oxidized to hematein using mercuric oxide, which creates the stable, nuclear-staining complex that gives the crisp blue-black nuclei seen with this stain. Other hematoxin formulations use different oxidants or systems to generate the active dye, so the specific mercuric oxide oxidation is a hallmark of Harris hematoxylin. That’s why this option is the best choice.