Which statement is true about Harris hematoxylin?

• A. Its hematein was traditionally formed by mercuric oxide
• B. Its pH is adjusted with citric acid
• C. It is the most preferred for IHC stains
• D. It dissolves in water

Answer: (A)

Harris hematoxylin relies on oxidizing hematoxylin to hematein using mercuric oxide. That in situ formation of hematein, followed by complexing with a mordant, gives the characteristic blue-black nuclear stain. This reliance on mercuric oxide to produce hematein is what makes the statement true. The pH adjustment in Harris formulations isn’t specifically defined as using citric acid, and in practice other acids or bases can be used; the stain is not chosen for IHC as the preferred hematoxylin due to its heavy-metal content and staining behavior, and the solution is not water-soluble but is typically alcohol-based.