What is the purpose of adding acetic acid to Harris hematoxylin?

• A. Make nuclear staining more specific
• B. Increase background staining
• C. Stain cytoplasm more darkly
• D. Fix tissue

Answer: (A)

Acetic acid is added to Harris hematoxylin to adjust the staining environment so nuclei stain more selectively and crisply. The acidic medium enhances the affinity of hematoxylin for nucleic acids, giving nuclei a deeper, more uniform blue color while minimizing non-nuclear background staining. This makes nuclear detail stand out without over-staining the cytoplasm. It isn’t used to fix tissue (fixation is done with other reagents), nor does hematoxylin staining target cytoplasm (that’s the role of eosin in routine stains).