In regressive hematoxylin staining, what is the purpose of differentiating in acid-alcohol?

• A. To remove excess stain
• B. To promote background staining
• C. To fix tissue
• D. To dehydrate

Answer: (A)

Differentiating in acid-alcohol during regressive hematoxylin staining is used to remove excess stain and sharpen nuclear detail. The tissue is first over-stained with hematoxylin, then acid-alcohol washes away the stain from areas where it isn’t tightly bound, leaving the nuclei—where the stain binds more strongly—clearly defined and reducing background. This selective decolorization creates crisper contrast and accurate nuclear visualization.

The other steps described—fixing tissue, and dehydration—are not accomplished by this differentiation step; differentiation specifically targets excess stain to fine-tune intensity rather than fix or dehydrate.