In Bouin-fixed tissue, insufficient removal of picric acid before processing tends to cause which staining problem?

• A. Poor nuclear staining
• B. Overstaining of nuclei
• C. No change in staining
• D. Hyperchromasia of cytoplasm

Answer: (A)

The main idea here is how Bouin fixative interacts with subsequent staining. Bouin’s solution contains picric acid, which is highly acidic. If picric acid isn’t thoroughly removed before dehydration and embedding, the tissue stays in a more acidic environment. This acidity interferes with hematoxylin’s ability to bind and stain nuclear material effectively, so the nuclei appear weak or poorly defined. The eosin in the counterstain can still stain the cytoplasm, but the nuclear detail is lost or diminished, which is why poor nuclear staining is the outcome you’d expect. Thorough washing to remove picric acid before processing helps restore proper nuclear staining.