H & E stained sections show very uneven staining of the tissue, with poor nuclear detail. One possible cause is:

• A. Water in the clearing agent
• B. Over-staining
• C. Under-fixation
• D. Excess embedding medium

Answer: (A)

Uneven staining with poor nuclear detail often points to problems in the clearing step. Clearing agents (like xylene) replace alcohol and render the tissue transparent so paraffin can infiltrate uniformly. If water remains in the clearing agent or clearing isn’t performed properly, the tissue won’t clear evenly, leading to inconsistent paraffin infiltration and variable stain uptake. That means nuclei may appear patchy or faint because hematoxylin’s ability to reveal nuclear detail depends on a consistent, well-cleared, and dehydrated tissue.

The other possibilities don’t fit as well: over-staining produces uniformly too-dark sections; under-fixation typically yields overall poor morphology and fragile tissue rather than patchy nuclear detail; excess embedding medium can cause mounting or sectioning artifacts but isn’t a typical cause of uneven nuclear staining.