If water bubbles are observed on an H&E slide, what step should be verified for completeness?

• A. Dehydration
• B. Clearing
• C. Staining time
• D. Fixation

Answer: (A)

Water bubbles on an H&E slide mean moisture is still present in the tissue. Dehydration is the step that removes water from the tissue by passing the section through graded alcohols until it is in absolute alcohol. If this step isn’t completed properly—insufficient time in 100% alcohol, degraded or old alcohol, or incomplete exchanges—the tissue retains water. That residual water can trap air or form droplets when the slide is later cleared and mounted, showing up as bubbles under the coverslip. So the key is to verify that dehydration was fully and adequately carried out before moving on to clearing and mounting, ensuring sufficient time and proper alcohol concentrations to remove all water.