For periodic acid, these type of sections may require longer oxidation time.

• A. Thicker sections (5-7)
• B. Thinner sections (1-3)
• C. Sections must be dry before staining
• D. Overnight oxidation is required

Answer: (B)

Periodic acid oxidation works by oxidizing carbohydrates to aldehydes, and how well this happens depends on how far the oxidant can diffuse into the tissue. Tissue thickness matters because diffusion is slower in thicker sections, so inner portions may not oxidize completely unless you allow more time. That’s why thicker sections typically require a longer oxidation time to achieve even oxidation throughout the block. In contrast, very thin sections oxidize more quickly, and extending the time can lead to over-oxidation and weaker staining. Drying the sections before staining isn’t a requirement for this step, and overnight oxidation would generally overdo it. So the practical takeaway is that as section thickness increases, oxidation time should be increased; thinner sections usually need shorter oxidation times.