When cutting paraffin-embedded tissue, if the tissue seems hard and brittle, a likely source of trouble is:

• A. Overheated paraffin
• B. Overhydrated tissue
• C. Under-fixed tissue
• D. Over-cleared tissue

Answer: (A)

The key idea is that the embedding medium’s temperature can directly affect how the tissue behaves during microtomy. If paraffin is overheated, it loses plasticity and the block becomes overly stiff. The heat can also damage tissue proteins, making the infiltrated tissue less able to bend with the blade. The result is hard, brittle sections that tend to crack or crumble when cut. To avoid this, keep paraffin at a controlled, appropriate temperature (usually around 60°C) and ensure the blocks aren’t exposed to wax that’s too hot before sectioning.

Overhydrated tissue tends to be too soft and may smear or tear rather than stay hard and brittle. Under-fixed tissue often lacks structural integrity and can crumble or tear rather than feel rigid. Over-cleared tissue can cause other artifacts related to excessive solvent exposure, but it doesn’t typically produce the crisp brittleness associated with overheated embedding wax.