Heat should only be applied during which processing step to avoid hard and brittle tissues?

• A. Dehydration
• B. Infiltration
• C. Clearing
• D. Embedding

Answer: (B)

Heat is used intentionally during the infiltration stage to melt paraffin and drive it into every part of the tissue, replacing the residual solvent and moisture. This creates a solid, wax-embedded block that remains pliable enough for clean, thin sectioning. If heat were applied during dehydration or clearing, the tissue could over-dry, shrink, or be distorted by the solvents, making it hard and brittle. Embedding uses heat too, but by the time infiltration has thoroughly permeated the tissue, the block is already stabilized; the critical moment for controlled heating to preserve tissue integrity is during infiltration.