Which factor is most likely to cause hard and shrunken tissue during microtomy?

• A. Temperature of the infiltrating paraffin
• B. Blade sharpness
• C. Section thickness
• D. Fixative duration

Answer: (A)

The main factor here is how the tissue is embedded in the paraffin. The temperature of the infiltrating paraffin controls how well it penetrates and surrounds the tissue during embedding. If the paraffin is too cold, it solidifies quickly around the tissue and infiltrates poorly, which can trap air and cause the tissue to contract as it cools. That rapid solidification also makes the block more brittle and prone to appearing hard and shrunken when you attempt to section it. Using paraffin at an appropriate temperature allows smoother, uniform infiltration and minimizes shrinkage and hard spots, producing sections that cut cleanly.

Blade sharpness, section thickness, and fixative duration each influence other aspects of section quality. A dull blade tends to tear or gouge tissue, section thickness affects how the section sits on the slide, and fixative duration mainly affects fixation-induced hardening, not the embedding-related shrinkage you see during microtomy.