Tissue left in a fixative beyond the defined amount of time may become excessively hard.

• A. True
• B. False
• C. Both
• D. Neither

Answer: (A)

Fixation stabilizes tissue by forming cross-links between proteins. When tissue stays in fixative longer than the recommended time, cross-linking continues and the tissue becomes increasingly rigid. This excessive hardening leads to brittleness, makes sectioning harder, and can impede stain penetration and downstream analyses. So, tissue left in fixative beyond the defined time may indeed become excessively hard. Under-fixation causes poor preservation and softness, not hardening, which is why over-fixation matches the observed effect.