Formalin penetrates rapidly but fixes slowly.

• A. True
• B. False
• C. It penetrates slowly and fixes rapidly
• D. It does not penetrate tissue at all

Answer: (A)

Formalin’s behavior involves two separate steps: diffusion into tissue and the chemical fixation that follows. It diffuses into tissue rapidly, so the outer layers become saturated quickly. However, the actual crosslinking of proteins—the fixation process—occurs more slowly, especially toward the center of thicker specimens. Because diffusion can outpace fixation, you end up with rapid penetration but slower fixing. This is why the statement is true: formalin moves in quickly, but the preservation reactions take longer to complete. In practice, tissues are cut to thinner sections and fixed for appropriate times to ensure complete fixation throughout.