The volume of fixative should exceed the volume of the tissue by how many times?

• A. 1-2 times
• B. 5-10 times
• C. 15-20 times
• D. 30-40 times

Answer: (C)

Fixation works best when the tissue is surrounded by an excess of fixative so it can diffuse in and react without the liquid becoming depleted. As fixation proceeds, the fixative is consumed and binding products form, which can change concentration, osmolarity, and pH if the surrounding volume isn’t ample enough. By using about 15–20 volumes of fixative for every tissue volume, you keep the fixative in excess throughout the process, allowing thorough penetration and uniform cross-linking of proteins. Smaller ratios (1–2 or 5–10) risk incomplete fixation, especially in thicker specimens, while much larger ratios (30–40) waste fixative without providing meaningful additional benefit. Hence, 15–20 times is the recommended range.