What is used in the clearing portion of the processor?

• A. Xylene
• B. Ethanol
• C. Water
• D. Toluene

Answer: (A)

Clearing in tissue processing is the step that replaces the alcohol used during dehydration with a solvent that can mix with and allow infiltration of paraffin. Xylene fits this role well because it is a nonpolar solvent that readily dissolves any remaining alcohol and is miscible with paraffin, enabling complete clearing and ready paraffin infiltration for embedding. Ethanol and water are too polar to effectively replace alcohol and to blend with paraffin, so they don’t serve as clearing agents. Toluene can be used as an alternative clearing agent in some protocols, but xylene is the traditional and most commonly taught choice for this step, which is why it’s the best answer here.