When essential oils are used as clearing agents, what step must precede paraffin infiltration?

• A. Do not remove the oil; proceed to infiltration
• B. Remove the oil with a hydrocarbon such as xylene prior to paraffin infiltration
• C. Use water to remove oils
• D. Apply heat to remove oils

Answer: (B)

When essential oils are used as clearing agents, they must be removed before paraffin infiltration. Paraffin needs a solvent that is miscible with both the clearing agent and the wax. Essential oils are oily residues that paraffin cannot displace on its own, so you replace the oil with a hydrocarbon solvent like xylene, which is compatible with paraffin and can effectively exchange the clearing agent. This ensures complete infiltration and proper embedding.

Using water won’t dissolve or remove the oil, and heating to remove oils can damage tissue and still won’t effectively clear the residue. Skipping this exchange step would leave oil residues that hinder infiltration and sectioning.