Which solvent is used in the clearing portion of the processor as stated in the material?

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

Answer: (A)

Clearing is the step where the tissue, after dehydration, is transferred into a solvent that is compatible with paraffin so that infiltration can occur and the tissue becomes optically transparent. The solvent chosen must mix with both the dehydrating alcohol and the paraffin to remove the alcohol and substitute it with paraffin. Xylene fits this role best because it is miscible with ethanol (the dehydration solvent) and with paraffin, allowing complete removal of the alcohol and efficient paraffin infiltration, which makes the tissue ready for embedding. Water cannot clear because it would not replace alcohol or permit paraffin infiltration; ethanol has already served as a dehydrant and would not effectively replace itself in the clearing step; isopropanol is not the standard clearing agent in most processors.