Which processing step directly precedes paraffin infiltration?

• A. Clearing
• B. Dehydration
• C. Staining
• D. Embedding

Answer: (A)

Clearing is the step that directly precedes paraffin infiltration. After dehydration, the tissue is saturated with an alcohol-based solvent that must be replaced with a clearing agent (like xylene) that is miscible with paraffin. This clearing step makes the tissue receptive to molten paraffin by removing the alcohol and preparing a medium in which paraffin can infiltrate. Once infiltration with paraffin has occurred, embedding follows to form a solid block for sectioning. Staining comes later, after sections are cut and mounted.