In routine processing, which step follows fixation?

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

Answer: (A)

After fixation, the next step is dehydration. This is needed because fixation preserves tissue by stabilizing structures, but water remains inside the tissue. Paraffin, the embedding medium, is hydrophobic and cannot penetrate or surround tissue that still contains water. By passing the tissue through a graded series of alcohols, water is gradually removed and replaced with alcohol. Once water is gone, a clearing step (usually with xylene or a similar solvent) makes the tissue transparent and ready to mix with paraffin. Finally, molten paraffin infiltrates the tissue and is used to embed it for sectioning.