Which dye is used in processing alcohols to dye tissues for identification when embedding?

• A. Methylene blue
• B. Hematoxylin
• C. Crystal violet
• D. Eosin

Answer: (A)

Tracking dye used during processing is added to the alcohols so you can visually follow tissue as it moves through dehydration and clearing. Methylene blue provides a bright blue color to the tissue, making it easy to see tissue boundaries, confirm adequate infiltration, and ensure proper orientation before embedding in paraffin. This helps catch issues like tissue loss or incomplete dehydration early. The other dyes listed are intended for post-embedding staining (for diagnostic purposes), such as hematoxylin and eosin for H&E slides or crystal violet for Gram stains, and would not be suitable for monitoring processing because they stain differently and could interfere with infiltration and later steps. Methylene blue is chosen specifically because it is easy to wash out and does not affect subsequent embedding or staining.