What is the standard fixative for routine histology and why?

• A. Neutral-buffered formalin preserves tissue morphology by cross-linking proteins.
• B. Bouin's solution preserves nucleic acids best.
• C. Ethanol preserves tissues by dehydration.
• D. Glutaraldehyde is the standard fixative for routine histology.

Answer: (A)

The main idea is that fixation aims to lock cellular structures in place so tissues don’t degrade and can be reliably examined under a light microscope. Neutral-buffered formalin, used at about 10%, is the standard for routine histology because it quickly penetrates tissues and cross-links proteins through formaldehyde to form methylene bridges, stabilizing the architecture of cells and extracellular components. The buffering keeps the pH near neutral, which minimizes artifacts and distortion that acidic fixatives can cause. This combination yields reliable, well-preserved morphology that is compatible with paraffin embedding and routine stains like hematoxylin and eosin. Other fixatives have their uses—Bouin’s can give excellent morphology but brings hazards and staining complications from picric acid; ethanol fixes by dehydration but doesn’t preserve structure as well; glutaraldehyde excels for ultrastructure and electron microscopy but isn’t ideal for standard paraffin sections and routine histology.