The preferred fixative for best carmine is?

• A. Absolute alcohol
• B. Formalin
• C. Bouin
• D. Glacial acetic acid

Answer: (A)

The staining method relies on an alcoholic environment to preserve and reveal carbohydrate-containing structures that Best’s carmine targets. Fixation with absolute alcohol dehydrates and hardens tissue without introducing water or strong cross-links, so the tissue components remain well-preserved and accessible to the alcohol-based carmine solution. This compatibility gives better penetration and more uniform, intense staining of mucopolysaccharides and glycogen.

Formalin is water-based and forms cross-links that can mask carbohydrate residues, reducing stain uptake. Bouin’s fixative contains picric acid and is more aggressive and can alter color stability, which can interfere with the carmine reaction. Glacial acetic acid is harsh and can distort morphology and extraction of certain tissue components, also compromising stain quality.