The preferred fixative for the Masson Trichrome stain is

• A. Bouins
• B. Formalin
• C. Alcohol
• D. Glutaraldehyde

Answer: (A)

Masson Trichrome relies on differential dye uptake to distinguish collagen from muscle and cytoplasm, and the fixative helps set tissue in a way that maximizes this contrast. Bouin's fixative, with its picric acid content, lightly fixes and preconditions the tissue so that the subsequent staining steps produce crisp color separation. This results in collagen staining strongly with the blue (or green, depending on the variant) dye, while muscle and cytoplasm take the red stain, and nuclei remain distinctly dark after the hematoxylin step. Other fixatives—formalin, alcohol, or glutaraldehyde—can reduce this contrast, shrink or distort tissue, or hinder dye uptake in routine light microscopy. Therefore Bouin's fixative is preferred for Masson Trichrome.