A component of the Masson trichrome stain is which of the following?

• A. Acid fuchsin
• B. Methyl green-pyronin
• C. Toluidine blue
• D. Basic fuchsin

Answer: (A)

Masson's trichrome uses three dyes to differentiate tissue components: a red stain for muscle and cytoplasm, a blue stain for collagen, and a nuclear counterstain. The red component in this stain is acid fuchsin, which binds to cytoplasmic proteins and muscle fibers to give them a red color. After differentiation, the collagen is colored blue by another dye (commonly aniline blue), while nuclei are darkened by the nuclear counterstain. The other dyes listed are used in different staining schemes or contexts, not as the red component in Masson's trichrome.