Which stain stains muscle red?

• A. Masson trichrome
• B. Van Gieson
• C. Oil Red O
• D. Mast cells

Answer: (A)

Masson trichrome is formulated to differentiate muscle from connective tissue. In this stain, the cytoplasm and muscle fibers take up the red dye (acid fuchsin/Biebrich scarlet), so muscle appears red, while collagen fibers are colored blue by the accompanying dye. This clear color separation makes it the stain that highlights muscle in red.

Van Gieson uses picric acid and acid fuchsin, which colors collagen pink/red and muscle yellow, not red. Oil Red O targets lipids and stains fat cells red, typically in frozen sections, not general muscle fibers in routine sections. Mast cells aren’t stained by this dye combination; they’re identified with other stains like toluidine blue that show metachromasia.