What is in Bouin fixative?

• A. Acetic acid, formaldehyde, picric acid
• B. Formaldehyde and mercuric chloride
• C. Copper acetate and formaldehyde
• D. Acetic acid only

Answer: (A)

Bouin fixative is made from three components: acetic acid, formaldehyde, and picric acid. The picric acid portion acts as a coagulative fixative that helps preserve cytoplasmic detail; formaldehyde cross-links proteins to stabilize tissue architecture; acetic acid enhances nuclear detail and improves tissue penetration by swelling the tissue. Together they give excellent morphology for histology and staining, though the yellow color from picric acid must be washed out before staining. This combination is distinct from fixatives that use mercuric chloride or copper acetate, and it wouldn’t be correctly described as just acetic acid.