Which fixative contains paraformaldehyde?

• A. Zamboni
• B. Orth
• C. Zenker
• D. B-5

Answer: (A)

Paraformaldehyde is the solid, polymer form of formaldehyde that, when dissolved, releases formaldehyde to cross-link proteins and preserve tissue structure. Fixatives that include paraformaldehyde are chosen to provide gentle, uniform cross-linking while often better preserving antigenicity for techniques like immunohistochemistry.

Zamboni’s fixative is the one that uses paraformaldehyde as the aldehyde source, giving reliable preservation of cellular detail with this cross-linking action. The other fixatives use different chemical systems: Zenker’s is mercury- and chromate-based; Orth’s is typically an alcohol-formalin mixture, not specifically paraformaldehyde polymer; Bouin’s (B-5) relies on picric acid and formalin rather than paraformaldehyde polymer. So the fixative containing paraformaldehyde is Zamboni’s.