The polymer form of formaldehyde becomes active after which process?

• A. Depolymerization to formaldehyde monomer.
• B. Polymerization.
• C. Oxidation by air.
• D. Reduction.

Answer: (A)

The active fixing agent is the monomeric formaldehyde. When it’s in polymer form (paraformaldehyde) it’s relatively inert and only serves as a reservoir. Depolymerization converts the solid polymer into formaldehyde monomer, which is the species that readily reacts with proteins to form cross-links and preserve tissue structure. So the polymer becomes active after depolymerization to formaldehyde monomer.

Oxidation by air would degrade formaldehyde, not activate it; continuing to polymerize would keep it in an inactive polymer state; and reduction would produce a different, non-fixing substance, not the active aldehyde needed for fixation.