Which chemical is NOT listed as an additive fixative?

• A. Acetone
• B. Mercuric chloride
• C. Picric acid
• D. Formaldehyde

Answer: (A)

Additive fixatives work by introducing a chemical substance that becomes part of the tissue’s preservation, often by binding to proteins or forming insoluble complexes. Mercuric chloride and picric acid are classic examples of additives because they contribute chemical components that help fix the tissue. Formaldehyde also acts through chemical alteration of tissue proteins, often described alongside additive fixatives in many practice references. In contrast, acetone fixes primarily by dehydration: it removes water from the tissue and denatures proteins without adding an external fixative salt or metal to the tissue. Because of this dehydration mechanism rather than adding a fixing component, acetone is not listed as an additive fixative.