What occurs when additive fixative is used?

• A. Methylene bridges
• B. Ethanol fixation
• C. No chemical bonding occurs
• D. Proteins denature completely

Answer: (A)

When an additive fixative is used, aldehyde fixatives form covalent cross-links between tissue proteins, creating methylene bridges that connect amino groups on different molecules. This cross-linking stabilizes and preserves the cellular architecture, making the tissue less soluble during processing. Ethanol fixation works differently, relying on dehydration and precipitation rather than covalent bonding, so it does not produce those methylene bridges. Saying no chemical bonding occurs isn’t accurate for additive fixatives, since the bonds are a key feature of their action. And the idea that proteins are denatured completely isn’t correct; fixation alters structure to preserve morphology without fully denaturing all proteins.