Name a non-aqueous fixative.

• A. Carnoy
• B. Formalin
• C. Bouin's solution
• D. Mercuric chloride

Answer: (A)

Non-aqueous fixatives use organic solvents to preserve tissue by dehydrating and denaturing proteins without water in the fixing medium. Carnoy's fixative is the classic example: it is a methanol (or ethanol)–chloroform–acetic acid mixture. The alcohol component rapidly removes water and fixes the tissue, while chloroform helps dissolve lipids and improves penetration, and acetic acid helps preserve nuclear detail. Because water is displaced, fixation occurs quickly and yields strong nuclear preservation, which is particularly useful for cytology and delicate tissues. In contrast, the other options rely on aqueous media—formalin is an aqueous formaldehyde solution, Bouin's uses water-based components, and mercuric chloride fixatives are typically used in watery solutions—so they are not non-aqueous fixatives.