Which fixative is described as non-coagulant?

• A. Formalin
• B. Acetone
• C. Ethanol
• D. Picric acid

Answer: (A)

Non-coagulant fixatives preserve tissue primarily by chemically cross-linking proteins rather than causing them to precipitate. Formalin (neutral buffered formaldehyde) fixes by forming methylene bridges between amino groups on proteins and other molecules, which stabilizes structure without creating a loose, gel-like coagulum. This cross-linking keeps cellular components in place and maintains overall morphology, which is the hallmark of a non-coagulant fixative.

In contrast, acetone and ethanol denature and precipitate proteins, leading to coagulation that hardens and can distort fine structure. Picric acid also tends to precipitate proteins, contributing to a coagulative effect. Therefore, formalin is described as non-coagulant, making it the best choice.