Buffered picric acid-formaldehyde fixative is also known by which name?

• A. Zamboni's fixative.
• B. Millonig fixative.
• C. Bouin's solution.
• D. Karnovsky fixative.

Answer: (A)

The main idea here is recognizing a fixative that uses a buffered combination of picric acid and formaldehyde. Zamboni's fixative is exactly that—a buffered picric acid-formaldehyde solution. The buffering keeps the pH near neutral, which helps preserve tissue architecture and nuclear detail better than unbuffered mixtures, while still benefiting from the rapid penetration and strong preservation provided by picric acid and formaldehyde. It presents as a yellowish solution due to the picric acid.

This name is distinct from Bouin's solution, which also uses picric acid and formaldehyde but adds acetic acid and is not buffered; and from Karnovsky fixative, which is an aldehyde-based mix (glutaraldehyde and formaldehyde) without picric acid. Millonig fixative is a different buffered fixative altogether.