What is the ratio of stock solution to acetic acid in Zenker fixative?

• A. 95 parts stock to 5 parts acetic acid
• B. 90 parts stock to 10 parts acetic acid
• C. 80 parts stock to 20 parts acetic acid
• D. 99 parts stock to 1 part acetic acid

Answer: (A)

Zenker fixative uses a large fixed component with a small amount of acetic acid added to it. The acetic acid is included in only about 5% of the final mix because it helps improve nuclear detail and penetration without causing excessive tissue swelling or distortion. That’s why the stock-to-acetic-acid ratio is 95 parts stock to 5 parts acetic acid. Using more acetic acid (like 10% or 20%) would increase swelling and artifact risk, while too little (around 1%) wouldn’t provide the nuclear-detail benefit.