Which fixative is described as the most rapid in action?

• A. Bouin's
• B. Carnoy's
• C. Mercuric chloride
• D. Lead fixatives

Answer: (B)

Carnoy's fixative is described as the most rapid in action because its non-aqueous mix penetrates tissue quickly and causes immediate protein precipitation. The combination of absolute ethanol, chloroform, and acetic acid dehydrates, enhances penetration, and rapidly coagulates cellular proteins, so fixation occurs almost on contact. This rapid action contrasts with fixatives that rely more on slower cross-linking or aqueous chemistry. Bouin's fixes well and preserves delicate structures, but its mechanism depends more on formalin cross-linking, which takes a bit longer. Mercury-containing fixatives can be very fast and give excellent nuclear detail, but their toxicity and other practical factors make Carnoy's the standard reference for the fastest fixation in routine descriptions. Lead fixatives are not typically described as the quickest options.