Fixative used for embryos?

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

Answer: (B)

Embryonic tissues are very delicate and need a fixative that penetrates quickly while preserving fine morphology. Bouin's fixative, a mixture of saturated picric acid, formaldehyde, and acetic acid, is ideal for this. The picric acid helps keep soft, delicate structures well-preserved and enhances staining; formaldehyde cross-links proteins to maintain overall architecture; and acetic acid improves preservation of nuclear detail and tissue adequacy. This combination yields excellent preservation of developing organs and cellular detail in embryos, making it a traditional and reliable choice for embryonic fixation. Be aware that the picric acid component gives a yellow coloration that must be rinsed out before processing, and the fixative is toxic, which is why its use requires careful handling. Other fixatives can cause more shrinkage, hardening, or toxicity, so Bouin's remains preferred for embryos when strong morphological preservation is needed.