Which fixative preserves erythrocytes in bone marrow sections and contains formaldehyde?

• A. Helly
• B. Zenker
• C. Bouin
• D. Carnoy

Answer: (A)

Preserving erythrocytes in bone marrow sections relies on a fixative that both fixes with formaldehyde and helps stabilize delicate red cells. Helly's fixative provides this combination: it is a formaldehyde-based solution that also contains mercuric chloride. The formaldehyde crosslinks proteins to lock cellular structures in place, while the mercuric chloride helps stabilize membranes and cytoplasmic detail, giving erythrocytes and bone marrow elements a faithful, well-preserved appearance in sections.

Other fixatives listed either lack this specific combination or use components that can alter or damage red cells. Zenker’s fixative contains mercuric chloride but not formaldehyde, so the same crosslinking balance is not achieved; Carnoy’s and Bouin’s fixatives are more aggressive acids or alcohol-based solutions that can cause dehydration, distortion, or loss of red cells, making erythrocyte preservation less reliable in marrow tissue.