Which fixative contains formalin, potassium dichromate, and mercuric chloride?

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

Answer: (A)

Fixative composition is what this item is testing. Helly fixative is the one that combines formalin with mercuric chloride and potassium dichromate, which gives rapid fixation with good preservation of cellular detail. Bouin's fixative uses picric acid with formalin and acetic acid, not mercuric chloride or chromium. Zenker's fixative contains mercuric chloride and potassium dichromate but uses acetic acid instead of formalin. Carnoy's fixative is ethanol, chloroform, and acetic acid, with no mercury or chromium. So the presence of all three components—formalin, mercuric chloride, and potassium dichromate—identifies Helly fixative.