What is in Helly fixative?

• A. Formaldehyde, mercuric chloride, potassium dichromate
• B. Formaldehyde, mercuric chloride
• C. Formaldehyde, potassium dichromate
• D. Mercuric chloride, potassium dichromate

Answer: (A)

Helly fixative is a formalin-based fixative that uses a combination of heavy metals to improve tissue preservation and nuclear detail. It contains formaldehyde (from formalin) to crosslink proteins and lock structures in place, mercuric chloride to enhance preservation of morphology and nuclear details, and potassium dichromate to aid fixation and stabilize delicate components. This trio—formaldehyde, mercuric chloride, and potassium dichromate—gives Helly fixative its characteristic fixation quality. If any one of these components is missing, the fixative won’t have the same fixing properties, which is why the full combination is the correct choice.