Clarke’s fluid is a rapid fixative, and a 1-2 mm piece of tissue will usually be fixed within an hour or two, dehydration taking place at the same time. It is generally considered to be better than Carnoy’s fluid for general morphology, with good nuclear preservation. It is suitable for smears.

It is often used to fix cryostat sections for rapid diagnosis after they have been picked up on slides and before staining with H&E. One minute is usually adequate for this. Sections are either placed into the fixative before drying, or air dried then placed in the fixative. Either appears to be satisfactory.

Time

A few hours.

Aftertreatment

Transfer to absolute ethanol.