Bouin’s Fixative (Bouin’s Fluid, Bouin solution)
Bouin’s fixative is the primary mordant solution, substance used to set a dye, in the trichrome stains. It is a compound fixative composed of picric acid, acetic acid and formaldehyde in an aqueous solution. Picric acid acts to balance the fixation effects of the other 2 agents.
- Acetic acid tissue swelling effect is balanced by the tissue shrinking effect of picric acid.
- Formalin causes cytoplasm to become basophilic effect is balanced by the picric acid. Good for nuclear and cytoplasmic (Stain - Haematoxylin Eosin) staining.
- Formalin causes tissue hardening effect is balanced by the soft tissue fixation of picric acid.
- Picric acid when retained interferes with some stains, including those used for blood cells.
Whole specimen fixation
- small specimens for at least 6 hours.
- other specimens can be fixed up to two days.
- large specimens can be fixed for up to three days.
Do not use Bouin’s to fix before in situ hybridisation, as then unable to detect RNA.