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Bouin’s Fluid (Bouin’s Picro-formal-acetic)

Bouin’s Fluid

(Bouin’s Picro-formal-acetic)


Strong formalin250mL
Saturated aqueous picric acid750mL
Acetic acid, glacial50mL



This fixative should be applied for 8 – 16 hours.


Go directly to 70% ethanol. There is a suspicion that some of the protein-picric acid complexes may be water soluble, although this is often exaggerated. In any case, the picric acid discoloration is removed from the tissue more rapidly with ethanol.

Secondary fixation

Bouin’s fluid is suitable to use as a secondary fixative following formalin fixation. It is quite commonly used for secondary fixation of sections prior to staining with trichrome methods, a procedure often erroneously referred to as mordanting. As Bouin’s fluid contains no metal ions, it cannot mordant dyes. It does, however, refix the tissues and permit acid dyes to stain more intensely, which is the purpose.

Safety Note

Prior to handling any chemical, consult the Safety Data Sheet (SDS) for proper handling and safety precautions.


  1. Culling, C.F.A.,
    Handbook of Histopathological and Histochemical Techniques, Ed. 3,
    Butterworths, London, UK.
  2. Bancroft, J.D. and Stevens, A.,
    Theory and Practice of Histological Techniques, Ed. 2,
    Churchill Livingstone, Edinburgh,, UK.