Bouin solution

Bouin solution is a compound fixative used in histology. It is composed of picric acid, acetic acid and formaldehyde in an aqueous solution. It is especially good for gastrointestinal tract biopsies because this fixative allows crisper and better nuclear staining than 10% neutral-buffered formalin. It is not a good fixative when tissue ultrastructure must be preserved for electron microscopy. However, it is a good fixative when tissue structure with a soft and delicate texture must be preserved. Formalin-fixed tissue is normally mordanted with Bouin solution for better staining results in the trichrome stains. The acetic acid in this fixative lyses red blood cells and dissolves small iron and calcium deposits in tissue. A variant in which the acetic acid is replaced with formic acid can be used for both fixation of tissue and decalcification.