Bismuth hematoxylin stain for arginine residues

Bismuth ions complex with hematoxylin oxidized by sodium iodate to form a dark blue dye that stains structures with high arginine content. In citrate buffer at pH 5.2, staining is confined to cell nuclei and myelin sheaths. Extraction of nucleic acids has little effect on the stain. Blockade of the guanidino groups of arginine completely abolishes staining.