Hematoxylin substitutes: fluorone black and methyl fluorone black (9-phenyl- and 9-methyl-2,3,7-trihydroxy-6-fluorone) as metachrome iron alum mordant dyes.

The phenyl and methyl trihydroxyfluorones, hitherto used histologically only in the rather difficult and unreliable Turchini technics for discriminating deoxyribonucleic from ribonucleic acid, find a new use as iron mordant metachrome dyes which act as nuclear stains. Nuclear staining is unaffected by acid extraction of nucleic acids, as with hematoxylin lakes. The two dyes, named by Liebermann and Lindenbaum 9-phenyl-2, 3, 7-trihydroxy-6-fluorone, have also acquired (illustrating with the phenyl homolog) longer chemical names of the form 2,6,7-trihydroxy-9-phenylisoxanthene-3-one (Eastman). Aldrich and Pfalz-Bauer adhere to the Liebermann-Lindenbaum nomenclature. The trivial name fluorone black is proposed for the phenyl homolog and methyl fluorone black for the methyl homolog. The iron lake of fluorone black appears to be a useful substitute for iron hematoxylin, methyl flurone black less useful. Neither dye has the diverse capability of hematoxylin.