Anionic counterstains

INTRODUCTIONFor the study of microscopic anatomy and of pathological material, it is usual to stain sections of tissue in such a way as to impart a dark color to the nuclei of cells and a lighter, contrasting color to the cytoplasm and extracellular structures. In most of the general "oversight" methods used in histology, a blue, purple, or black nuclear stain is followed by a paler, usually pink, counterstain, which colors all the other components of the tissue. Simple counterstaining procedures using anionic dyes are considered in this article. The rationales of the techniques are discussed, but methods of higher chemical specificity (e.g., for nucleic acids, carbohydrates, and functional groups of proteins) are not covered.