On the nature of Romanowsky dyes and the Romanowsky-Giemsa effect

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Abstract
This paper reviews the nature of Romanowsky staining and the relationship between Romanowsky dyes and the Romanowsky-Giemsa effect (RGE). On blood and bone marrow smears the RGE is characterized by a purple colouration of nuclei and neutrophil granules. The nuclear purple contrasts strongly with the blue cytoplasmic staining of cells rich in RNA. Requirement for the occurrence of RGE are: I A cationic dye: The best dye is azure B and, though azure A gives the nuclear purple colour, the cytoplasmic blue is inferior. No other cationic dye such as methylene blue is suitable. 2 An anionic dye: Most commonly eosin Y is used, but it can be replaced by the erythrosins. Full halogenation of the fluorescein (four atoms of bromine or iodine) is not necessary. Phloxine and rose bengal are unsuitable. 3 An appropriate substrate: These are proteins with acidic side groups or proteins bound to a polyanion. For the interaction with the dyes substrates must provide a suitable three-dimensional network which is why the RGE is not obtained in solutions. A tentative theory of RGE is advanced and briefly discussed.