Azure

Azure, an organic dye, is formed when methylene blue (see) is treated with alkalis (soda, 1% caustic potash, or 5-10% ammonia) due to the removal of two methyl groups from it. Thus, A., or more precisely methylene-A., is dimethylthionin chloride. A. plays an extremely important role in microtechnique, especially in the study of blood parasites, blood elements, etc. In aqueous solution, it has a blue color and stains the cell plasma orthochromatically blue, while it stains cell nuclei, fat granularity, mucus, bacterial capsules, etc. metachromatically in a red-violet color. A. is usually used in combination with eosin and methylene blue, which enhances its staining properties, and during staining, the so-called "Romanovsky effect" is obtained, which is expressed in the bright purplish-red staining of nuclei. The following preparations of A. are commercially available: A. I-pure methylene-A., A. II-a mixture of equal parts of A. I and methylene blue, A. III-eosin mixture of two neutral compounds: A. with eosin and methylene blue with eosin. All these A. are part of the Romanovsky-Giemsa azure-eosin stain. In Germany, azure is sold under the Grubler brand (Grubler, Leipzig), in the USSR it is prepared by the Institute of Pure Chemical Reagents (IREA) in Moscow. - See also Giemsa, Blood, Metachromasia.