Thionin

Thionin, a basic thionin stain (a derivative of thiodiphenylamine), is metallic, shining needles that are quite difficult to dissolve in water but easily soluble in alcohol, giving blue-violet solutions. In histological technique, Thionin occupies a prominent place due to its ability to well stain cell nuclei, the tigroid substance of nerve cells, the granules of mast cells, plasma cells, and mucus, and due to its sharply expressed metachromasia (see Mucus). Weak (0.1%) aqueous solutions are usually used, to which, according to Mayer, a little tartaric acid is added. The carbol-thionin of Nicolas (carbol-thionin) is often used, obtained by mixing 80 cm³ of 2% carbolic water with 20 cm³ of a saturated solution of Thionin in 50% wine alcohol. Thionin also enters into the composition of complex stains: Mayer's thio-pip-ironin, Rankc's thionin-eosin, and Eisen's thionin-methylgryn-bordo. With picric acid, Thionin gives an insoluble precipitate, which gave Schmorl the occasion to recommend it for the detection of bone and tooth canals. Since Thionin is not used in wide technique, it often contains harmful impurities in sale, which strongly spoil the stain.