Orcein

Orcein, a vegetable dye, obtained from certain lichens growing in the West Indies and on the Canary Islands (Roccella Montagnei, R. fuciformis, R. peruensis, R. tinctoria). During fermentation and under the action of ammonia, an uncolored crystalline substance orcin (syn.-dioxitoluol, dioxymethylbenzene) is obtained, which, upon oxidation in air and in the presence of ammonia, turns into O., the exact formula of which is unknown and which appears to be a mixture of various compounds. O. is a brown amorphous powder, insoluble in ether, benzene, chloroform, carbon disulfide, toluene, xylene, slightly soluble in water and 1% acetic acid, more soluble in 1% hydrochloric acid and easily soluble in 1% caustic soda (NaOH), acetone, glacial acetic acid, absolute ethyl and methyl alcohol. Application: 1) for staining nuclei and plasma (rarely) according to the formula of Israel, who introduced it into histological practice, and 2) mainly for staining elastic tissue [according to Unna's formula, 1 g of O. is dissolved in 100 cm³ of acidified with hydrochloric acid alcohol (100 cm³ of 70% alcohol and 1 cm³ of Acidi muriatici officinalis)]. The solution can be used immediately after preparation. Sections are stained for 30-60 minutes, quickly washed with 96% alcohol, differentiated in absolute alcohol until almost complete discoloration of the other tissues of the preparation, and mounted through xylene in Canadian balsam. The elastic tissue is stained in a dark brown-red color, the rest except cartilage is colorless. If it is desirable to stain the nuclei, then after staining with O., sections are washed in distilled water, stained with hematoxylin, washed in running water, and then differentiated in alcohol, starting with 70%, and then mounted according to general rules in Canadian balsam. O. is also used in mixtures with other dyes: Wasserblau-O., Wasserblau-O.-eosin (Unna), Wasserblau - orcein - eosin - acid fuchsin (Pasini), orcein-hematoxylin-acid fuchsin-picric acid (Delamare). According to Romeis, a good O. gives a more selective staining of elastic tissue than Weigert's resorcin-fuchsin. However, a pure product is found far from often, since there are many counterfeits and falsifications. The 'Orsein-Ersatz' released by German firms cannot be recommended.