Pyronin

Pyronin, a greenish basic aniline dye in the form of crystals, easily soluble in water and alcohol. The solution is red in color with yellow fluorescence. In microscopy, it is used mainly in combination with methyl green (Methylgrün) according to the Pappenheim-Unna method, which consists of the following. Objects are fixed in absolute alcohol, in Zënker's fluid or Maximov's fluid. When fixing with formalin, thorough washing in water is mandatory. Sections are frozen, paraffin, or celloidin; in the latter case, sections are mounted on cover slips and freed from celloidin. From water, sections are transferred to the Pappenheim-Unna solution (see Blood). Staining for 20 minutes (paraffin sections for 40 minutes) with heating. Rapidly cooled sections are rinsed for 1-3 minutes in water, dried with blotting paper; rapid differentiation in a mixture of alcohol and acetone (equal parts); xylene; balsam. Good staining for plasma cells. Also used for staining blood, bacteria, in particular gonococci. Some recommend the Pappenheim-Unna mixture for staining sections of the pancreas because at this the islets of Langerhans are very well delineated (pale against the red background of the remaining parenchyma). Unna later recommended for fixation a 2% zinc chloride solution (pieces lying for 24 hours on cotton), after which the object is transferred for a day to absolute alcohol. Celloidin embedding, and then as usual; the washing water (after staining) is slightly acidified with acetic acid, and the absolute alcohol (for differentiation) with a weak solution of trichloroacetic acid.