206 CHAPTER XV. 



then stains for three to five minutes in the anilin-water gentian solution, 

 treats with the iodine solution for one to three hours, and finally differentiates 

 with alcohol. 



274. Thionin. The hydrochloride of thionin, or violet of 

 Lauth, is a colour chemically nearly allied to methylen blue. 

 It may be obtained from 'Griibler & Hollborn. I have 

 classed it here as a 'regressive stain, but its action is so 

 selective from the first that it may almost be considered to 

 be a progressive stain. ' If you stain for "only a short time (a 

 few minutes) in a concentrated aqueous solution, hardly any- 

 thing but the chromatin will be found to be stained. If the 

 staining be prolonged, plasmatic elements will begin to take 

 up the colour. After a short stain no special differentiation 

 is required ; all that is necessary is to rinse with water, 

 dehydrate, and mount. After a strong stain you differentiate 

 with alcohol in the usual way, with this advantage, that the 

 :stain is so highly resistent to alcohol that there is no risk 

 whatever of overshooting the mark ; the stain will not be 

 more extracted in an" hour" than "that of gentian or dahlia is 

 in a minute, so that the process may be controlled under the 

 microscope if desired. For this reason I think this stain 

 may be useful to beginners, but I myself prefer gentian. It 

 is a very powerful stain. 



Thionin is a specific stain for mucin, q. v. Some observers have found 

 the stain to fade. WOLFF (Zeit.f. wiss. Mik., xv, 3, 1899, p. 312) says that, 

 to avoid this, preparations should be mounted in a little solid colophonium 

 or balsam melted over a flame. 



275. Other Regressive Stains The foregoing, I think, may 

 suffice for most practical purposes, but the following may be 

 mentioned. 



Dahlia (FLEMMING, Arch. f. mik. Anat., xix, 1881, p. 

 317). The stain is paler in the nuclei than with gentian or 

 safranin. The cytoplasmic granulations of certain cells are 

 sharply stained. 



Dahlia is also a useful nuclear stain for fresh tissues (v. EHRLICH, Arch, 

 f. mil:. Anat., xiii, 1876, p. 263). For these the aqueous solution must be 

 acidulated with (7'5 per cent.) acetic acid ; or you may stain in a neutral 

 solution, and wash out with acidulated water. 



Victoria Blue (Victoriablau) (LUSTGABTEN, Med. Jahrb. k. 

 Ges. d. Aerzte zu Wien, 1886, pp. 285291). 



