168 NUCLEAR STAINS WITH COAL-TAR DYES. 



for two or three minutes, until they become black. They are then 

 differentiated with neutral alcohol, until they turn grey, and are 

 then finally differentiated with clove oil. 



By this process, in resting nuclei the nucleoli alone are stained, or 

 the chromatin if stained is pale ; in dividing nuclei the chromatin is 

 stained with great intensity, being nearly black in the equatorial 

 stage. 



Gentian violet is an exceedingly powerful stain, quite as precise 

 as safranin. 



The stain keeps well. It is more or less dichroic, possibly owing 

 to the fact that the dye is not a pure substance, but a mixture of 

 " Krystallviolett " and methyl violet. 



HERMANN (Arch. mik. Anat., xxxiv, 1889, p. 58) first stains for twenty- 

 four hours or more in safranin, differentiates incompletely with alcohol, 

 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 absolute alcohol. 



288. Thionin. The hvdrochloride of thionin, or violet of Lauth, 



/ 



is a colour chemically nearly allied to methylen blue. 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 anything but the chro- 

 matin 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 resistant to alcohol that there is no risk what- 

 ever of over-shooting 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. wiss. Mik., xv, 1899, p. 312) says that, 

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

 phonium or balsam melted over a flame. FELIZAT and BRANCA (Journ. 

 Anat. Pliijs., xxxiv, 1898, p. 590) mount without a cover. HENNEGUY 

 (in litt.) clears with acetone. 



KING (Anat. Record, iv, 1910, p. 236) stains with a saturated solution 

 in carbolic acid of 1 per cent., and finds the stain permanent. 



NICOLLE'S ' tlwonine pheniquee ' consists of 1 part of saturated 

 solution in alcohol of 50 per cent., and 5 parts of 2 per cent, aqueous 

 solution of carbolic acid. 



