162 NUCLEAR STAINS WITH COAL-TAR DYES. 



of the colour is retained on the filter). The addition to them of 

 carbolic acid has been recommended (vide Journ. Roy. Mic. Soc., 

 1886, p. 908). Bismarck brown stains rapidly, but never over- 

 stains. The stain is permanent both in balsam and in glycerin. 



This colour may be used as a chromatin stain for fresh tissues in 

 the same way as methyl green. HERLA (Arch. Bid., xiii, 1893, 

 p. 423) employs for ova of Ascaris a mixture of 0-25 parts vesuvin, 

 0-25 malachite green, 10 of glycerin and 100 of water, and w r ashes 

 out with weak glycerin. 



The chief use of this colour is for progressive staining ; but it may 

 be employed for staining by the regressive method (see 289), and 

 also for intra-vitam staining ( 208) (for this purpose it is necessary 

 to see that the colour employed be pure and neutral). 



278. Methyl Violet (Methylanilin Violet, Anilin Violet, Paris Violet). 

 GRASER (Deutsche Zeit. Ghirurgie, xxvii, 1888, pp. 538 584 ; Zeit. wiss. 

 Mik., v, 3, 1888, p. 378) stains sections from twelve to twenty-four 

 hours in a solution so dilute that at the end of that time the sections 

 will have taken up all the colour from the liquid. They are then washed 

 out for a short time in acidulated alcohol, and then in pure alcohol. 

 The method is applicable to objects fixed in Flemming's mixture. 



279. Other Progressive Stains. Most of the basic tar colours used 

 for regressive staining will also give by the progressive method a nuclear 

 stain of greater or less purity if used in solutions acidified with acetic 

 acid. Amongst these may be mentioned thionin, which need not even 

 be acidified ; also, for fresh tissues especially, gentian violet, dahlia, and 

 toluidin blue. 



B. Regressive Stains. 



280. The Practice of Regressive Staining : The Staining Bath. 



Sections only, or material that is thin enough to behave like sections, 

 such as some membranes, can be stained by this method. 



The solutions employed are made with alcohol, water, or anilin, 

 or sometimes other menstrua, according to the solubility of the 

 colour. There seems to be no special object in making them with 

 alcohol if water will suffice, the great object being to get as strong 

 a solution as possible. Indeed, the solutions made with strong 

 alcohol are found not to give quite such good results as those made 

 with water or weak alcohol. Alcohol of 50 per cent, strength, 

 however, may be said to constitute a very generally desirable 

 medium. The sections must be very thoroughly stained in the solu- 

 tion. As a general rule they cannot be left too long in the staining 

 fluid. With the powerful solutions obtained with anilin a few 

 minutes or half an hour will usually suffice, but to be on the safe side 



