658 TECHNIQUE 



per cent, aqueous solution. Its preparations are not very perma- 

 nent. The chief uses of this dye are in combination with eosin as 

 a stain for blood ; as a stain for nerve cells according to the method 

 of Nissl ; and as applied to living organs as a specific stain for 

 nerve tissues after the method of Ehrlich. These methods will be 

 described below. 



Methyl Green. This dye is preferable to methylen blue as a 

 stain for fresh tissues. It is used in 2 per cent, aqueous solution 

 and applied as a progressive stain. It also enters into the composi- 

 tion of Ehrlieh's triacid mixture. It is strongly basic. 



Carmin. This valuable dye is derived from the cochineal bug, 

 and is used either as a progressive or a regressive stain. For 

 the former,, picro-carmin or alum carmin are recommended ; for the 

 latter, borax carmin is preferable. 

 Borax Garmin : 



Borax 4 grm. 



Distilled water (boiling) .... 100 cc. ; cool, filter, and add 



Carmin 3 grm. ; when dissolved, add 



70 per cent, alcohol 100 cc. 



Mix the ingredients in the above order, and after twenty-four 

 hours filter. It may be necessary to use a drop or two of ammonia 

 to complete the solution of the carmin. This is again removed by 

 evaporation. 



Tissues are to be overstained in the carmin solution, and differ- 

 entiated in acid alcohol (70 per cent, alcohol containing 0.5 to 1 per 

 cent, of hydrochloric acid) until the red color is no longer removed 

 in clouds. The sections are then well washed with several changes 

 of 95 per cent, alcohol, cleared and mounted. 

 Alum Garmin : 



Potassium alum 5 grm. 



Distilled water (hot) 100 cc. 



Carmin 1 grm. 



Mix in the order given, boil for twenty minutes, and when cold 

 filter. 



Pier o- Carmin : 



Ammonium hydrate 5 cc. 



Distilled water : 50 cc. 



Carmin 1 grm. ; when dissolved, add 



Saturated aqueous solution of . 



picric acid 50 cc. 



Expose to light and air for two days; filter. 



