STAINING FLUIDS. 235 



carmine, carmine and indigo carmine, aniline bine and 

 aniline red. 



Picro-carmine is specially useful for staining sections 

 hardened in picric acid. It is prepared in several 

 ways : 



1. Add to a saturated solution of picric acid in water 

 a strong solution of carmine in ammonia to saturation. 



2. Evaporate the mixture to one-fifth its bulk over a 

 water bath, allow it to cool, filter from deposit, and 

 evaporate to dryness, when picro-carmine is left as a 

 crystalline powder of red-ochre colour. 



Sections can be stained in a 1 per cent, aqueous 

 solution, requiring only ten minutes for the process ; 

 wash well in distilled water, and transfer them to 

 methylated alcohol, then to absolute alcohol, after 

 which they can be made transparent by immersing in 

 oil of cloves or benzole, before mounting in balsam or 

 dammar. 1 



The carmine and indigo fluids adopted by Merbel 

 give a blue and a red stain, and are very selective. 

 To prepare the red fluid, take Carmine, 2 dr. ; borax, 

 2dr. ; distilled water, 4oz. For the blue fluid, take 

 Indigo carmine, 2dr. ; borax, 2dr. ; distilled water, 4oz. 



Mix each in a mortar, and allow it to stand, then 

 pour off the supernatant fluid. If the sections have 

 been hardened in chromic acid, picric acid, or a bichro- 

 mate, they must be washed in water till no tinge 

 appears. Place them in alcohol for fifteen or twenty 

 minutes, then in the two fluids mixed in equal propor- 

 tions, after which wash them in a saturated aqueous 

 eolation of oxalic acid, where they should remain a 

 rather shorter time than in the staining fluids. "When 

 sufficiently bleached, wash them in water, to get rid 

 of the acid, then pass them through spirit and oil of 

 cloves, and mount in balsam or dammar. 



To summarize Mr. Groves' recommendations: 



1. Let the material be quite fresh. 



2. a. Take care that the hardening or softening fluid 



(1) See Rutherford, " Outlines of Practical Histology." Most of the stain- 

 Ing agents mentioned may be obtained of W. Martindale. chemist .10, New 

 W. 



