232 THE MICROSCOPE. 



solution of acetic acid is coloured by the addition o 

 1*3 of its volume of logwood solution. 



The aniline dyes, whether in aqueous or alcoholic 

 Solutions, give good results, and are prepared as follows r 

 B/oseanilin or magenta (Igr. to loz. of alcohol), red ; 

 Acetate of mauvein (4gr., alcohol loz., acid nitric 2 

 drops), blue; aniline black (2gr., water loz.), grey- 

 black; Nicholson's soluble blue (l-6gr., alcohol loz~ 

 and nitric 2m.), blue. 



These stains should be used weak; and specially 

 observe that after sections are stained they should be 

 passed through alcohol and oil of cloves as rapidly a& 

 possible ; otherwise, the colour will dissolve out before- 

 they can be mounted in balsam. 



Heidenhain, speaking of the use of aniline dyes r 

 gays : " The sections, upon removal from alcohol, 

 should remain for a day in a four per cent, neutral 

 aqueous solution, in a moist place, and then be imme- 

 diately mounted in glycerine and cemented." 



Some aniline dyes are but sparingly soluble in alco- 

 hol, whereas they dissolve readily in water. Their 

 colour is increased by acetic acid, and removed by am- 

 monia. There are, however, exceptions. Use benzole- 

 for clearing instead of clove oil ; this fixes the colours; 

 better, but it has a tendency to produce shrinking in 

 certain structures. 



The indigo carmine solution of Tiersch is a good 

 and useful blue stain for sections of brain and spinal 

 cord after they have been hardened in chromic acid; 

 it possesses one convenient quality viz., that if the 

 sections are too deeply stained, any excess of colour 

 may be removed by the action of a saturated solution- 

 of oxalic acid in alcohol. This reducing process should! 

 be used with caution. Tiersch's fluid consists of: 

 Oxalic acid, 1 part ; distilled water, 22 to 30 parts ; 

 indigo carmine, as much as the solution will take up. 

 A further dilution with alcohol may be necessary ; the 

 sections should be immersed in it from 12 to 48 hours j 

 the colour will determine the time. 



Beale's fluid is thus prepared : Carmine, lOgr. ; 

 liq. amm. fort., 30m. ; glycerine, 2oz. ; distilled water,. 



