30 FIXING AGENTS. 



field's haematoxylin, and treat the stained material for three to five minutes 

 with 1 per cent, chromic acid. 



40. Chromo-nitric Acid with Bichromate (KOLLMANN, Arch. f. 

 Anat. u. Phys., 1885, p. 296). 



Bichromate of potash 5 per 100. 



Chromic acid . . . . . . 2 



Concentrated nitric acid . . . . 2 



For ova of Teleostea. Fix for twelve hours, wash with water for twelve 

 hours, then remove the chorion, and put the ova into 70 per cent, alcohol. 



41. Picro-chromic Acid (Fol. Lehrb., p. 100). 



Picric acid, sol. sat. in water . . . .10 vols. 

 1 per cent, chromic acid solution . . . 25 



Water 65 



At the instant of using, you may add 0*005 of osmic acid, which makes, 

 the action more energetic. Wash with water (hot, nearly boiling water is 

 best), and then with alcohol. Fol says, "This reagent hardens tissues, 

 admirably, without hindering staining in any way ; but it is not very pene- 

 trating and fixes slowly." 



I have seen Fol's formula, with the addition: of a trace of acetic acid 

 quoted as " liquid of Hsensel " I know not with what justification. 



42. Chromic Acid and Platinic Chloride (Kernel's solution- 

 from Mitth. Zool. Stat. Neapel, 1881, p. 11). Equal volumes 

 of 1*400 solution of chromic acid and 1'400 solution of platinic 

 chloride (PtCl 4). Objects should remain in it for several 

 hours or even days, as it does not harden very rapidly. After 

 washing out with alcohol of 50 per cent. to. 70 per cent., 

 objects stain excellently, notwithstanding the admixture of ! 

 chromic acid. This is a very delicate and admirable fixative. 

 If objects that have been fixed by osmium be put into it 

 for some hours, blackening is effectually prevented. See 

 below 50. 



Salts. 



43. Bichromate and Cupric Sulphate Mixture (KULTSCHITZKY, 

 Zeit.f. wiss. Mik., iv, 3, 1887, p. 348). A saturated solution, 

 of bichromate of potash and sulphate of copper in 50 per cent, 

 alcohol, to which is added at the instant of using a little acetic 

 acid, five or six drops per 100 c.c. 



To make the solution, add the finely powdered salts to the 

 alcohol in excess, and leave them together in total darkness,. 

 for twenty-four hours. 



Fix for twelve to twenty-four hours in the dark, otherwise 

 the salts will be precipitated. Then treat with strong alcohol 

 for twelve to twenty-four hours, and make sections. 



