36 FIXING AND HARDENING AGENTS 



potash, 7 parts of 1 per cent, chromic acid, 4 parts of 2 per cent, 

 osmium tetroxide. 



This mixture keeps well. Fix for from six to twenty-four 

 hours. Wash out in running water about the same time. 



You can stain in iron hsematoxylin, or less well in Altmann 

 or Bend A. See § 706 for a description of mordanting after 

 Champy's fluid. This fluid is extremely useful, and we nearly 

 always use it in addition to Flemming. 



Since the addition of 0-75 per cent, to 0-9 per cent. NaCl causes 

 disintegration of this solution in about a week, the salt Champy 

 may be made up as follows. Seven parts of 3 per cent, bichromate, 

 7 parts of 1 per cent, chromic ; then add before use 4 parts of 

 2 per cent, osmium in 4 per cent. NaCl (actually 4-275 per cent.) 

 to make a Champ}^ with 0-9 per cent. NaCl. Dissolve the osmic 

 acid first, and then the NaCl. 



50. Osmic, Bichromate, and Platinic Mixture (Lindsay Johnson's 

 Mixture). 



Bichromate of potash (2-5 per cent.) . 70 parts. 



Osmic acid (2 per cent.) . . . 10 „ 



Platinum chloride (1 per cent.) . . 15 ,, 



Acetic or formic acid . . . . 5 ,, 



Henneguy, who has worked a great deal with this reagent, and 

 recommended it highly, says {Legons sur la Cellule, p. 61) that it is well 

 only to add the acetic or formic acid just before using> as it frequently 

 reduces the osmium and platinum very rapidly and energetically. 

 He finds that it contracts the more spongy sorts of protoplasm less 

 than mixture of Flemming. Lee thought highly of it — for certain 

 objects. Twelve hours is probably the optimum time for fixation. 

 Wash out in water. 



51. Platino-aceto-osmic Acid (Hermann's) Solution (Arch. Mik. 

 Anat., xxxiv, 1889, p. 58). One per cent, platinum chloride 15 parts 

 glacial acetic acid 1 part, and 2 per cent, osmic acid either 4 parts or 

 only 2 parts. Hermann found that protoplasm structures are thus 

 better preserved than with the chromic mixture. As with Flemming, 

 the optimum time is from twelve to sixteen hours. Wash out at least 

 three hours in running water. 



The after-treatment and staining should be the same as for objects 

 treated with Flemming's solution. Rengel {Zeit. iviss. Zool., Ixiii, 

 1898, p. 454) washes out for half an hour to an hour with saturated 

 aqueous sol. of picric acid, which he thinks facilitates the staining 

 especially of nuclei. 



The action of this fixative is, roughly, similar to that of Flemming's. 

 Like Flemming's, it mordants chromatin for staining with "basic" 

 colours, with which it affords equally fine nuclear stains. But, owing 

 to the platinum in it, it diminishes more than Flemming's the colora- 

 bility of tissues with " acid " colours, so that it is extremely difficult to 

 obtain good plasma stains after its action. It causes a notable shrinkage 

 in chromatin. It gives a full fixation of cytoplasm, to which it gives a 

 much more fine-grained aspect than liquid of Flemming does. 



Leaving out the acetic acid, the solution may be used for mito- 

 chondria as in § 693. 



52. Rawitz {Zeit. zviss. Mikr., xxv, 1909, p. 386) takes 4 parts of 

 Kahlbaum's Phospho-Tungstic acid, 5 of alcohol, and 1 of acetic acid, 



