400 CHAPTER XXXL. 



be performed at the normal temperature instead of in an in- 

 cubator) some instructive differentiations of ganglion- cells 

 may be obtained, the processes of the cells of Purkiiije in the 

 cerebellum, for instance, being very sharply brought out ; 

 but such preparations have a tendency to after-blackening, 

 which does not happen with those that have been thoroughly 

 impregnated with the copper. 



The advantages of the improved method are that differen- 

 tiation after staining is not necessary ; that the annoying- 

 precipitates formed on the surface of the preparations by the 

 copper in the old method do not appear ; that the divers 

 manipulations are simpler and easier ; the preparations are 

 equal in beauty to those of Pal, and can be obtained with 

 greater certainty. But it is not so well applicable to series 

 of sections by WEIGEKT'S Collodion Method, 195, because 

 the sections must be thin. 



Since the first publication of this method, it has been 

 discovered (WEIGERT, Ergebnisse der Anat., iii, 1894, p. 21) 

 that preparations made as above, without differentiation in 

 the ferricyanide liquid, do not keep -well. Weigert therefore 

 now advises that they be mordanted as above with salt of 

 Seignette, which has the advantage of preventing the forma- 

 tion of precipitates on the surface of the preparations, but 

 that tJiey be also differentiated in the ferricyanide, as in the 

 1885 method. 



Modifications of Weigert' s Method. 



712. PAL'S Method (Wien. med. Jahrb., 1886; Zeit. f. wiss. 

 Mik., iv, 1, 1887, p. 92 ; Med. Jahrb., 1887, p. 589; Zeit. f. 

 iviss. Mik., 1888, p. 88). This is a chrome-lake process. 

 You proceed at first as in WEIGERT'S process, but omitt/'-ui/ 

 the coj>2>er bath, and you stain as in WEIGERT'S process. 

 After staining in the hsematoxylin solution the sections are 

 washed in water (if they are not stained of a deep blue a 

 trace of lithium carbonate must be added to the water). 

 They are then brought for twenty to thirty seconds into 

 0'25 per cent, solution of permanganate of potash, rinsed in 

 water, and brought into a decolouring solution composed 

 of ' 



