CHAPTER XXXII. 429 



The staining is carried out on sections of formol material in the 

 same way as described above. There is only this difference that the 

 staining in the ammoniacal silver bath is carried on a few minutes 

 longer, viz., until the sections have taken a decidedly brown colour, 

 after which they are washed in 10 c.c. of distilled water acidified 

 with 5 drops of acetic acid, when they acquire (sometimes in a few 

 seconds) a yellowish tinge. They should then be immediately 

 transferred into the usual 20 per cent, solution of formalin. For the 

 toning a neutral gold bath is necessary : sections should be left 

 therein until red-violet. In the finished preparations axis-cylinders 

 are black, myelin red- violet, connective tissue violet or blue-violet. 

 The washing in acidified water and the prolonged toning both answer 

 for the purpose of creating a sharp contrast between nerve fibres and 

 connective tissue fibres, which might otherwise become stained 

 almost as black as the axis-cylinders. 



Bielschowsky has also a method for central nerve-fibres. Sections 

 made by freezing from formol material are placed for twenty-four 

 hours or longer in a 4 per cent, solution of copper sulphate or 

 Weigert's mordant for neuroglia stain ( 910). After washing they 

 are placed for a few seconds in the usual ammoniacal silver bath and 

 then washed, reduced, toned and fixed as above. The preparations 

 are similar to those obtainable by the methods of Fajerstajn, 

 Strahiiber and Kaplan. 



BIELSCHOWSKY'S Method for Pieces (op. tit.). Good for peripheral 

 nerve-endings and embryonic material, and also for small specimens 

 of adult subjects. This method has been described by Bielschowsky 

 in various ways, probably because of the difficulty of giving fixed 

 rules in a case in which the greatest freedom had to be left to histo- 

 logists to adapt the method to the quality of their material and the 

 purpose of their investigations. In what follows two forms of the 

 method are described : one without and one with pyridine treatment 

 of pieces. 



A. Method for Pieces without Pyridine Treatment. --Thin slices or 

 small pieces of formol material are washed for some hours, first in 

 running tap-water and afterwards in distilled water. They are then 

 placed in a 2 per cent, solution of silver nitrate for from one to eight 

 days in the dark. The use of an incubator at 35 to 37 C. is optional. 

 After a wash in several changes of distilled water (to be prolonged 

 for some minutes up to some hours according to the length of time 

 during which pieces have been kept in the silver bath, and if in an 

 incubator or not) they are transferred into an ammoniacal solution 

 of silver nitrate prepared as in the method for sections, but diluted 



