NERVOaS SYSTEM— OYTOLOaiCAL METHODS. -399 



toning bath is here 10 c.o. of water with 2 to 3 drops ol: 1 

 per cent, gold chloride^ and 2 to 3 of acetic acid. 



BiiiLSCHowsKY [Jouru Psi/ch. Neurol., xii, 1909, p. 135 ; 

 Zeit. tuiss. Mik., xxviii, 1911, p. 226) also has a method with 

 pyridiii. Formol material, up to one cubic centimetre for 

 adult tissue, and up to 5 centimetres long for embryos, is put 

 for 3 to 4 days into pyridin, washed for some hours in 

 several changes of distilled water, and put for 3 to 5 

 days into nitrate of silver of 3 per cent, at a tempera- 

 ture of 36° C. It is then put for 24 hours into an oxide 

 bath made as follows : Precipitate 5 c.c. of 20 per cent, solu- 

 tion of silver nitrate by 5 drops of caustic soda of 40 per 

 cent., dissolve in ammonia, q. s.^ add 100 c.c. of water (and, 

 to hinder formation of precipitates in the tissues, a few drops 

 of ammonia). After this batb, wash for a couple of hours in 

 many changes of distilled water, and reduce in formol of 

 20 per cent.j dehydrate and make paraffin sections. These 

 may be toned, but there is not much gained by it. 



He also {ibid.) makes sections by the freezing method, of 

 formol material, and puts them for 24 to 48 hours into 

 pyridin, and washes them out well with water as before. 

 They are then put for 24 hours (or more) into 3 per cent, 

 solution of nitrate of silver at the normal temperature j then 

 into the oxide bath prepared as before, but with only 20 c.c. 

 of water instead of 100^ and without addition of ammonia 

 (the bath ought not to contain an excess of ammonia recog- 

 nisable by the smell). They remain in this until yellowish- 

 brown, but not more than half an hour, are well washed, and 

 reduced in formol of 20 per cent. They are then toned 

 with gold and fixed with hyposulphite as described ante. 



By these pyridin methods intra-cellular fibrils are generally 

 not so well shown as by the older method, but axis cylinders 

 come out better, and glia remains unstained. The method 

 succeeds even with material that has been for years in acid 

 formol, and gives a uniform impregnation of entire blocks 

 f tissue. 



ScHUTZ {Neurol. Zentralu,, xxvii, 1908, p. 909) finds that 

 the times given by Bielschowsky are too short — which is not 

 at all my experience. For toning, he puts the sections for 

 10 minutes into 10 c.o. of water with two drops of acetic 

 acid, then for 30 to 45 into 10 c.c. of water with three drop 



