428 NERVOUS SYSTEM SPECIAL METHODS. 



ammoniacal silver nitrate-and-oxide bath as follows : Pour 5 c.c. 

 of a 20 per cent, solution of silver nitrate into a measuring cylinder 

 and add to it first 5 drops of a 40 per cent, solution of NaOH, and 

 then ammonia, drop by drop, until the brown precipitate formed 

 disappears ; dilute to 25 c.c. with distilled water, and filter through 

 paper washed with the same water. 



For staining take sections one by one from the silver nitrate bath, 

 quickly wash them in distilled water and transfer them into the 

 ammoniacal silver bath. Here they remain for about ten minutes 

 when they become yellowish-brown and should be, once more, 

 quickly washed in distilled water and placed in 20 per cent, formalin 

 prepared with spring water. The reduction takes place immediately, 

 and if one works with a number of sections it is advisable to re- 

 transfer them into a fresh bath of 20 per cent, formalin. 



At the end of half an hour and even less, the reduction can be 

 considered as accomplished and sections can be washed in distilled 

 water and toned with a diluted (0-2 per cent.) solution of gold 

 chloride. This may be slightly acidified with acetic acid if one 

 wishes to obtain a faintly purple background, or neutralised with a 

 few drops of a diluted solution of sodium or lithium carbonate if one 

 prefers greyish- white backgrounds. Instead of gold chloride one 

 can use a slightly acid solution of chloroplatinic acid. After toning 

 there remains only the washing once more of sections in distilled 

 water, and the passing of them for a few minutes in a 5 per cent, 

 solution of sodium hyposulphite, or any diluted fixing bath for 

 photographic plates. Wash again, dehydrate in alcohols of increasing 

 strength up to 95 per cent., clear in carbol-xylol, and mount in balsam. 



For other details about the toning and fixing of sections see the 

 original papers of BIELSCHOWSKT (op. cit. and Journ. Psychol. Neurol., 

 iv, 19045, p. 227), as well as WOLFF (Biol. CentrU., xxv, 1905, p. 683), 

 and DA FANO (Proc. Physiol. Soc. Journ. Physiol., liii, 1920). 



Bielschowsky states that this method is also suitable for sections 

 of celloidin or paraffin blocks of formol material, but he does not 

 recommend the practice, and I have no experience of it. 



BIELSCHOWSKY'S Method for Peripheral Nerve-fibres (Journ. 

 Psychol. Neurol., iv, 19045, p. 227). This method can be applied 

 to the study of spinal and sympathetic ganglia, peripheral nerve- 

 endings, and end-organs in normal conditions, but its chief applica- 

 tions belong to the domain of histopathology. According to my 

 experience good results are rarely obtained, and the method requires 

 important modifications to become as useful as the above and 

 following ones. 



