166 A REVIEW OF THE GOLGI METHOD. 



Hon is required. In this case the metallic lustre of the fine parts, 

 e.g., the finest divisions of the nerve fibres, evidently affects the 

 observation unfavourably by giving the pictures a certain indis- 

 tinctness. The black stain which replaces the white-metalHc 

 brings out better the outlines of the fibres, and so increases the 

 demonstrative value of the preparation. 



" Inasmuch as the impregnation consists of metallic mercury, 

 the transformation of the metallic white into deep black can be 

 accomplished, according to the teaching of elementary chemistry, 

 by means of a number of reagents. There can serve for this 

 purpose : the sulphite and hyposulphite (particularly sodium sul- 

 phite and hyposulphite in 5 per cent, solution), the sulphide (of 

 potassium, sodium, and ammonium, the first two in i per cent, to 

 2 per cent., the third in ^ per cent, solutions), sulphuretted 

 hydrogen (one part of the saturated solution and three parts of 

 distilled water). One can also use with advantage the sulphocya- 

 nide (of potassium, sodium, ammonium, in 2 per cent, solutions). 



" The solutions of sulphite and hyposulphite, especially the 

 second, render necessary a careful watching of the preparations 

 that they are not entirely destroyed through a disappearance of 

 the metallic impregnation. 



" The sulphides (of potassium and sodium) are easier to 

 manage, but the complete preservation of the preparations is not 

 entirely certain with them. 



" The sulphocyanide acts very well in bringing into view the 

 smallest parts upon which the metallic impregnation has acted, 

 but it does not give a uniform black, only a brownish stain. 

 Besides this the cells and fibres under the action of this reagent 

 assume a punctate, almost pulverulent appearance. 



" Sulphuretted hydrogen is very disagreeable on occount of its 

 offensive smell (a peculiarity which it has in common with ammo- 

 nium sulphide), and it also has a tendency (as has the ammonium 

 sulphide) to stain those parts containing no sublimate brownish, 

 which impairs very greatly the clearness of the preparation. 



" From all these grounds, and, particularly on account of its 

 rapidity and certainty of action, on account of the intensity, uni- 

 formity, and sharpness of the black stain obtained, and on account 

 of the certain permanency of the preparations, the mixture used 



