REVIEW OF THE GOLGI METHOD. 81 



"The moment the pieces are brought from the bichromate 

 into the silver solution, a copious yellowish precipitate of silver 

 chromate results. The formation of this precipitate takes place, 

 of course, at the expense of the strength of the fluid, inasmuch 

 as, through the formation in loco of the insoluble precipitate, a 

 more or less considerable portion of the silver salt is deposited. 

 This changes, naturally, the relation (osmotic as well) between the 

 fluid which should penetrate into the piece and the inner portions 

 of the piece. It might happen that the whole or the greatest part 

 of the silver would be precipitated from the solution, which would 

 result in the more or less complete absence of the reaction. To 

 avoid this mishap, it is expedient to first wash the pieces in which 

 the reaction is sought in a w^eaker solution of silver. I use for 

 this purpose, from motives of economy, silver solutions which have 

 already been used on other pieces without the silver having been 

 fully neutralised. When this washing has been continued until 

 the pieces cause no more precipitate when brought into a clear 

 solution, =*' they are finally placed in the fluid of the proper strength. 

 From there on, the preparation usually requires no especial atten- 

 tion, for if the solution is present in copious quantity it is sufficient 

 to let the fluid penetrate into the interior of the piece. Yet it is 

 well to consider that it is sometimes expedient, with pieces 

 thoroughly saturated with bichromate through a long sojourn 

 therein, to change the solution for a fresh one after the pieces have 

 been in the first solution six to eight hours. This must be done 

 whenever the fluid assumes a yellow colour, which shows that the 

 silver nitrate is neutralised. In this case the reagent can no 

 longer possess the necessary strength to penetrate to the interior 

 of the pieces. 



" I have already said that this reaction, through which the 

 black staining of the elements is brought about, has nothing in 

 common with that which stains the intercellular substance under 

 the influence of light. I now need to add that it is entirely the 

 same whether the pieces in our method are kept in the light or in 

 the dark ; the reaction which is brought about through the gradual 



* Several minutes should be elapsed to test this, inasmuch as the discoloura- 

 tion of the silver solution by the reddish precipitate sometimes takes place 

 rather slowly, both in this and in the rapid method. — Author. 



