Strong, Review of the Golgi Method. 107 



change the solution for a fresh one after the pieces have been 

 in the first solution 6 to 8 hours. This must be done whenever 

 the fluid assumes a yellow color, which shows that the silver 

 nitrate is neutralized. 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 en- 

 tirely 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 penetration of the silver into the interior of 

 the tissue takes place equally well in both cases. The only rule 

 relating to keeping the pieces in the silver which experience has 

 shown to be in some manner useful is that they should be kept 

 in winter in a well-heated room. I place the vessel on a table 

 which is not far from the stove of the laboratory. 



"The pieces must remain, as a rule, in the silver solution 

 for 24 to 30 hours, in exceptionable cases 48 hours. The 

 period of 24 to 30 hours must form the rule although, 

 when the time of hardening has been correctly hit upon, the 

 reaction may be well advanced in 2 to 3 hours. In such 

 cases one may say that the reaction begins immediately, at 

 least in the superficial layers, to extend gradually deeper 

 with the deeper penetration of the fluid. In the exception- 

 al cases when it is best to leave the pieces 48 hours and 

 longer in the nitrate solution and where it is well to change the 

 solution a second time, one must regulate his procedure by the 

 results of a microscopal examination of some superficial sec- 

 tions from which the condition of the reaction may be inferred. 

 Moreover one can perceive from the yellowing of the fluid, 

 whether the reagent is nearly neutralized. 



" As for the rest, it is to be remarked that an indefinite 

 sojourn of the pieces in the silver solution lasting days, weeks 

 or even months is in no way injurious to them ; on the contrary 



