82 REVIEW OF THE GOLGI METHOD. 



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 water 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 

 twenty-four to thirty hours ; in exceptional cases forty-eight hours. 

 The period of twenty-four to thirty hours must form the rule, 

 although, when the time of hardening has been correcdy hit upon, 

 the reaction may be well advanced in two to three 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 exceptional cases, when it 

 is best to leave the pieces forty-eight 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 

 microscopical examination of some superficial sections 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 neutralised. 



" 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, this is a 

 suitable means of preservation for pieces destined for a particular 

 investigation of long duration. 



" One of the most interesting peculiarities of the process 

 which I here describe consists in the fact that, while the brownish 

 black stain acts quite similarly upon all elements of the nervous 

 tissue (various kinds of ganglion cells, nerve-fibres, elements of 

 neuroglia, and walls of vessels), yet in reality the staining of all 

 these at one time forms an exception — />., when the elements are 

 in a certain state of hardening which one only happens upon 

 accidentally in a great number of trials. As a rule, the reaction 

 appears only partially — i.e.^ it affects only one or another layer 

 with gradations and combinations which one may term endless. 



"This peculiarity does not detract from the method, but is 

 rather among its advantages, for if the reaction affected all kinds 



