io6 Journal of Comparative Neurology. 



lution ( i^ c^ ) appears to be somewhat more suitable (giving 

 finer results though confined to fewer elements) so long as the 

 pieces have not yet reached the complete hardening, while a 

 slightly stronger solution (to i f^) appears better adapted for 

 pieces whose hardening has progressed a little too far. 



" The quantity of the silver solution to be used must vary 

 with the number and size of the pieces to be laid therein, but 

 must be relatively abundant. For two or three pieces of about 

 I ccm. I use about half a beaker {bicchierc) of the fluid. 



"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 solu- 

 tion, 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 weaker 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 neutralized. When this 

 washing has been continued until the pieces cause no more pre- 

 cipitate 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 attention, 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 



'Several minutes should elapse to test this, inasmuch as the discoloration of 

 the silver solution by the reddish precipitate sometimes takes place rather slow- 

 ly, both in this and in the rapid method. — Writer. 



