I20 Journal of Comparative Neurology. 



essary therefore to make a careful preliminary injection of 

 bichromate solution so that the reagent is well distributed 

 throughout the organ. 



"A few days (6 to 8 or less) sojourn in the bichromate 

 solution is sufficient to obtain, by putting the pieces into subli- 

 mate solution, an extended fine black stain of a greater or less 

 number of cells (indeed one can obtain an indication of the reac- 

 tion on the fresh brain which is placed immediately in the subli- 

 mate solution). A more suitable period to obtain fine and 

 extended results is from 20 to 30 days. A much longer hard- 

 ening (from 2, 3, 4 months or more) is by no means unfavorable 

 for the reaction. I remember, among other cases, to have 

 obtained reactions of wonderful fineness in some whole brains 

 which were in bichromate solution nearly a whole year. 



" It will be perceived that this indefiniteness of the time 

 constitutes a very advantageous circumstance since thereby 

 pieces can be employed which would otherwise be useless. 



" (b) Transference of the pieces into the sublimate solution. 

 The solution used by me contains i/^ ^, of bichloride of mer- 

 cury. I have satisfied myself that the method is equally suc- 

 cessful when the solution is weaker {%%) or stronger (i ^). 

 The pieces are brought immediately from the bichromate into 

 this solution. 



" The reaction throughout the thickness of the piece results 

 much more slowly than with the silver nitrate. If the pieces 

 are suitably hardened, 24 to 48 hours suffices with the latter. 

 With the sublimate, on the other hand, not less than 8 to 10 

 days are necessary, in order that the reagent may penetrate 

 throughout the piece, when the pieces are small and much more 

 (2 months and upwards) when the pieces are large (whole 

 brains). The period of action of the bichromate must also be 

 considered ; the longer this has been, the longer must be the 

 sojourn in the sublimate, but the more complete and delicate is 

 the reaction. 



" During the sojourn of the pieces in the sublimate solu- 

 tion, the bichromate with which the tissue is saturated diffuses 

 out and impairs the purity of the fluid, which assumes a yellow 



