A REVIEW OF THE GOLGI METHOD. 161 



more suitable period to obtain fine and extended results is from 

 20 to 30 days. A much longer hardening (from 2, 3, 4 months, 

 or more) is by no means unfavourable for the reaction. I remem- 

 ber, 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 con- 

 stitutes a very advantageous circumstance, since thereby pieces 

 can be employed which would otherwise be useless. 



"(z^) Transference of the pieces into the sublimate solution. 

 The solution used by me contains ^ per cent, of bichloride of 

 mercury. [ have satisfied myself that the method is equally suc- 

 cessful when the solution is weaker (}( per cent.), or stronger 

 (i per cent.). 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 sublimite. 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 subUmate solution, 

 the bichromate with which the tissue is saturated diffuses out and 

 impairs the purity of the fluid, which assumes a yellow colour, 

 while the pieces become paler. For this reason the sublimate 

 solution must be changed daily, especially at the beginning of the 

 immersion. Later, the changes are made only when the solution 

 becomes yellow. 



" It may be assumed that the reaction begins when the pieces 

 are entirely decolourised, i.e., when the tissue is completely freed 

 from bichromate. If, beginning about this time, sections are made 

 and examined under the microscope daily, it will be noticed that 

 the first traces of the reaction begins 3 or 4 days after the immer- 

 sion, and that they can be known by a number of small black 



