Strong, Rcviciv of the Golgi Method. 121 



color while the pieces become paler. For this reason the sub- 

 limate solution must be changed daily, especially at the begin- 

 ning 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 decolorized, i. e. when the tissue is complete- 

 ly freed from bichromate. If, beginning about this time, sec- 

 tions are made and examined under the microscope daily, it 

 will be noticed that the first traces of the reaction begin 3 or 4 

 days after the immersion and that they can be known by a 

 number of small black spots scattered here and there. After 

 4 or 5 days more one sees the cell-forms gradually become more 

 complete and numerous and the reaction thenceforward con- 

 tinues to extend and complete itself. It even appears that 

 further advantages are gained when the sojourn in the sublimate 

 solution is extended indefinitely, the sublimate being changed as 

 often as it becomes yellow through the presence of bichromate. 

 With brains which have been long exposed to the action of the 

 bichromate, — and such often yield the most beautiful results,- — 

 the sublimate solution must be changed during several months 

 before this yellowing ceases. 



" The above constitutes a further difference from the manner 

 of action of the silver nitrate, inasmuch as in the latter the 

 whole action is completed in 24 to 48 hours, after which no 

 further action is exerted, although the pieces can be kept in 

 it longer. 



"When the reaction has reached its maximum, the pieces 

 remain colorless and have the appearance of fresh brain tissue 

 which has been slightly washed in water. 



"The pieces may remain in the sublimate solution as long 

 as one pleases, not only on account of the possibility of a fur- 

 ther extension of the reaction but also because they thereby 

 receive a hardening better adapted for making fine sections. 



"As to the manner in which the reaction extends to the 

 different elements, I will merely remark that the reaction affects 

 the ganglion cells in pieces which have reached that degree of 

 hardening attained in the first month's immersion in bichromate 



