Method for Demonstration cf the Golgi Apparattis. 159 



3. Reduction. 



The pieces are quickly washed twice in distilled water, and 

 further recut so that their thickness does not exceed 2 mm. They 

 are then transferred into Cajal's reducing fluid to be freshly 

 prepared every time : — 



Hydroquinone ...... l"5--2 grms. 



Anhydrous sodium sulphite . . . 0' 15-0 -25 grms. 



Distilled water ...... 100 c.c. 



Formalin ....... 6 c.c. 



First dissolve the hydroquinone in water and then the sodium 

 sulphite before adding the formalin, to be neutralized only if 

 strongly acid, as pointed out before. Instead of hydroquinone, 

 pyrogallic acid may be used, though it appears to have a lesser 

 power of penetration, and the pieces must consequently be smaller. 

 Its use may be of some advantage if only a dark brown colour of 

 the apparatus is desirable. Pieces are generally left in the reduc- 

 ing fluid from one day to the next. A longer stay, though harmless, 

 is without purpose, as after about twelve hours the A glSTOg appears 

 to be completely reduced. Weaker solutions of hydroquinone are 

 to be used only in special cases. Various attempts have been 

 made to leave the pieces in the reducing fluid a few hours only, 

 but either no special results have been obtained, or, in contradic- 

 tion to Caiieton's statement, the staining of the apparatus was 

 insufficient in consequence of a probably incomplete reduction of 

 the silver. 



4. Embedding, Toning and Counterstaining. 



The reduction having taken, place, the method is ended, and 

 the pieces may be washed in distilled water for a little while to 

 extract the formalin, and cut by means of a freezing microtome. 

 It is, however, preferable to pass them rapidly through alcohols of 

 increasing strength, clear them by means of fluid cedar-wood oil, 

 and embed them in paraffin melting at 48° C. They may also be 

 embedded in celloidin, but rapidly, because absolute alcohol and 

 ether have a tendency to dissolve the unstable reduced silver. 

 Moreover, celloidin blocks must be cut as soon as possible, while 

 paraffin blocks keep indefinitely, and may be cut, eventually in 

 series, when most convenient. The sections, however obtained, 

 free or stuck to slides, are mounted in Canada balsam or xylol- 

 colophonium in the usual way. They show the apparatus stained 

 black or dark brown on a more or less intense yellow or buff 

 background. These preparations do not generally keep well, 

 because the xylol of the balsam very often dissolves the reduced 

 silver. Further, in most cases a counterstaining is desirable. For 



