PREPARING COCHLEA FOR MICROSCOPICAL INVESTIGATION. 383 



Slid. Gold staining. For this purpose I have found a 

 modification of Bastian's process the most advantageous. 



Place the sections in a one fifth per cent, solution of 

 chloride of gold, allow them to remain in this about half an 

 hour, then remove and wash. Lastly, place them in a solu- 

 tion containing one part of ordinary formic acid and one part 

 of methylated spirits, and in twelve hours or more the gold 

 will be reduced, the sections becoming purple or violet. 



To hasten the process the temperature should be raised a 

 little over 100° Fahr., and then the reduction may take 

 place in two or three hours. 



Mounting the sections. — They may be either mounted in 

 fluids, as glycerine, a solution of acetate of potash. Sec, or in 

 resins, as Canada balsam and gum dammar. 



For general purposes the fluids are decidedly preferable, 

 because the resins make the tissues too transparent ; how- 

 ever, if the sections be highly stained and mounted in dammar, 

 they show very nicely the various parts of the central canal 

 of the cochlea and the membrane of Reissner in sitU, especially 

 under a low power. 



Of the fluids, I prefer a solution of acetate of potash pre- 

 pared as follows : 



Acetate of potash 2 oz. 

 Spirits of camphor 30 drops. 

 Hot water 1 oz. 



E.ub down the acetate of potash in a mortar, dissolve in 

 the water, add the spirit of camphor when cold, and filter 

 carefully. Thus prepared, the solution should be quite clear 

 and rather syrupy. 



This has the advantage over glycerine in not rendering 

 the tissue so transparent, in being more easily cleaned up, 

 and in not oozing through the mounting varnish so readily. 



Before mounting it is necessary to soften the gum of the 

 section in water ; this has to be done very carefully lest the 

 swelling up of the gum or its being washed aAvay should dis- 

 place the structure too much. I say too much, because it is 

 rarely possible to avoid some displacement, and, moreover, 

 in moderation it is frequently advantageous. In those cases 

 in which staining agents have been employed the gum is 

 usually all washed away. 



I have generally found it better to make a cell on the 

 glass by means of some varnish, and then mount as follows : 



Place the section in the middle of the cell with the 

 modiolus across the slide, not in its long axis, remove the 

 excess of moisture, then add a drop of the camphorated solu- 

 tion of acetate of potash, put on a covering glass with forceps. 



