280 PRACTICAL HISTOLOGY. 



scissors, placed in a drop of water on a slide, the 

 shell of bone which forms the cupola and outer wall 

 removed, and the piece of lamina spiralis examined 

 with a low power (without covering the preparation) 

 in order to learn to recognize the structures which 

 lie on it. The glass slide is then removed to the 

 dissecting microscope, and with very iine needles 

 the lamina spiralis is separated from the columella, 

 which is then rejected. Next all the parts on the 

 lamina, but especially the row of rods of Corti, to 

 which the hair-cells as a rule cling, are broken up 

 finely, -but at the same time slowly and carefully, 

 the preparation being examined now and again with 

 the highest power which it is safe to use without a 

 cover-glass. One of the chief difficulties is apt to 

 arise from portions of the tissue sticking to the 

 needles ; if this is the case, pieces of glass rod drawn 

 out to a fine point may be substituted. When the 

 more important parts have been broken up pretty 

 completely, any thick pieces of tissue unimportant 

 to the present observation, such as bits of bone, or 

 periosteum, bundles of rnedullated nerve fibres, &c., 

 should be picked out, and then a cover-glass laid on 

 and the preparation examined. To preserve either 

 preparation permanently glycerine may be allowed 

 to diffuse in at the edge of the cover-glass ;' but the 

 bichromate specimen should first be treated with a 

 drop of carmine solution, so that the elements are 

 somewhat stained, otherwise they will be rendered 

 too transparent by the glycerine. 



In this way a number of specimens may be obtained 

 from each cochlea proceeding from above, down, 

 and preparing turn after turn ; and careful sketches 

 should be made of the different structures met with, 

 and their arrangement with regard to one another. 

 It will be found that the osmic preparations serve 

 best for showing the lamina reticularis and the 

 lamina basilaris, and the bichromate preparations 

 for the hair-cells and the membrana tectoria ; the 

 other structures are almost equally well seen in both 



