XVIII.] NERVE-GANGLIA, NERVE-CELLS, ETC. 215 



3. Spinal Ganglion of Frog. These ganglia lie under cover of 

 the small white calcareous sacs situated on each side of the verte- 

 bral column, which are seen at once when the abdominal cavity 

 is opened and the abdominal viscera removed. Remove the white 

 chalky mass, and the greyish semi-transparent small ganglion will 

 be seen. With sharp-pointed forceps it is not difficult to tear away 

 the capsule of the white calcareous mass. These sacs contain arra- 

 gonite ; some of the crystals are large, but the smaller arragonite 

 particles when examined in water exhibit Brownian movement. 

 Treat it in the same way as directed for the frog's Gasserian 

 ganglion. 



(H) In a carefully-teased specimen (use a dissecting microscope, 

 p. 22), it is by no means difficult to find large unipolar cells, each 

 cell with a distinct hyaline capsule, and the cell itself with a 

 relatively large nucleus and well-defined nucleolus. Moreover, the 

 continuation of the body of the cell with a nerve-fibre is not 

 difficult to establish. The methylene-blue method may be used 

 (p. 222). 



4. Spinal Ganglion of a Skate. Make an interstitial injection 

 of osmic acid (2 per cent.) into such a ganglion. Stain a piece in 

 picro-carmine and tease it in glycerine. Bipolar cells are readily 

 found. Each cell shows a distinct capsule enclosing a nucleated 

 cell with a pole at either end 



continuous with a nerve-fibre 

 (fig. 199). 



5. GaSSerian Ganglion. FIG< I99 ._ B ipolar Ganglion Cell of the Spinal 



(a.) The Gasserian ganglion Ganglion of a skate, 



of a sheep does very well ; 



harden it in the same way as for spinal ganglia or in Miiller's fluid. 

 The same general arrangement of fibres and cells is seen, only the 

 cells are larger, and their protoplasm frequently contains granules 

 of a yellow pigment. Very instructive results are obtained by 

 double-staining it with eosin and haematoxylin, first with hsemato- 

 xylin and then with eosin, or use eosin-haematoxylin, and mount 

 in balsam. The nuclei are blue, the other parts reddish. If a cell 

 be isolated after interstitial injection of osmic acid, as recom- 

 mended for spinal ganglia, the cells have the form shown in 

 fig. 200. 



(6.) A fresh ganglion may be teased in salt solution. The large 

 spherical cells are readily isolated, but they usually shell out of their 

 capsule. Stain them with magenta solution. 



6. Gasserian Ganglion of Frog. Destroy the brain and spinal 

 cord of a frog, remove the lower jaw, divide the skull into two longi- 

 tudinally by a vertical incision. Tear off the mucous membrane 

 covering the roof of the mouth. From a foramen just behind the 



