BY DR. KLEIN. 83 



through which in the same animal the auditory nerve passes 

 are best suited for the purpose. If the first are used, the root 

 of the nerve with its ganglion is excised, and macerated in 

 iodized serum, dilute solution of bichromate of potash, or 

 Miiller's fluid, for twenty-four hours or more, after which the 

 cells may be teased out with needles. Good teased prepa- 

 rations can also be obtained of the ganglia of the spinal 

 nerves of fish or frogs in the fresh state. The ganglion cells 

 of fish and frogs, thus isolated, are mostly bipolar, less fre- 

 quently inultipolar. The processes exhibit fibrillar streaking, 

 and, when a process is isolated for some distance, it is found 

 to become invested with a medullary sheath at a short distance 

 from its origin ; or, in other words, it assumes the characters 

 of a medullated nerve fibre. The Schwann's sheath of this 

 nerve fibre is continuous with the similar membrane which 

 forms the capsule of the ganglion cells from which it originates, 

 and in which, as in the Schwann's sheath, there are oblong 

 nuclei at regular distances. In the ganglion cells of the Gas- 

 serian ganglion of the frog, there are always masses of yellow 

 pigment. In the spinal nerve ganglia of the mammalia, it is 

 only possible to isolate unipolar cells. Good permanent pre- 

 parations of ganglion cells may be obtained after treatment 

 with chloride of gold. With this view the Gasserian ganglion 

 of the frog, freshly excised and cut into with fine scissors, is 

 placed for ten or fifteen minutes in chloride of gold, and then 

 exposed in slightly acidulated water to daylight, until it as- 

 sumes a darkish tinge. In preparations of ganglia thus treated 

 and teased in glycerin, the ganglion cell substance, along 

 with the axis-cylinder process, is violet red, while the nucleus 

 is pale. 1 



(6) Ganglion Cells of the Brain and Spinal Cord. 

 The spinal cord of the calf or ox are the best objects for this 

 demonstration. The organ must be divided into small por- 

 tions, which must be placed in bichromate of potash solution, 

 for periods varying from a few days to several weeks. Then 

 a thin slice of gray substance is to be cut with the razor pre- 

 ferably from the anterior horns and teased in the liquid in 

 which it has been macerated. Any one who is practised in the 



1 Preparation of the Gasserian Ganglion. A frog having been 

 rendered ex-sanguine by slitting open the ventricle, the roof of the 

 skull is exposed, and then carefully raised from the occipital region for- 

 wards. This process is continued until the internal auricular foramen 

 of the petrous bone can be distinctly seen. Then the medulla ohlon- 

 gata and pons are pushed aside with a needle, and the notch of the 

 pars petrosa cleared of fluid by dabbing it with a fragment of bibulous 

 paper. The fifth nerve is then readily seen. On it, close to where it 

 enters the bone, is a distinctly yellow swelling, which must be care- 

 fully exposed by removing the portion of bone which conceals it, and 

 excised with fine scissors. 



