90 THE ESSENTIALS OF HISTOLOGY. 



LESSONS XIX. AND XX. 



STRUCTURE OF GANGLIA; STRUCTURE OF NERVE-CELLS 

 OF BRAIN AND SPINAL CORD ; NEUROGLIA - CELLS ; 

 DEVELOPMENT OF NERVE - FIBRES ; WALLER! AN DE- 

 GENERATION. 



1 . PUT a small piece of spinal ganglion into 1 per cent, osmic acid for two or 

 three hours. Place it in water containing a fragment of thymol for two days 

 or more. Tease it in dilute glycerine. Notice the spheroidal ganglion-cells ; 

 their large nuclei and distinct nucleoli. Many of the cells may still be seen 

 within their nucleated membranous sheath. Look for cells which still retain 

 the axis-cylinder process and for T-shaped junctions of nerve-fibres with this. 



2. Prepare a piece of sympathetic ganglion in the same way. Cells may 

 be found with three or more axis-cylinder processes. If from a rabbit observe 

 that many of the cells are bi-nucleated. 



Measure two or three cells in each of the above preparations. 



3. Mount stained sections of ganglia in Canada balsam. These will serve 

 to show the arrangement of the cells and fibres in the ganglion and the 

 nucleated sheaths around the nerve-cells. 



4. Tease out a portion of the grey matter from a piece of spinal cord that 

 has been a day or two in dilute chromic acid ($ per cent.), or in 30 per cent, 

 alcohol. Or a little of the grey matter may, after macerating for a day or 

 two in either of the above fluids, be shaken up with water in a test tube, and 

 after standing a little while some of the sediment at the bottom of the tube 

 may be drawn off and mounted. Before covering, look for the nerve-cells 

 with a low power, and if possible get out one or two clear of the surrounding 

 substance. Mount in water with a thick hair under the cover-glass. Notice 

 the large branching cells, some with a mass of pigment near the nucleus. 

 Observe the fibrillation of the cell-processes. Notice also the reticular 

 character of the tissue in which the cells are embedded. Many axis- 

 cylinders will be seen in this preparation deprived wholly or partially of 

 their medullary sheath, and their fibrillar structure can then also be well 

 seen. Carefully sketch these appearances. To keep this preparation run 

 solution of osmic acid under the cover-glass, and when the cells are stained 

 allow a drop of glycerine to pass in by diffusion. Similar preparations are 

 to be made from the grey matter of the cerebral cortex and cerebellar cortex. 



5. Examine the nerve-cells and neuroglia-cells in sections from the spinal 

 cord, cerebrum, and cerebellum of a small animal, e.g. young rat or kitten, 

 prepared by Golgi's method. 1 The sections must be mounted in thick 



1 See Appendix. 



