75 



LESSON XVIII. 



STRUCTURE OF NERVE-CELLS. 



1. TEASE in Fan-ant's solution or in dilute glycerine a small piece of a spinal 

 ganglion that has been preserved with osmic acid. Notice the spheroidal 

 ganglion-cells ; their large nuclei and distinct nucleolL 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 the cells are bi-micleated. 



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

 to show the arrangement of the cells and fibres in a 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.). Before covering, 

 look for the nerve-cells with a low power, ancl 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 pig- 

 ment 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 very dilute logwood solution or osmic acid tinder the cover-glass, and 

 when the cells are stained allow a drop of glycerine to pass in by diffusion. 



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



Nerve-cells only occur in the grey matter of the nerve-centres, and 

 in little groups on the course of certain of the peripheral nerves, these 

 groups often causing nodular enlargements of the nerves, which are 

 known as ganglia. The most important ganglia are those which are 

 found upon the posterior roots of the spinal nerves, upon the roots of 

 some of the cranial nerves, and upon the trunk and principal branches 

 of the sympathetic nerve. Minute ganglia are also found very nume- 

 rously in connection with the nerves which are supplied to involuntary 

 muscular tissue, as in the heart, alimentary canal, bladder, uterus, &c. 



Nerve-cells vary much in size and shape ; they are mostly large, 

 some being amongst the largest cells met with in the body, but 

 others are quite small. The nucleus is generally large, clear, and 



