98 THE ESSENTIALS OF HISTOLOGY. 



LESSON XXI. 



MODES OF TERMINATION OF NERVE-FIBRES. 



1. SHELL out a Pacinian corpuscle from a piece of cat's mesentery which has 

 been kept for two or three days in ^ per cent, chromic acid or 30 per cent, 

 alcohol, and clear it as much as possible of adhering fat, but be careful not to 

 prick or otherwise injure the corpuscle itself. Mount in water with a 

 thick hair to prevent crushing with the cover-glass. Sketch the corpuscle 

 under a low power, and afterwards draw under a high power the part of the 

 core where the nerve enters and the part where it terminates. Notice the 

 fibrous structure of the lamellar tunics of the corpuscle and the oval nuclei 

 belonging to flattened endothelial-cells which cover the tunics. The distinct 

 lines which when seen in the fresh corpuscle are generally taken for the 

 tunics, are really the optical sections of these flattened cells. 



2. Mount in dilute .glycerine one or more sections of a rabbit's cornea 

 which has been stained with chloride of gold. Notice the arrangement in 

 plexuses of the darkly-stained nerve-fibres and fibrils, (1) in the connective- 

 tissue substance, (2) under the epithelium, and (3) between the epithelial- 

 cells. Make one or two sketches showing the arrangement of the fibrils. 



3. Spread out a small piece of muscle which has been stained with chloride 

 of gold by Lowit's method, and examine it with a low power to find the 

 nerve-fibres crossing the muscular fibres and distributed to them. 



Try and separate those parts of the muscular fibres to which nerves 

 appear to go, and mount them in glycerine. The pieces of muscle may 

 advantageously be thinned out for observation by pressure upon the cover- 

 glass. Search thoroughly for the close terminal ramifications (end-plates) 

 of the axis-cylinders immediately within the sarcolemma. 



It is rather difficult to dissociate the fibres, and much patience is some- 

 times required in searching for the nerve-terminations, but when they are 

 found the trouble is amply repaid. 1 



Modes of ending of sensory nerve-fibres. Nerve-fibres which are 

 distributed to sensory parts end either in special organs or in free 

 terminal ramifications. Within the special organs the ending is also 

 usually ramified. There are three chief kinds of special organs, termed 

 respectively Pacinian corpuscles, tactile corpuscle*, and emi-bulbs. In the 

 tactile corpuscles and end-bulbs the connective-tissue sheath of a 

 medullated fibre expands to form a solid bulbous enlargement, which is 

 cylindrical or spheroidal in the end-bulbs and ellipsoidal in the tactile 

 corpuscles. In both kinds of end-organ there is a capsule of connective- 



1 For methods of staining with chloride of gold see Appendix. The methyl-blue method 

 of Ehrlich, which is often employed to study these and other modes of nerve-termina- 

 tion, will also be found in the Appendix. 





