80 THE ESSENTIALS OF HISTOLOGY 



LESSON XIX. 



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, 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 t^e 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 

 epithelioid 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 Farrant 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 sub- 

 stance, (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 Lo wit'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. 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 terminal 

 ramifications or plexuses. There are three chief kinds of special 

 organs, termed respectively Pacinian corpuscles, tactile corpuscles, and 

 end-bulbs. In the tactile corpuscles and end-bulbs the connective- 

 tissue sheath of a medullated fibre expands to form a somewhat solid 

 bulbous enlargement, which is either 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 tissue within which is generally 

 a sort of core containing numerous nucleated cells. As the nerve-fibre 

 enters the corpuscle (which in the tactile corpuscle only happens after 

 it has reached the distal part of the corpuscle having wound spirally 



1 For methods of staining with chloride of gold see Appendix. 



