540 TROPHIC CENTRES AND MODIFYING CONDITIONS. 



motorial end-plates, beginning first in the non-raedullated branches, then in the terminal 

 fibrils, and lastly in the nerve-trunks (Gcsslcr). 



Regeneration of Nerves. In order that regeneration of a divided nerve may take place 

 {Cruickshank', 1795), the divided ends of the nerve must be brought into contact ( 244). In 

 man this is done by means of sutures. About the middle of the fourth week, small clear 

 bands appear within the neurilemma, winding between the nuclei and the remains of the 

 myelin (E). They soon become wider, and receive myelin with incisures, and nodes, and a 

 sheath of Schwann (2nd to 3rd month F). The regeneration process takes place in each 

 interannular segment, while the individual segments unite end to end at the nodes of Ranvier 

 ( 321, I., 5). On this view, each nerve-segment of the fibre corresponds to a "cell-unit" 

 (E. Neumann, Ekhhorst). The same process occurs in nerves ligatured in their course. Several 

 new films may be formed within one old nerve-sheath. The divided axis-cylinders of the 

 mitral end of the nerve begin to grow about the 14th day, until they meet the newly formed 

 ones, with which they unite. 



[Primary and Secondary Nerve Suture. Numerous experiments on animals and man have 

 established the fact that, immediate or primary suture of a nerve, after it is divided, either 

 accidentally, or intentionally, hastens reunion and regeneration, and accelerates the restoration 

 of function. Secondary suture, i.e., bringing the ends together long after the nerve has been 

 divided, has been practised with success. Surgeons have recorded cases where the function 

 was restored after division had taken place for 3 to 16 months, and even longer, and in most 

 cases the sensibility was restored first, the average time being 2 to 4 weeks. Motion is 

 recovered much later. The ends of the nerve should be stitched to each other with catgut, 

 the muscles at the same time being kept from becoming atrophied by electrical stimulation and 

 the systematic use of massage ( 307). After suture of a nerve, conductivity is restored in the 

 rabbit in 40 days, on the 31st in dogs, and 25th in fowls, but after simple division without 

 suture, not till the 60th day in the rabbit. Transplantation of nerve does not succeed {John- 

 son). ] 



Union of Nerves. The central end of a divided motor nerve may unite with the peripheral 

 end of another, and still conduct impulses (Rava). [It is stated that sensory fibres will 

 reunite with sensory fibres, and motor fibres with motor fibres, and the regenerated 

 nerve will, in the former case, conduct sensory impulses, and the latter motor impulses. 

 There is very considerable diversity of opinion, however, as to the regeneration or union 

 of sensory with motor fibres. Paul Bert made the following experiment : He stitched the 

 tail of a rat into the animal's back, and after union had taken place, he cut the tail from the 

 body at the root, so that the tail, as it were, grew out of the animal's back, broad end upper- 

 most. On irritating the end of the tail, which was formerly the root, the animal gave signs 

 of pain. This experiment was devised by Bert to try to show that nerve-fibres can conduct 

 impulses in both directions. One of two things must have occurred. Either the motor fibres, 

 which normally carried impulses down the tail, now convey them in the opposite direction, 

 and convey them to sensory fibres with which they have united ; or the sensory fibres, which 

 normally conducted impulses from the tip upwards, now carry them in the opposite direction. 

 If the former were actually what happened, it would show that nerve-fibres of different function 

 do unite ( 349). Reichert asserts that he has succeeded in uniting the hypoglossal with the 

 villus in the dog. According to Gessler the end-plate is the first to regenerate.] 



Trophic Centres. The regeneration of the nerves seems to take place under the 

 influence of the nerve-centres, which act as their nutritive, or trophic centres. 

 Nerves permanently separated from these centres never regenerate. 



During the regeneration of a mixed nerve, sensibility is restored first, subsequently 

 voluntary motion, and lastly, the movements of the muscles, when their motor 

 nerves are stimulated directly (Schif, Erb, v. Ziemssen). 



Wallerian Method of Investigation. As the peripheral end of a nerve undergoes degenera- 

 tion after section, we use this method for determining the course of nerve-fibres in a complex 

 arrangement of nerves. The course of special nerve-fibres may be ascertained by tracing the 

 degeueration tract ( Waller). If after section, reunion or regeneration of a motor nerve does 

 not take place, the muscle supplied by this nerve ultimately undergoes fatty degeneration. 



5. Modifying Conditions. Under the action of various operations, e.g., compress- 

 ing a nerve [so as not absolutely to sever the physiological continuity], it has been 

 found that voluntary impulses or stimuli applied above the compressed spot, give 

 rise to impulses which are conducted through the nerve, and in the case of a motor 

 nerve, cause contraction of the muscles, whilst the excitability of the parts beloio 

 the injured spot is greatly diminished (Schiff). In a similar manner, it is found 

 that the nerves of animals poisoned with C0 2 , curara or coniin, sometimes even 

 the nerves of paralysed limbs in man, are not excitable to direct stimuli, while they 



