6o2 



THE NERVE CELL. 



breaches of continuity, 1 or may remain continuous. According to 

 Monckeberg and Bethe, the changes occur first near the lesion, and 

 gradually extend towards the periphery, the rate of progress varying in 

 different fibres, e.g., proceeding more rapidly in sensory than in motor 

 fibres. 2 Eventually, almost all the myelin, as well as the broken-down 

 axis cylinder, disappears, and the nerve is only represented by its 

 connective tissue sheaths and the tubes of neurolemma, which are 

 occupied by a granular multinucleated protoplasm. Within these 

 tubes fine fibres may become developed, 3 but whether _ these are of 

 a nervous nature cannot be stated; they cannot function as nerves, 

 for they are not in continuity with any other nerves or nerve 

 cells. Regeneration only occurs by an outgrowth from the central end 

 of the cut nerve fibres. Each of these appears ultimately to throw 

 out several root-like sprouts, which, unless they become entangled 

 in cicatricial tissue, tend to grow down along the sheaths of the 

 degenerated peripheral nerve fibres, and thus eventually to find their 

 way to the periphery. Probably only one of the sprouts ultimately 

 carries on the functions of the fibre, and the others disappear. The new 

 fibres become surrounded early by a thin medullary sheath, which 

 gradually becomes thicker, and a neurolemma also ultimately becomes 

 developed around them. Under the most favourable circumstances, the 

 new nerve fibres take from one to two months to become sufficiently 

 regenerated to perform their function, and cases in which a rapid 

 recovery of function has been reported to succeed nerve section, must 

 be explicable either by a duplicate source of innervation (this may 

 especially be the case with sensory nerves) or by the section having 

 been incomplete. If the observation of v. Gehuchten and Nelis upon the 

 disappearance of the sensory nerve cells of the vagal ganglion, after 

 section of their peripheral fibres, is correct, and is a phenomenon of 

 general occurrence, it is difficult to see how the sensory fibres in a cut 

 nerve ever become regenerated. Restoration of function in such cases 

 may perhaps often be explained by an ingrowth of sensory nerve fibres 

 from adjacent areas of distribution. Other observers have, however, 

 not hitherto confirmed these statements so far as the spinal root 

 ganglia are concerned ; indeed, the cells of these ganglia are stated to 

 show rather less change after section of their nerves than do the 

 anterior horn cells of the spinal cord. 



No clear evidence has been obtained in mammals of regeneration of 

 nerve fibres within the nerve centres, after artificially produced lesions. 4 

 A priori, one would expect such regeneration to occur, and certain 

 observations seem to indicate a commencement of regeneration, 5 but 

 it is never completed. Probably the cicatricial tissue offers an insuper- 

 able obstacle to the growth of the sprouting fibres. Some regenera- 

 tion of severed posterior root-fibres may occur, 6 but it does not appear 

 to extend into the posterior column of the spinal cord. Sherrington 7 

 found in the central stump fine medullated fibres, resembling those 



1 Ranvier, " Traite technique " ; Beer, Jahrb. f. Psychlat., 1893, Bd. xi. 



2 Monckeberg and Bethe, loc. cit. 



3 R. Kennedy, Phil. Trans., London, 1897, vol. clxxxviii. B. p. 257. 



4 Sherrington, Juum. Physiol., Cambridge and London, 1893, vol. xiv. p. 2/1. 

 5 Eichhorst and Naunyn, Arch. f. exper. Path. u. Pharmacol., Leipzig, 1874, Bd. n. 



S 377 



6 Kahler, Prag. med. Wchnschr., 1884, S. 301 ; Chipault, "Etudes de chir. nnkhillaire," 



Taris, 1893. 



7 Journ. Physiol., Cambridge and London, 1894, vol. xvii. p. 218. 



