NERVE 609 



dilators with cells whose axons end in the erector miiscles of the 

 hairs. Further, after section of the sympathetic above the superior 

 cervical ganglion, the post-ganglionic nerve fibres (i.e., the fibres 

 coming off from the cells of the ganglion) may also, if the opportunity 

 be favourable during regeneration, exchange their old end-organs for 

 new ones ; pilomotor fibres, for instance, finding their way into the 

 iris and becoming pupillo-dilators. 



It is a remarkable and as yet unexplained fact that regeneration 

 of the fibres of the central nervous system either does not in general 

 occur, or is exceedingly difficult to realize. It has, however, been 

 shown that regeneration of the fibres which proceed from the cells of 

 the spinal ganglia along the posterior roots into the cord may take 

 place after the roots have been cut. 



Experimental section or, in man, traumatic division or 

 compression of a nerve leads not only to its degeneration, 

 but ultimately, if regeneration of the nerve does not take 

 place, to degeneration of the muscles supplied by it as well. 

 The muscle-fibres dwindle to a quarter of their normal 

 diameter ; the stripes disappear ; the longitudinal fibrilla- 

 tion fades out ; and at length only hyaline moulds of the 

 fibres are left, filled and separated by fatty granules and 

 globules, and surrounded by engorged capillaries. Amidst 

 the general decay, the muscular fibres of the terminal 

 ' spindles,' with which the afferent nerves of muscles are 

 connected, alone remain unchanged (Sherrington). Certain 

 diseases of the cord which interfere with the cells of the 

 anterior horn cause degeneration of motor nerves, and 

 ultimately of muscles. 



Muscles whose motor nerves have been separated from their 

 trophic centres show, when a certain stage in degeneration 

 has been reached, a peculiar behaviour to electrical stimu- 

 lation, called the ' reaction of degeneration.' To the constant 

 current the muscles are more excitable, and the contraction 

 slower and more prolonged than normal. When a current, 

 either constant or induced, is passed through a normal 

 muscle, the muscular fibres may be stimulated either directly 

 or indirectly through the intra-muscular nerves. Under 

 ordinary conditions the nerves respond more readily than 

 the muscular fibres, especially to momentary stimuli like 

 induction shocks, and therefore the so-called direct stimula- 

 tion of uncurarized muscle is as a rule an indirect stimula- 



39 



