8o 4 NERVE 



passing down along the previous motor path to its proper muscular 

 termination, and the other passing down the sensory path. Although 

 there is no evidence that efferent fibres can unite with afferent fibres, a 

 degenerated afferent path can therefore serve as a chemiotactic scaffold- 

 ing or guide for the growth of regenerating motor axons, though not 

 such an efficient one as a degenerated motor path. Sensory fibres, 

 however, cannot regenerate along motor paths or make functional union 

 with the receptive substance of skeletal muscle. 



Regeneration of the fibres of the central nervous system either does not 

 in general occur, or is exceedingly difficult to realize. This lends support 

 to the doctrine of the importance of the neurilemma in regeneration, 

 since its elements are scantily developed in the fibres of the brain and 

 cord (p. 860) . 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, so that the normal reflexes through the res- 

 piratory, cardiac, and vaso-motor centres may be once more obtained. 



Degeneration of Muscle. 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 fibrillation 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 capil- 

 laries. Amidst the general decay, the muscular fibres of the 

 terminal ' spindles ' with which the afferent nerves of muscles arc 

 connected alone remain unchanged (Sherrington). Certain dis- 

 eases of the cord which interfere with the cells of the anterior horn 

 cause degeneration of motor nerves, and ultimately of muscles. 

 The motor nerve-endings degenerate sooner than the sensory. 

 Both may, under suitable conditions, regenerate (Huber). 



Reaction of Degeneration. 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 

 stimulation, 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 intramuscular 

 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 stimulation of uncurarized 

 muscle is as a rule an indirect stimulation. When the muscle is 

 curarized and the nerves thus eliminated, the excitability to induced 

 currents is found to be diminished. The same is the case in a muscle 

 which exhibits the reaction of degeneration after section of its motor 

 nerve, only the loss of excitability to induced currents is greater, and 

 may even be complete. The common statement that the closing anodic 

 contraction is stronger than the closing kathodic the opposite of the 

 ordinary law is subject to so many exceptions that it has no diagnostic 

 value. The nerves are inexcitable either to constant or induced 

 currents. The reaction of degeneration is only obtained from paralyzed 

 muscles when the paralyzing lesion is situated in the cells of the anterior 



