156 



THE PHYSIOLOGY OF NERVE 



first of all that degenerating muscle and nerve is very sensitive to the 

 galvanic and relatively insensitive to the induced current, so that even 

 a weak constant current may produce an exaggerated contraction, or 

 galvanotonus, while strong induction shocks may fail entirely in elicit- 

 ing a response. This fact in itself is suggestive of degeneration, be- 

 cause it indicates that the irritability of this particular muscle and 

 nerve has become more nearly like that of all sluggishly reacting forms 

 of protoplasm. A further means of differentiation is furnished by the 

 so-called law of degeneration which is obtained by the same procedure 

 as the law of unipolar stimulation, the stimulating electrode being 

 applied either to the region of the muscle or to that of the nerve in- 

 nervating it (Erb's reaction). For reasons not clearly understood, de- 

 generated muscle reacts first on the making of the galvanic current 

 when the anode is the active electrode, while, on breaking, the 

 cathodic opening contraction is obtained before the anodic opening.^ 

 In advanced cases of degeneration, the galvanic excitabihty is also 

 diminished, only the first contractions remaining in evidence until 

 eventually even these disappear. The law of degeneration may be 

 tabulated as follows: 



Galvanic current 



Chilarducci has suggested to place the stimulating electrode at 

 some distance below the degenerated muscle, because a contraction 

 may then be elicited with currents three or four times weaker than 

 those ordinarily required for indirect excitation. Furthermore, con- 

 tractions may then be evoked long after the direct stimulation has 

 ceased to give positive effects. This phenomenon, which is called 

 ''reaction at a distance, " may be used for the diagnosis of degeneration 

 of long standing and unusual obscurity. 



1 Babinski, Compt. rend., 1899, 343. 



