42 CHANGES OF EXCITABILITY IN NEKVES 



d. E = 21-8; 4 Meidinger, Rh. = 20,000. The nerve is stimulated 

 2mm. nearer the negative pole. The strength of the polarising 

 current is considerably raised, but still produces both make- and break- 

 contractions, though the latter are feebler than in 6 and c. Under 

 the influence of the current the muscular contractions vanish 

 instantaneously. With interruption of the current they recur, and 

 then they exhibit a distinct but gradually declining rise as compared 

 with their original height. 



e. E = 21-8 ; 4 Meidinger, Rh. = 1,880. With diminished strength 

 of current, which, however, still produces both make- and break-con- 

 tractions, there again occurs under the influence of the current a rise 

 in the height of the muscular contractions. 



These investigations have therefore sufficiently confirmed the 

 results at which Pfliiger arrived by means of electrical and chemical 

 stimulation relative to the changes generated in nerve by a constant 

 current. If a constant current is passing through an uninjured 

 nerve the following laws hold good for all the modes of excitation 

 at present available. 



The excitability of the nerve is augmented at the negative pole, as 

 well outside as inside, in whatever direction the current passes along 

 the nerve. 



The excitability of the nerve is diminished at the positive pole, as 

 well outside as inside the pole, in whatever direction the current passes 

 the nerve. 



At loth poles the change of excitability, whether inside or outside, 

 increases with the strength of the polarising current until, in con- 

 sequence of that change, the muscular contraction has either attained 

 its maximum or is completely annulled. Further changes in the ex- 

 citability of the nerve can, of course, not be proved by an alteration 

 in the magnitude of the muscular contractions. 



It is at the two poles that the change of excitability is greatest, and 

 from each of these it diminishes in both directions, i.e. both outwards 

 and inwards. 



At each pole the change of excitability extends outside the pole over 

 tracts which are greater the stronger the polarising current. 



In the intrapolar tract the indifference-point shifts from the neigh- 

 bourhood of the positive pole towards the negative pole with increasing 



