40 CHANGES OF EXCITABILITY IN NERVES 



did not depend on inhibition of excitation setting in at the negative 

 pole itself was proved by the experiments given under 9, in which 

 the nerve was stimulated directly at the negative pole, and where 

 stronger currents were applied than in the case above mentioned. 



With increasing strengths of the polarising current, therefore, 

 the condition of diminished excitability extends over a correspond- 

 ingly increasing extent of the intrapolar tract, and in the same 

 proportion the part showing increased excitability decreases. In 

 other words, as the strength of the polarising current increases, the 

 indifference -point moves from the positive toward the negative 

 pole. 



With quite weak currents the condition of diminished excitability 

 is exhibited only in the neighbourhood of the positive pole, while 

 the greater part of the intrapolar tract shows increased excitability. 

 With strong currents it is only in the immediate neighbourhood 

 of the negative pole that an increased excitability can be demon- 

 strated ; a lowered excitability presents itself over all the rest of 

 the intrapolar tract. 



EXAMPLES. 



Experiment 28. +P = 44 ; P = 23 ; E 27. 



a. 2 Meidinger, Rh. = 19,360. The mechanical stimulus produces 

 weak contractions; the constant current make- and break-contrac- 

 tions. Under the influence of the current the contractions evoked by 

 the mechanical stimulus increase considerably, and when it is opened 

 they return to their original size. 



b. 4 Meidinger, Rh. = 19,360. The polarising current occasions 

 make- and break-contractions ; under its influence the contractions 

 evoked by the mechanical stimulus show a persistent increase. When 

 the current is interrupted a slight increase of the contractions sets in. 



c. 6 Meidinger, Rh. = 19,360. The polarising current causes make- 

 and break-contractions. Through its action the muscular contrac- 

 tions are completely arrested. Traces of them are visible only for 

 a short time after the current is passed. On opening the current, 

 however, the contractions are for a time greater than before. 



d. 2 Meidinger, Rh. = 360. The polarising current produces make- 

 and break-contractions. The mechanical stimulus, which was of the 

 same strength all through the experiment, now excites no contrac- 

 tions, in consequence of exhaustion of the nerve. Under the influence 

 of the polarising current, however, contractions still show themselves, 

 though only slight ones. 



