PRODUCED BY A CONSTANT CURRENT. 29 



again occur. When the current is opened, these for some time 

 grow more minute. Finally, they again mount so that they overstep 

 their original height not a little. When the polarising current 

 is closed, they do not altogether disappear, but merely decline to a 

 minimum. 



6. The nerve is excited with the same strength of stimulus, but 

 nearer to the positive pole (E =21). The muscular contractions are 

 now fairly strong. Under the influence of the polarising current 

 they wholly disappear, but show themselves as large as before so 

 soon as it is again opened. If the experiment is repeated in this 

 way several successive times, the muscular contractions evoked by 

 the mechanical stimulus alone become a little greater than they 

 originally were. 



5. The change of position of the indifference-point with 

 increasing strength of an ascending current. 



In order to investigate how the excitability at different points 

 of the intrapolar tract alters with varying strengths of the polaris- 

 ing current, I proceeded in the following way. I first investigated 

 Jiow a very weak current (i) changed the excitability of the nerve 

 at a spot (A) in the neighbourhood of the positive pole. If it 

 appeared that at this spot the excitability was heightened, I raised 

 the strength, of the polarising current until the excitability was 

 here visibly lowered by the current (2). Thereupon I examined 

 how the excitability was changed by the current (2) at another 

 spot () higher up. If the excitability there showed itself un- 

 changed or heightened, the strength of the current was again 

 raised till a diminution of the excitability set in. After that I 

 ascertained what relation the excitability at a spot (C) lying still 

 higher up bore to the strength of the current (3) last mentioned. 



If Pfliiger's view that with an increasing strength of current the 

 indifference-point shifts from the positive towards the negative 

 pole represented the real state of the case, the excitability at a 

 point not far from the positive pole would be raised by very 

 weak currents ; while, if the strength of the current increased, 

 a diminution of excitability would display itself at this spot, at 

 the same time that another spot lying higher up would still be in 

 the stage of increased excitability ; and so on. 



If therefore, as I gradually raised the strength of the current 

 the seat of stimulation gradually shifted from the positive to 

 the negative pole, I was necessarily in a position to prove that 



