10 CHANGES OF EXCITABILITY IN NERVES 



To estimate the value of these conclusions is clearly impossible as 

 Munk has adduced no proofs to substantiate them. In his criticism 

 of Pfliiger he has moreover entirely overlooked the fact that the 

 latter had also obtained by means of chemical stimuli the same 

 results as he had got by testing- with an electrical stimulus ; and 

 just as little does he take into account that Bilharz and O. Nasse had 

 also found these confirmed by mechanical stimulation applied to fresh 

 nerves. Under these circumstances we cannot regard his results as 

 conclusive. 



With all possible care and observance of minutiae Hermann 1 

 examined the changes of excitability, chiefly in the intrapolar region, 

 with the object of substantiating the doctrine based on his investi- 

 gation of the action-current in polarised nerves. ' Nerve excitability,' 

 he says, ' increases in amount as we proceed to spots stronger in 

 positive, or weaker in negative polarisation ; in the reverse case it 

 diminishes.' 



In the introduction to his paper he directs attention to a cir- 

 cumstance, in itself clear enough, but which has been strangely 

 overlooked by enquirers in this subject, namely, that, as the strength 

 of the test-stimulus is increased, a point is reached where the 

 influence of the constant current on the excitability of the nerve 

 suddenly vanishes ; and this point corresponds to such a strength of 

 stimulus as evokes a maximal muscular contraction. With such a 

 strength the muscular contraction can no longer be increased by 

 katelectrotonus, for the very reason that it is at a maximum ; its 

 diminution through anelectrotonus also is trifling, and vanishes 

 with such a strength of the stimulus as exceeds by only an in- 

 significant amount that at which the maximal contraction occurs. 



Further on in his paper Hermann gives an account of the in- 

 vestigations by which he supports his own doctrine and opposes 

 Pfliiger, that is, not Pfliiger's experiments, but his theoretical 

 explanation of them. I pass over here one of Hermann's experi- 

 ments, as to which he afterwards himself discovered that the 

 result might be referred to a defect of arrangement 2 , and shall 

 only mention the others. These aim at proving : 



I. That if the polarising current along with the seats of stimu- 

 lation is brought nearer the muscle, while nothing else is altered, 

 a diminution ensues in the influence of the polarising current for 

 every stimulus applied on the near side of the indifference-point, 



1 Hermann, Archiv fur die ges. Physiologic, vii, 1873, pp. 323-364. 



2 Hermann, ib. vii, 1873, pp. 497-498. 



