6 CHANGES OF EXCITABILITY IN NERVES 



polar directions. The greater the strength of the polarising 

 current, the greater is the change of excitability and its extrapolar 

 extension. Between the poles the diminution of excitability 

 extends as the strength of the polarising current increases ; or, 

 to put it otherwise, with increasing strength of current, the in- 

 difference-point moves gradually from the positive to the negative 

 pole. 



The greater the separation of the electrodes the greater is the 

 tract of nerve over which the extrapolar change of excitability 

 extends. The behaviour of the intrapolar tract is absolutely the same 

 whatever the distance between the electrodes. 



To test the local changes of excitability in the intrapolar tract 

 Pfliiger used chemical stimuli ; the induction-coil he employed only 

 to investigate the total excitability. He abstained from examining 

 the changes of excitability with sharply localised electrical stimuli 

 fearing an escape of electricity between the constant and test 

 currents. 



An important, though perhaps not unexpected, addition was 

 made to these results two years after their publication by Obernier 

 in a research carried on under Pfliiger's guidance. Obernier 

 proved by experiments that, with the application of strong polarising 

 currents (6-8 Groves), there occurs at the negative pole in the first 

 moments after contact is broken a very considerable diminution of 

 excitability 1 . 



Before this, however, attacks had been made on the correctness of 

 Pfliiger's results attacks which have since been from time to time 

 renewed by various enquirers. The most notable fact, however, is, 

 that all those who have thus assailed Pfliiger, with few exceptions, 

 have conducted their counter-researches with nothing like the same 

 care as Pfliiger employed. What Meissner says of one of the first 

 of them may be applied with justice to them all. ' Inasmuch as 

 Pfliiger has grounded all his enunciations on investigations made 

 with every kind of efficient stimulus, one has a right to demand 

 from a criticism which is directed to prove these enunciations in 

 part untenable, that it be pursued on a like basis and with a similar 

 use of every species of stimulus 2 . 



To this category of works we must refer those of Schiff 3 , of 



1 Obernier, Archiv fur Anatomic und Physiologic, 1861, pp. 268-278. 



2 Meissner, Bericht iiber die fortschritte der Anatomic und Physiologic, 1863. 

 Leipzig, 1864, p. 359. 



3 Schiff, Lehrbuch der Nerven-physiologie, Jahr 1858-59, p. 94. 



