

PRODUCED BY A CONSTANT CURRENT. 9 



deviations depend. Any how they cannot tell against Pfliiger's laws, 

 inasmuch as experiments on fresh nerves exhibited a complete 

 accordance with them, as the authors expressly state ; and assuredly 

 no significance can be attached to the adverse results given by 

 nerves damaged in every imaginable way. 



Moreover, a nerve is so delicate an organ that it is only with the 

 greatest caution that we can draw conclusions from the phenomena 

 which it presents after serious injury ; to which may be added that in 

 investigations on the changes produced in nerves by a constant 

 current a multitude of sources of error may easily disturb even the 

 best arranged and most thoroughly thought out experiments. 



Some years after, H. Munk came forward with considerations 

 adverse to Pfliiger's results, and on this ground, that the latter had 

 in his investigations not taken into consideration the internal 

 secondary resistance in nerves. Of the great work in which Munk 

 was to have presented his experiments and his new doctrine 1 there 

 has appeared only the first part, which deals with investigations on 

 the secondary resistance in nerves. The question of changes of 

 excitability evoked by the constant current Munk accordingly treats 

 of only in a provisional communication 2 . 



Introducing as he did in the path of the current so great a resist- 

 ance that the changes in resistance occurring in the course of 

 experiment became relatively insignificant, he came to quite 

 different conclusions from Pfliiger. These and the theoretical 

 view at which he has arrived he formulates in these words. ' The 

 excitation of the nerve in consequence of the electrical current 

 is due, firstly, to the direct displacement of the nerve-fluid in the 

 direction of the current, and, secondly, to the return of the fluid, 

 on interruption of the current, to those parts of the nerve from 

 which it has been displaced.' . . . . ' The muscular contraction due 

 to a given displacement of nerve-fluid is increased by a previously 

 existing displacement of the same, when both displacements are in 

 the same direction, but diminished when they are in opposite 

 directions.' 



Thus, according to Munk, the extrapolar excitability during 

 closure of a descending current, is increased at the negative pole 

 when the test-current is descending, diminished when it is ascend- 

 ing ; and so on. 



1 H. Munk, Untersuchungen iiber das Wesen der Nervenerregung, i, Leipzig, 1868. 



2 H. Munk, Archiv fur Anatomie und Physiologie, 1866, pp. 369-390. 



