I. 



IN his famous investigations into the physiology of electrotonus, 

 Pfliiger, in the year 1859, submitted the changes of excitability in 

 nerves elicited by a constant current of electricity to an experi- 

 mental examination which will stand to all time as a model for 

 similar investigations, as regards both the number and variety of 

 the methods of research employed and the completeness of the 

 experimental criticism. As test-stimulus he employed partly the 

 constant current, partly the induction-shock, and in part also he 

 used chemical stimuli. The most important actual relations 

 established by this investigation are, very briefly, as follows. In 

 the region of the positive pole of the current the excitability of the 

 nerve is diminished, as well in the extrapolar as in the intrapolar 

 direction ; and the diminution attains its definite amount gradually, 

 being not so great for some moments after the current is closed 

 as it afterwards becomes. When the current is opened there 

 occurs immediately an increased excitability, which may last for 

 a longer or shorter period. In the region of the negative pole 

 of the current the excitability of the nerve is increased as well 

 in the extrapolar as in the intrapolar direction. This increase 

 occurs directly after contact is made. When contact is broken, 

 diminished excitability is exhibited if the current is weak or 

 moderate, which, however, after an exceedingly brief interval 

 gives place to a condition of increased excitability lasting a 

 longer or shorter time. 



It is at the poles that the change in excitability is greatest, 

 diminishing as we leave these both in the extrapolar and intra- 



