PRODUCED BY A CONSTANT CURRENT. 15 



the perfection to which it has recently attained, seemed to offer 

 many and weighty advantages for experiments of this kind. In 

 conducting these one has not, as with electrical stimuli, to fear 

 an escape of electricity from the polarising to the test-current, or in 

 the opposite direction. One can repeat the experiments in close suc- 

 cession without the nerve being thereby rendered useless, at the 

 same time taking as measure of change of excitability individual 

 muscular contractions, and not, as with chemical stimuli, exclu- 

 sively tetanus ; and, what is perhaps most important, one can 

 get as near as one likes to the poles of the polarising current with 

 mechanical stimuli and thus investigate it more satisfactorily than 

 was ever possible with electrical or chemical stimuli. To this may 

 be added that the mechanical stimulus is so completely different in 

 its nature from the stimulus the constant current whose opera- 

 tion on the nerves it is the purpose of these investigations to 

 determine. 



Inasmuch as the changes of excitability outside the poles of 

 the polarising current had been already so many times investi- 

 gated by different enquirers, and as the results obtained in so 

 far as the methods used were free from error had invariably 

 confirmed those of Pniiger, I determined to apply myself specially 

 to the changes in excitability of the intrapolar tract, and there 

 again particularly to direct my attention to the pole nearest the 

 muscle, that is, with an ascending current to the positive, and 

 with a descending current to the negative pole, because in this 

 way results could be attained in the simplest form and with 

 least disturbance from other circumstances. At the same time 

 I did not neglect to examine also the changes of excitability at 

 other parts of the nerve, that there too I might test the correctness 

 of Pfliiger's laws by this method. My investigation separates 

 itself accordingly into the following ten divisions. 



1. The changes of excitability at the negative pole of an ascend- 

 ing current extrapolar. 



2. The changes of excitability at the positive pole of an ascending 

 current extrapolar. 



3. The changes of excitability at the negative pole of an ascend- 

 ing current intrapolar. 



4. The changes of excitability at the positive pole of an ascending 

 current intrapolar. 



