PBODUCED BY A CONSTANT CURRENT. 25 



Experiment 5. 



+ P = 22-5 ; - P = 36 ; E = ig ; 3 Meidinger, EL = 500 ; y = 20. 



a. The mechanical stimulus generates moderately strong con- 

 tractions ; the polarising current both make- and break-contractions. 

 Under its influence the muscular contractions of the first two series 

 vanish instantaneously. Later on they no longer vanish when the 

 current is closed, but they become at once quite small and remain so 

 during the whole time the current is passing ; when the current is 

 opened they again reach their former height, but there is no further 

 rise. Even in the last series of all the contractions retain close upon 

 their original magnitude, although the number of stimulations 

 amounts to about 140. 



b. The strength of the polarising current is considerably increased 

 (3 Meidinger, Eh. = 10,000), and the nerve is stimulated somewhat 

 nearer to the muscle (E = 16). Under the influence of the current 

 the contractions completely vanish. 



c. The stimulus is brought still nearer to the muscle (E = 14), and 

 the strength of the polarising current modified till it coincides with 

 that in experiment a (3 Meidinger, R7i. = 500). No change occurs in 

 the strength of the contractions either when the current is closed or 

 when it is opened. 



3. The intrapolar changes of excitability at the negative pole 

 of an ascending current. 



With weak and moderate currents the excitability of the nerve is 

 considerably heightened. This increase appears in its full strength 

 directly after the current is closed. An intensity of stimulation, which 

 shortly before called forth only slight contractions or none, now pro- 

 duces strong ones. This increased excitability exhibits itself the whole 

 time the current is passing ; it is however noticeable, especially in the 

 case of nerves which have undergone repeated experiments accord- 

 ing to this arrangement, that with the current closed the contrac- 

 tions very slowly fall off ; the decrease is, however, unimportant, and 

 does not always occur. As soon as the current is opened the 

 contractions return to their original height. In the circumstances 

 under which I have conducted my experiments, I have not been able 

 to make out any inhibition in the period immediately following. 

 On the contrary, there is often exhibited a heightening of the 

 excitability, which, however, is never particularly great ; this too can 

 often not be clearly proved. 



During closure it is at the negative pole that the increase of 



