PRODUCED BY A CONSTANT CURRENT. 33 



tractions, as also does the constant current, but only when it is 

 closed, and not when it is opened. Under the influence of the constant 

 current the contractions produced by the mechanical stimulus assume 

 their maximum directly, and keep at this strength as long as the 

 current is closed. When it is opened they diminish till they have 

 reached their former grade. Under the influence of the polarising 

 current the contractions remain constantly alike on repetition of the 

 experiment, although the mechanical stimulus by itself elicits even 

 weaker contractions, which gradually fall off, quite according to the 

 law established by experiments on nerve-exhaustion. 



Experiment 16. -f P = 40 ; P = 28 ; 3 Meidinger ; y = 2,2. 



a. E = 25 ; Eh. = 25. The mechanical stimulus occasions no con- 

 tractions ; the polarising current none either. Under its influence, 

 however, weak contractions are caused by the mechanical stimulus, 

 which throughout the closure of the current keep at the same height, 

 and when the current is opened straightway vanish. 



b. E = 23 ; Eh. = 119. The mechanical stimulus brings about no 

 contractions ; the constant current a make- but not a break-contraction. 

 Under its influence the mechanical stimulus causes weak contrac- 

 tions, about the same as in a ; these have a uniform height while 

 the current is closed, and vanish instantaneously when it is opened. 



c. E = 21. The mechanical stimulus by itself causes no con- 

 tractions. Under the influence of a current of the same strength 

 as in b contractions occur which are somewhat smaller than the 

 former. 



7. The extrapolar changes of excitability at the positive pole 

 of a descending current. 



The excitability of the nerve is considerably lowered. Such an 

 intensity of stimulus as but a short time previous evoked quite 

 strong muscular contractions, now produces only insignificant con- 

 tractions or none at all. In the circumstances under which I under- 

 took my experiments this diminution showed itself directly after 

 closure of the current ; at the same time the first contraction was 

 sometimes a little greater than its successors. If the current is led 

 through the nerve for some length of time the muscular contractions 

 gradually increase, but this takes place very slowly and some- 

 times scarcely appreciably, in many cases not at all. When the 

 current is opened the contractions sink to their previous height. At 

 the same time no inhibition can be demonstrated. On the contrary 

 a slight increase of excitability takes place, which is yet never of 

 consequence and is often altogether absent. 



D 



