32 CHANGES OP EXCITABILITY IN NERVES 



increase is shown in its full amount directly after the current 

 is closed. An intensity of stimulus which previously elicited 

 very slight contractions or none, now causes very strong ones. 

 This increased excitability lasts the whole time the current is 

 passing. At the same time the muscular contractions get smaller, 

 although only to a slight extent, and often there is no diminution. 

 On the cessation of the current the contractions decline to their 

 previous size. 



In the circumstances under which my experiments were per- 

 formed no diminution of excitability set in after the current was 

 opened. A slight increase sometimes occurs, but in general the 

 contractions return to their previous height after the current is 

 opened. As long as the current is closed the rise in excitability 

 is greatest at the negative pole, and from there it falls off towards 

 the muscle. 



The stronger the polarising current the greater also is the 

 increase of excitability, and the greater the tract of nerve over 

 which it extends. 



If the experiment is repeated in such a way that closure and 

 opening succeed one another regularly, while the strength of the 

 stimulus and of the current remain constant throughout, the 

 contractions exhibited under the influence of the polarising 

 current remain steadily uniform through the whole series, even 

 though the contractions evoked by the mechanical stimulus alone 

 might gradually fall off through exhaustion of the nerve. 



EXAMPLES. 

 Experiment 14. 



+ P = 30 ; P = 17 ; E = 16 ; 3 Meidinger, Eh. = 85 ; y = 32. 



The mechanical stimulus occasions moderate contractions: the 

 constant current make- but not break-contractions. Under its 

 influence the contractions evoked by the mechanical stimulus rise 

 to about the maximum. At the same time the first contraction 

 produced after passage of the current is a little stronger than its 

 successors, which undergo an exceedingly slow decline. After the 

 current is opened the contractions return directly to abaut the same 

 height as they previously had. 



Experiment 15. 



+ P = 36 ; P = 24 ; E11-, 3 Meidinger, Rh. = 100 ; y = 15. 

 The mechanical stimulus produces very strong muscular con- 



