36 CHANGES OF EXCITABILITY IN NERVES 



current, even when the contractions called forth by the mechanical 

 stimulus alone gradually fell off. 



EXAMPLES. 

 Experiment 19. 

 -f P = 39 ; -P = 24-5 ; J?= 27 ; 3 Meidinger, Rk. = 760 ; y = 27. 



The mechanical stimulus by itself occasions no contractions ; the 

 polarising current produces both make- and break-contractions. 

 Under its influence very strong contractions take place, which 

 remain at the same height all the time the current is closed, and 

 disappear when it is opened. 



Experiment 20. 



-f P = 44 ; P = 24 ; .Z? = 26 ; 3 Meidinger, Eh. = 132 ; y = 30. 



The mechanical stimulus causes small muscular contractions ; the 

 polarising current make- but not break-contractions. Directly after 

 the current is closed the contractions produced by the mechanical 

 stimulus become very powerful. They keep at nearly the same height 

 all the time the current is closed ; yet they do gradually fall, though 

 the decrease is very trifling. When the current is opened they 

 return to their initial magnitude ; sometimes they rise beyond this. 

 The diminution caused in the contractions is pretty much the same 

 after repeated experiments, although the contractions produced by 

 the mechanical stimulus alone gradually get weaker. 



Experiment 21. 



+ P = 44 ; -P = 26 ; E = 31 ; y = 34 ; 3 Meidinger. 



The mechanical stimulus calls forth strong contractions. The strength 

 of the polarising current is raised after each experiment. With Rh. = 

 90, the reinforcement of the contractions is still quite inconsiderable, 

 though fully apparent. The stronger the current applied, the greater 

 increase is there in the contractions as compared with those elicited 

 by the mechanical stimulus alone. This increase of excitability is 

 exhibited all the time the current is closed ; the contractions occurring 

 under its influence, however, slowly decline from the first one after 

 closure, which is the strongest. After interruption of a current of low 

 intensity they resume their former height, but with a certain strength 

 of current (Rh. = 450) and upwards a lowering of excitability sets 

 in directly after the current is opened, at first scarce recognisable, 

 but always more clearly marked as the strength of the current in- 

 creases. At the end of this diminution a moderate increase of 

 excitability takes place. 



