38 CHANGES OP EXCITABILITY IN NERVES 



their previous height. No accompanying- diminution of the excit- 

 ability can be made out. On the contrary, in many cases an in- 

 crease of the contractions sets in, which is yet never great, and 

 occasionally is not at all noticeable. The greatest diminution 

 during closure of the current takes place at the pole itself. It 

 increases with the strength of the polarising, current. If the 

 experiment is repeated time after time, other conditions being the 

 same, the diminution of excitability generally increases each time, 

 though only to a very inconsiderable extent. The contractions 

 elicited by the mechanical stimulus alone in most cases remain 

 uniform throughout the experiment. 



EXAMPLES. 



Experiment 25. + P = 39 ; P = 24-5 ; E = 36 ; 3 Meidinger, 

 Rh. = IOOO ; y = 27. 



The mechanical stimulus causes strong contractions, the polarising 

 current make- and break-contractions. Immediately after contact 

 is made the contractions sink to half their former height and remain 

 thus as long as the nerve is traversed by the current. When the 

 current is opened they regain their previous height. With repeated 

 making and breaking of contact, the contractions produced under 

 the influence of the polarising current decline gradually, whereas 

 the mechanical stimulus by itself evokes contractions of tolerably 

 uniform strength during the whole period. 



Experiment 26. -f P = 44 ; P = 24 ; E = 41 ; 3 Meidinger, 

 Rh. = 132 ; y = 33. 



a. The mechanical stimulus - occasions moderately strong contrac- 

 tions ; the polarising current make- but not break-contractions. 

 Under its influence the contractions elicited by the mechanical 

 stimulus disappear ; the moment after closure, however, there is a 

 trace of contraction. As soon as the current is opened the contrac- 

 tions exhibit their initial strength, with perhaps a slight increase. 



b. E = 39-5. Other conditions being the same, the nerve is 

 stimulated somewhat farther from the pole. If a polarising current 

 is applied of the same strength as in a, the muscular contractions fall 

 off to a considerable extent, but not so much as in a. The first con- 

 traction after the current is thrown in is a trifle greater than its 

 successors. Directly after the current ceases the contractions regain 

 their original strength. 



