198 ELECTRO-PHYSIOLOGY CHAP. 



discussion ; i.e. the periodic waves of contraction that start from 

 the kathode of the constant current, without any apparent shift- 

 ing of the object upon the exciting electrodes. " The number 

 of contractions observed during a closure of 12 minutes was less 

 (23) with weak currents, and more (57) with stronger currents. 

 The intervals at which the waves followed varied between 4 and 

 20 sees. The periods were frequently short and equal, in 

 other cases they varied in duration. The ureter did not usually 

 relax completely at the negative electrode in the interval between 

 two waves at least with the stronger currents (persistent closure 

 contraction)." At break of the constant current again, Engelmann 

 repeatedly saw periodic waves of contraction starting from the 

 region of the positive pole in the rat's ureter (I.e. p. 414), a 

 phenomenon to which we find an analogue in the fact, that the 

 discharge of a persistent opening excitation in rhythmical single 

 twitches may also be observed in the sartorius under the 

 described conditions, though more rarely. As a rule, indeed, these 

 are only more or less extended single twitches, and it is im- 

 possible to draw any conclusion as to their tetanic character. 



No fundamental difference, therefore, obtains between the 

 manifestations observed in cardiac, and in other, striated and 

 smooth, muscle, during the constant passage of current ; and 

 it is only quantitatively that differences can be detected in 

 the rhythmical discharge of excitation, which occurs invariably 

 in the one case, and in the other only under certain con- 

 ditions. The much slower succession of single waves of contrac- 

 tion in the electrical excitation of the ureter, is easily explained 

 by the lower excitability and more sluggish reaction of smooth, 

 as compared with striated, muscle. And (as we shall see below) 

 a similar relation obtains between this last and the motor 

 nerves, so that the same manifestation presents itself in gradations 

 in the electrical excitation of smooth muscle, cardiac muscle, 

 striated skeletal muscle, and motor nerves. Hence it can be seen 

 that the succession of rhythmical excitatory impulses is generally 

 more rapid in proportion as the excitability is greater. This 

 appears not merely from the comparison of the effects of excita- 

 tion in smooth and striated muscles, cardiac muscle and nerve, 

 but also from the phenomena which may be observed at each 

 single excitation of any one of these tissues. If, under the in- 

 fluence of current, or from any other cause, the excitability sinks 



