Ill 



ELECTRICAL EXCITATION OF MUSCLE 



197 



to assume that a sustained and persistently flowing current in m//// 

 cases, perhaps always, sets up a discontinuous state of excitation, which 

 only produces an (/p/>t</-<'//f/// steady contraction, because the conditions 

 of experiment are usually such that weak rhythmical contractions 

 that arc feeble in character or confined to single bundles of fibres, 

 remain without visible, mechanical expression. From this point of 

 view it would be legitimate to speak of tetanic closure twitches, 

 and of a tetanic character of the persistent closure contraction ; 

 indeed it seems doubtful whether on exciting a curarised muscle 

 with strong battery currents a simple non-tetanic closure twitch 



vAA/\ 



FIG. S3. Rhythmical series of twitches from sartorius ; persistent closure of current ; gradual 



increment of twitches. 



really can be obtained the extended curve rather speaks in 

 favour of this view than against it. How far it is really legiti- 

 mate to draw inferences from this to the mode of action of weaker 

 currents must provisionally be left undecided, just as it is not 

 possible from our present experimental data to postulate the dis- 

 continuous nature of the persistent closure contraction, although 

 there is much to be said for it. The constant current, during 

 its closure in cardiac muscle, thus produces a regular and invari- 

 able series of rhythmical contractions, which also appear, at least 

 under certain conditions, in striated skeletal muscle ; and this is 

 still more the case in smooth muscle. Engelmann (5) was the 

 first to observe an appearance in the ureter of the rabbit, which 

 may be regarded as the undoubted analogue of the facts under 



