1882.] in the function of the cardiac muscle. 285 



After these preliminary observations we can turn our attention 

 to the strip of muscular tissue cut from the apex of ventricle or 

 auricle as mentioned in Part I. of this paper. In the first place, 

 it is of great interest to observe the way in which the interrupted 

 current brings the muscle into the condition of rhythmical spon- 

 taneity. The result of cutting out the strip is to produce in it a 

 series of blocking points some of which are complete, some partial, 

 so that each contraction-wave at first travels a little way, is then 

 at one place completely blocked, at another delayed in its progress, 

 at another partially blocked, so that every second wave passes and 

 so on; the total result being to produce contractions of irregular 

 form and irregular force. The effect of the weak interrupted 

 current is gradually and slowly to remove these separate blocks, 

 so that the contractions caused by the single induction shocks 

 gradually become stronger, the irregularities disappear and the 

 alternately strong and weak contractions become all strong. 

 Finally, when the blocks have been all removed, when the con- 

 traction-wave travels freely from one end of the strip to the other 

 then the process of repair is complete, then spontaneous contrac- 

 tions appear, and the strip can now be left to itself and will 

 continue beating as long as I have had the patience to watch it. 



We see then that an interrupted current sent through the 

 strip of muscle, which is not strong enough to cause contractions 

 in that strip, repairs the conduction power of the muscular vagus 

 and in this respect therefore acts very similarly to the tissue 

 nerve. 



Again, a weak interrupted current sent through a strip of muscle 

 from the apex of the frog's ventricle or the auricle of the tortoise, 

 when they are made to beat regularly by means of single induction 

 shocks sent in every five seconds, diminishes most markedly the 

 force of these artificial beats during the stimulation and causes an 

 increase after the end of the stimulation exactly similar to what 

 is seen when the vagus is stimulated in the whole heart. 



Further, atropin applied to the muscular strip prevents this 

 action of the interrupted current in exactly the same way as it 

 prevents the vagus action. 



On the other hand, if the interrupted current be sent through 

 the strip from the ventricle of the tortoise, when that tissue has 

 recovered its conduction power, or when it is beating spontaneously, 

 no effect whatever or only the very slightest is produced upon 

 the force of the contractions either during or after the stimula- 

 tion. In this case too then the weak interrupted current closely 

 resembles the action of the vagus. 



It is at present premature to speculate upon the manner in 

 which an interrupted current, not strong enough to cause a con- 

 traction, is able to produce these effects in an isolated strip of 



VOL. IV. pt. v. 21 



