1882.] in the f miction of the cardiac muscle. 283 



Besides these three sets of effects I came to the conclusion 

 that a fourth must be added ; viz. diminution and increase of 

 excitability ; since then, however, my experiments on the tortoise 

 heart 1 have shown me that the observations upon which 1 relied 

 for the proof of the influence of the vagus on the muscular ex- 

 citability were in reality proofs of the action of the nerve upon 

 the power of the muscular tissue to conduct a wave of contraction 

 along it. This is clearly shown by the resemblance between 

 the results of these experiments on the frog and those described 

 in the two subsequent papers quoted above, which demonstrate 

 conclusively the power possessed by the vagus of removing and 

 increasing a block of the contraction-wave caused artificially by 

 the section of the auricle of the tortoise. We may therefore add 

 to the above mentioned effects of vagus action 



4. Diminution and increase of conduction power. 



Further, in close connection with this last action is the influence 

 of the vagus on the sequence of the contractions ; thus, as is 

 pointed out in my paper read before the British Medical Association, 

 the natural slight blocking of the contraction- wave at the junctions 

 of the sinus and auricles and of auricles and ventricle respectively, 

 may be converted by the vagus into a complete block, so that the 

 contraction-wave may never reach the auricle in the one case or 

 the ventricle in the other. On the other hand when the natural 

 block at these two junctions is by any means intensified so that 

 only every second contraction-wave passes, then the vagus may 

 remove that block and cause every contraction to pass. 



Again the length of the pause between the contractions of 

 the sinus and the auricle may be increased or diminished by the 

 action of the vagus ; this is especially well seen in the snake 

 when as is apt to occur a very measurable pause ensues between 

 the contractions of the sinus and auricles. We may therefore add 

 as corollaries to (4) 



5. Cessation and recovery of sequence, 



6. Diminution and increase in rapidity of sequence. 



All these different effects may on the view put forth in Part I. 

 of this paper be summed up by saying, 



The vagus possesses the power of depressing and exalting all 

 the different functions of all the different muscular tissues of the 

 heart. 



In addition, it is to be noticed that although the initial effect 

 of the vagus is often to depress some function, its final and most 

 enduring power is to exalt, intensify and repair that function. 

 Thus, although it slows rhythm, yet its stimulation makes the 

 rhythmical power last longer than it otherwise would, and makes 



1 Op. eit. 



