THE HEART-BEAT IN ITS PHYSIOLOGICAL RELATIONS 149 



the auriculo-ventricular band, since this band is richly provided 

 with nerve- fibres as well as ganglion-cells (Wilson). Yet it is 

 unlikely that all the nerves capable of conducting the impulses to 

 contraction should be gathered into such a narrow compass, and 

 therefore the experiment supports the view that the conduction is 



Pig 65 Jugular (Upper) and Carotid (Lower) Pulse-Tracing from a Case of Arterio- 

 sclerosis, showing Partial Failure of Conduction in the Auriculo-Ventricular 

 Bundle (Cushny and Grosh). The ventricle only beats once to two beats of the 

 auricle. Time-trace, fifths of a second. 



carried out in the muscular tissue. And if the conduction of the 

 excitation from auricles to ventricles is accomplished by a muscular 

 connection, it' is natural to suppose that .the co-ordination of sym- 

 metrical portions of the heart on either side of the longitudinal axis, 



Fjg 66. Tracing of Jugular (Upper) and Radial (Lower) Pulse from a Man with 

 Heart-Block (Lewis and Macnalty). In the cycles marked 34. 35. and 36 the 

 ventricular contraction, although less frequent than the auricular, was initiated 

 from the auricle. In the last two cycles (37 and 38) and the pause of 36 complete 

 heart-block was present. On the jugular trace the a~c interval (representing 

 the interval between the onset of the auricular and ventricular contractions) is 

 given, and on the radial trace the duration of a cardiac cycle, both in fifths of a 

 second. 



the co-ordination in virtue of which the two auricles contract 

 together and the two ventricles together, is also achieved by the 

 passage of impulses through the muscular tissue. In accordance 

 with this, it has been shown that the ventricles in the dog and cat 

 continue to beat in unison, after the attempt has been made to 



