258 PHYSIOLOGY OF THE HEART [CH. XXL 



do begin to beat again, the ventricular beat is much less frequent 

 than the auricular, and bears no relationship to it. This lack of 

 correspondence in auricular and ventricular rhythm is known as 

 arhythmia. 



When the bundle is destroyed by disease in man (Stokes- Adams' 

 disease) there is a similar dissociation between the auricular and 

 ventricular rhythm, the ventricles beating slowly and the auricles 

 rapidly. Sometimes the "heart-block" is incomplete. This is seen 

 in the early stages of the disease ; then one out of every two or 

 three auricular waves gets over to the ventricle, just as in Gaskell's 

 experiments on the frog's heart when the clamp is not sufficiently tight. 



These recently discovered facts throw a good deal of light on 

 the propagation of the normal heart wave. It starts in the sino- 

 auricular node, and spreads thence to both auricles ; it also travels 

 to the ventricles by the auriculo- ventricular bundle, reaching first 

 the papillary muscles, and thence the rest of the heart until it 

 arrives at the apex, and finally returns by the spiral fibres (see 

 p. 212) to the base of the heart in the region of the origin of the 

 pulmonary artery, which is the representative of the bulbus aortse of 

 the primitive heart. It is therefore not surprising that the electro 

 cardiogram (p. 246) is complex. The wave P due to auricular 

 activity is followed by a pause before the waves which accompany 

 ventricular systole occur. During this pause it is supposed that 

 the excitatory wave is travelling along the auriculo -ventricular 

 bundle, the mass of which is too small to affect the galvanometer. 

 The pause which intervenes after the wave E, which is the sign of 

 commencing ventricular activity, is supposed to be due to a state of 

 equipotentiality when the great mass of the circular muscles of the 

 ventricle are contracting; the final wave T indicates the arrival of 

 the contraction wave at the base by the spiral fibres. 



The Stannius Experiment. This consists in applying a tight ligature 

 to the heart between the sinus and the right auricle ; the sinus 

 continues to beat, but the rest of the heart is quiescent. The quiescent 

 parts of the heart may be made to contract in response to mechanical 

 or electrical stimulation. If a second ligature is applied to the 

 junction of the auricles with the ventricle, the ventricle begins to 

 beat again; the auricles may also beat, but they usually do not. 

 According to Gaskell, the effect of the first ligature is simply an 

 example of blocking ; it is, however, difficult to wholly accept this 

 view, for if instead of applying a ligature at the sino-auricular 

 junction, the heart wall is simply cut through at this spot, the 

 auricles and ventricle are not thereby always rendered quiescent. It 

 appears probable, therefore, that there is some truth in the older 

 view that the ligature acts as a stimulus irritating the vagal termi- 

 nations in Eemak's ganglion, and so eliciting a condition of prolonged 



