ELECTROCARDIOGRA M 



19 



further progress the advancing border of the wave is not only proceed- 

 ing toward the apex, but is now also traveling back in the lateral walls 

 to reach the base (Fig. 6B end-phase left-hand figure). Activity in 

 the region of the apex still tends to maintain the electric axis 

 from base to apex ; the basal activity tends to set it in a contrary direc- 

 tion. But the effect of this basal activity is apparently insufficient 

 to upset the average direction, which still remains from base to apex. 

 The basal contact is throughout relatively negative to the apical contact. 

 If, however, as often happens in the amphibian heart, the basal seg- 

 ments of muscle are the last supplied, this opposition of the apical 

 effects is removed and the effect of basal activity then appears It 

 manifests itself in the form of an 6" wave, a downward deflection 

 indicating relative negativity of the apical contact. The axis of the 

 electromotive force is now from below upward (Fig. 6B end phase, 

 right-hand figure). 



03-5- 



ow 



OZ.5" 



ozso 



Fig. 8. Tim'es of arrival of excitation wave relative to each other indicated 

 in decimal points of a second. 



Thus, our hypothesis brings us to a reasonable explanation of a 

 curious but actual observation, namely, that the appearance of an 5 

 wave in the electrocardiogram of amphibians is associated with late 

 arrival of the excitation wave at the ventricular base. No other present 

 day hypothesis will afford an explanation of this phenomenon. This 

 example is in my view precisely comparable to that of the bulbus 

 already cited. In both instances basal activities are responsible for 

 relative negativity of the apical contact ; but the present illustration has 

 an advantage over the first, in that there can be no question here of 

 separate muscle systems ; the whole of the musculature of the ventricle 

 is one uniform syncytium. 



THE MAMMALIAN ELECTROCARDIOGRAM 



Similar methods of observation are applied to the mammalian ven- 

 tricle and, although in this instance we deal with a far more complex 

 arrangement, similar correlations can be shown to exist between the 

 manner in which the excitation wave spreads and the set of the elec- 



