Upon the Motion of the Mammalian Heart. 567 



which encircle both cavities, while others limit themselves to a single 

 cavity. The chief spiral bands start at the bases of the ventricles and pass 

 to the apices of the ventricles where, turning sharply, they form vortices 

 and pass up to constitute the papillary muscles. The arrangement is such 

 that these layers may be dissected off one by one, and as each new layer is 

 reached, the inclination of the fibres alters. 



Our first efforts (17) to unravel the course of the excitation wave took 

 account of these muscle bands, for we naturally supposed the course of the 

 wave to be controlled by them. But the readings which we obtained 

 demonstrated to us clearly that the times at which the excitation wave 

 appears at different points of given superficial bands are incompatible with 

 this view. "We explored the whole superficies of the ventricle, and 

 constructed maps of the ventricle in a number of animals which showed the 

 precise surface distribution of the excitation wave in relation to time. 

 These maps portrayed a number of new facts. It was to be seen that the 

 system of distribution is tolerably uniform from animal to animal ; it was 

 shown, considering each ventricle separately or the two. ventricles together, 

 that points widely apart are activated simultaneously. A simple form of 

 distribution, the passage of the wave from one muscular element to the 

 next, a radial spread from a given point on each ventricle or a given area of 

 each ventricle would not suffice ; we were compelled to recognise that the 

 spread occurs to a large number of surface points simultaneously ; no other 

 hypothesis could explain the rapidity of the spread or the order of it ; we 

 were forced to the conclusion that the excitation wave is distributed by a 

 number of separate and distinct channels. This conclusion was at variance 

 with the conclusions of workers who had previously used the electrical 

 method : these had all assumed a simple form of spread ; but it harmonised 

 in a general way with the recent anatomical discovery of the arborisations of 

 the A- V bundle. Attention was consequently directed to this system, and 

 experiments specially devised to test the matter proved its importance. 



If after mapping out the distribution of the wave to the ventral surface of 

 the two ventricles, the right division of the auriculo-ventricular bundle, 

 which breaks up into the network of the right ventricle, is divided, the 

 spread becomes altered (17 and 18). Over the left ventricle it remains 

 unchanged, over the right ventricle it is delayed ; moreover, after such a 

 lesion, the order in which the surface is activated is found changed ; the 

 wave now starts at the margin of the right ventricle where it borders the 

 left ventricle and travels over the ventricle away from this margin. Briefly, 

 when the right division of the bundle is cut, the excitation wave at first 

 spreads only to the left ventricle ; later, when the left ventricle is 



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