70 THE HEART 



there is ho very positive evidence of this point, although the 

 tracings of the cardio-pneumatic movements appear to indicate 

 its presence. 



From anatomical considerations, therefore, we come to the con- 

 clusion that the excitatory wave in its passage through the heart 

 travels from the parts representing the venous end of the primitive 

 cardiac tube to those developed from the arterial end. If this be 

 the case, evidence of this passage should be forthcoming from the 

 records obtained by different observers in regard to the electro- 

 motive phenomenon of the beating heart.' Considerable discrepancy, 

 however, appears in such records. Waller and Reid found in 

 several mammalian hearts that the excitatory wave normally 

 passed from apex to base. Bayliss and Starling, on the other 

 hand, observed the wave to pass normally from base to apex, 

 and only in the injured heart to pass in the reverse direction. 

 Schliiter's experiments on the cat's heart appear to support Waller 

 and Reid. 



In view of this divergence of opinion the recent valuable 

 work of Gotch upon the frog's heart is of great interest. His 

 records distinctly show that it quite depends upon which part 

 of the base of the heart the electrodes are placed as to what 

 form of curve is obtained. Normally, however, he is convinced 

 that the excitatory wave passes from the venous base of the 

 ventricle to the apex and thence to the aortic base in connection 

 with the great arterial trunks. Gotch's results also show that a 

 high intracardiac pressure brings into prominence the action of 

 that part of the ventricle leading up to the aorta. This is there- 

 fore important confirmatory evidence of Keith's view of the action 

 of the different sets of muscles in the ventricle; 



When, too, we realise how small an area the A-V bundle in 

 the mammalian offers to the electrode, it is easy to understand 

 that contradictory results should be obtained for the mammalian 

 heart. There is every reason to suppose, therefore, that in the 

 mammalian heart also the excitatory wave follows the direction 

 of the primitive cardiac tube, and passes from the venous base 

 to the apex, and thence back to the aortic base, ensuring thereby 

 an orderly sequence of movements. More work is wanted to 

 elucidate these movements and also many other points, the im- 

 portance of which lies in the fact that " the heart . . . is the 

 beginning of life ; the sun of the microcosm ; ... it is the house- 



