I9I4.] MECHANISM OF THE HEART-BEAT. 297 



This very curious phenomenon depends on an obscure mechanism, 

 and unfortunately we have no satisfactory explanation for it. We 

 know that where we have seen it best, it was associated with acci- 

 dental intoxication by the drug digitalis. But we have seen indica- 

 tions of it in other connections which render its interpretation im- 

 possible with our present knowledge. 



Some of the changes which are observed in the ventricular elec- 

 trocardiogram are more easily explained. Considered as a whole, 

 that is to say, in the light of the three usual leads of Einthoven (the 

 first from the two arms, the second from the right arm and the left 

 leg, and the third from the left arm and the left leg), one obtains 

 a great many curves in which the waves in the first lead are inverted, 

 and others in which inversion takes place in the third lead. Changes 

 such as these result from a variety of causes. A heart which is not 

 firmly anchored, but is easily shifted within the chest cavity by 

 changes in the position of the body, may yield curves in which in- 

 verted waves appear. Comparable changes may result when the 

 heart is pushed by air or fluid introduced in the chest, or when it 

 is pulled to one or the other side by bands of adhesion stretched be- 

 tween the heart's surface and the chest wall. The explanation now 

 ofifered for these phenomena by Einthoven and others is that the 

 relation, determined by Waller, of the electrical axis of the organ to 

 the body axis has become altered. Similar causes are probably at 

 work in the electrical changes which are seen in increases in size of 

 the heart, whether due to dilatation of its cavities, or to thickening 

 of its walls ; and the curves vary according to which side of the organ 

 is involved. When the right side undergoes these changes, it is in 

 the first lead that the ventricular waves become negative (Fig. 4) ; 

 when it is the left side (Fig. 5), the negative waves appear in the 

 third lead. Although alteration in the relation of the electrical axis 

 and the body axis is the cause, that is to say, the mechanical, ana- 

 tomical cause, commonly given for such deviations from the normal 

 curve, it appears necessary to remember that in hypertrophy of the 

 heart the balance of the sum of potential dififerences which produces 

 the normal electrocardiogram must be disturbed, and that a rear- 

 rangement, that is to say, a functional rearrangement, of the parts 

 of this sum must occur and might of course result in the changes we 



