292 COHN— STUDY OF THE [April 23. 



by the ventricular base, while vS indicates a return of activity to the 

 apex. The significance of the T wave is a hotly disputed point. 

 Some hold it to represent the return of activity to the base of the 

 ventricles in the later part of systole, because of an analogy which is 

 drawn between the arterial base of the heart and the distal end of 

 the primitive cardiac tube, which is, of course, the last segment to 

 become affected by the wave of peristalsis which passes over it. 

 The most important arguments against this interesting assumption 

 have been supplied by Garten and his pupils, Clement and Erfmann. 

 These investigators have all shown that the T wave occurs at the 

 same instant of time at all points on the heart's surface, and refer 

 its occurrence, as does also Einthoven, to a function inherent in 

 muscular contraction. According to these authors, it represents the 

 second wave in a current essentially diphasic. One need scarcely 

 point out the fact that its presence simultaneously throughout the 

 cardiac surface precludes the possibility of its occurring as the end 

 phase of a peristaltic contraction. 



Aside from the auricular representative and the group of waves 

 representing ventricular activity, two other portions of an electro- 

 cardiographic curve must be described. The less debated of these 

 is the portion following the T wave, the isoelectric period between 

 the end of T and the beginning of P. It represents the diastole of 

 the heart cycle, — from the end of the ventricular to the beginning of 

 the next auricular contraction, — the rest period of the heart. The 

 other portion is that lying between the wave P and the complex 

 QRST; this portion also is usually isoelectric, but occasionally, as 

 Einthoven has pointed out, its level departs from the base line. It is 

 the period which represents the time occupied by the passage of im- 

 pulses from the contracting auricles to the beginning of ventricular 

 activity, and is called the conducting period. 



We must now return to consider those other newer aspects of the 

 study of the mechanism of the heart-beat to which I have referred 

 in speaking of recent anatomical and physiological contributions. 

 Before 1883 the theories held to explain coordination between the 

 upper or auricular pair of the cardiac chambers and the lower ven- 

 tricular pair consisted principally of an old notion of Haller's to the 

 effect that the ventricles contracted in response to stimuli conveyed 



