THE EVENTS OF THE HUMAN CARDIAC CYCLE 93 



before pronouncing a definite opinion as to the time relations 

 of the auricular contraction as represented in o?sophageal 

 curves ; and this the more as the example given is one of the 

 most simple. 



It is requisite that the delay in onset of the " a " wave in the 

 neck should be definitely ascertained, but at present the data are 

 insufficient. 1 



(Esophageal curves show the second positive wave with great 

 constancy (Fredericq, Joachim, Minkowski, Rautenberg, and 

 Young and Hewlett), and its onset is said to .coincide with 

 ventricular systole. Young and Hewlett, and Rautenberg agree 

 in showing that it occurs on these curves earlier than the " c " 

 wave upon the jugular tracings. According to the former, the 

 delay 2 is *1 sec. ; according to the last named, '079 sec. 3 (average 

 of six observations). The necessity of fixing the time difference be- 

 tween the second positive and the " c " wave will be obvious when 

 the following facts are taken into consideration. As we have seen 

 the a-c interval is of great clinical importance, and is usually of 

 2 sec. duration as recorded with the polygraph from the jugular 

 vein in the neck. Such evidence as we possess tends to show that 

 the time difference between the onset of auricular and ventricular 

 contraction, as registered by cesophageal and direct auricular curves 

 in man and animals, is less, and amounts to little more than - 1 

 sec. 4 The difference in the two figures can only be accounted for, 

 assuming them to be correct, by the quicker appearance of the 

 " a " wave in the neck. 



In cesophageal tracings a third positive wave is present. Here, 

 as in the case of the " v " wave, opinion is divided as to its moment 

 of onset. Minkowski finds that it commences with the second 

 sound ; Young and Hewlett represent it as commencing in the 

 middle of the ventricular plateau, and ending at or a little before 



1 The electrocardiogram taken simultaneously with the jugular curve should give 

 a speedy answer to this question. A few such curves obtained by the author show 

 a delay of approximately '08 sec. (For .which see appended note and Fig. 3.) 



1 It is necessary to antiei}>ate the discussion of the identity of the two waves. 

 The full evidence will be considered later. 



1 The figures are in agreement with other values, for allowing *05 sec. for the 

 presphygmic interval and '03 sec. for transmission from aorta to carotid or sub- 

 clavian, we obtain a delay in the arterial shock of '08 sec 



4 Einthoven's electrocardiograms show an interval varying from -1 to '2 sec. 

 between onset of auricular and ventricular potential change. The average is about 

 '14 sec. in man. 



