THE EVENTS OF THE HUMAN CARDIAC CYCLE 83 



careful investigation at the hands of Chauveau and Marey, D'Es- 

 pine, 1 Fredericq ( m ), Frey and Krehl ( 13 ), and Porter. Recently 

 Hering ( 23 *) has studied the same subject, using the perfused heart ; 

 and further observations have been made by Rautenberg (*' c ). 

 For the most part the experiments have been on dogs ; those of 

 Chauveau and Marey were carried out on the horse. 



The curves given by Porter are perhaps as much in accord 

 with the general evidence as any, and it will be found convenient 

 to take these as typifying the changes in intra -auricular pressure, 

 eventually examining the results of experimental work in relation 

 to such a type. In common with all other observers Porter found 

 that auricular contraction is accompanied by a positive wave 

 of pressure. At or a little before the termination of auricular 

 systole this " first positive wave " 2 gives place to a " first negative 

 wave," a wave which, but for the interposition of the "second 

 positive wave," forms with the " second negative wave " the main 

 depression of auricular pressure during the cycle. (A curve illustrat- 

 ing the waves and their relation to the curve of intra-ventricular 

 pressure is given in the accompanying figure, Fig. 1). The second 

 positive wave, which breaks this otherwise steady fall, is said by 

 most writers on the subject to occur at the onset of ventricular 

 systole, and is usually figured as lasting until the point which marks 

 the opening of the semilunar valves. 3 The wave is well shown on 

 the tracings of Chauveau and Marey, D'Espine, Fredericq, Porter, 

 and Rautenberg, but it is absent from those of Frey and Krehl. 

 Porter (p. 526) noted its absence on occasion. Fuller details of 

 its significance will be discussed later. Relaxation of the auricular 

 wall is stated by Porter to last to the beginning or end of this 

 wave. The point at which the second negative and " third posi- 

 tive waves " meet is at present the subject of considerable dis- 

 cussion. Chauveau and Marey placed it at the end of ventricular 

 systole, 4 but otherwise there appears a consensus of opinion, 



1 Cited by Fredericq ( ia , p. 524 and Fig. 19). 



* In the auricular tracings given by Porter there are in all three main elevations 

 and tlncf main depressions. The terminology of the curves is at present so con- 

 fused that the employment of Porter's original designations is ini{ossible. In the 

 following pages the rises and falls will be s]>okeii of as the first, second, and third 

 jH.sitivc, ami the first, second, and third negative, wave respectively. 



1 A point estimated by means of differential manometer tracings (Hurthle 

 ami "there). 



* In the tracing given in the On:, me//. <t. J'ttris, 1861, p. 673, the second positive 

 wave is not shown, and the third positive wave commences during the systolic 



