THE CIRCULATION OF THE BLOOD 287 



the jugular vein thus obtained, by Bachmann, Fig. 124, is placed in juxta- 

 position for purposes of comparison. 



The first positive wave, a, is caused by the systole of the auricle and 

 amounts to about 9 millimeters of mercury. The first negative wave is due 

 to the relaxation of the auricle. 



The second positive wave, 2 s, is not of auricular origin, but is due to 

 the systole of the ventricle in its early stage corresponding to the period 

 between the closure of the auriculo-ventricular valve, and the opening of 

 the semilunar valves, the period of rising tension, and amounts to about 

 5 mm. of Hg. It is probably due to the bulging of the auriculo-ventricular 

 valve into the auricular cavity, by the still higher ventricular pressure, thus 

 diminishing its size and raising the pressure. 



v 



\J vf 

 af 



FIG. 123. CURVE OF PRESSURE VARIATIONS FIG. 124. CURVE OF PRESSURE VARIATIONS IN 

 IN THE AURICLES. 1 (Enlarged.) (Porter.} THE JUGULAR VEIN. (Enlarged.) (Bachmann.) 



The second negative wave, af y begins with the opening of the semi- 

 lunar valves, determined by comparison with a simultaneously recorded 

 curve of intra-ventricular pressure, and is due in part to the relaxation of 

 the auricular walls, but more especially to a descent of the more central 

 portions of the auriculo-ventricular septum, into the ventricular cavity, 

 due to the contraction of the papillary muscles during the ventricular 

 systole. The hollow cone thus formed enlarges the auricular cavity, 

 withdraws some of its contained blood, and hence lowers the pressure, 

 thus contributing materially to the filling of the auricle. This negative 

 pressure amounts to about 10 mm. of Hg. 



The third positive wave, v, occurs toward the end of the ventricular 

 systole and is probably caused by an inflow of blood from the veins as 

 well as by a return of the auriculo-ventricular septum to its normal position, 

 the result of a relaxation of the papillary muscles at a time when the intra- 

 ventricular pressure is still higher than the intra-auricular pressure. It 

 amounts to about 5 mm. of Hg. 



The third negative wave, vf, appears very shortly after the relaxation of 



* The original tracing obtained by Porter is shown in the ac- 

 companying Fig. 125. The letters designating the waves have 

 the following significance. A, systolic rise; AB, first diastolic 

 fall; BC, first diastolic rise; CD, second diastolic fall; E, second 

 diastolic rise; F, third diastolic fall; G, pause. In Fig. 126 



p CURVE o * ne tracin S nas been enlarged and the waves relettered and named 



PRESSURE 1 VARIATIONS IN in accordance ih the terminology in vogue in the literature of 

 THE AuRiCLE.-(Por/er.) clinical medicine. 



3 The corresponding wave on the curve of the pressure variations in the jugular vein is 

 believed by Mackenzie to be due to the impact of the expanding carotid artery, and hence calls it 

 the carotid, c, wave; inasmuch as it occurs in point of time with the beginning of the ventricu- 

 lar systole, it is also called the systolic, s, wave. 



