THE CIRCULATION OF THE BLOOD AND LYMPH 91 



first elevation corresponds to the systole of the auricle. The 

 second coincides with the onset of the ventricular systole, and 

 is, perhaps, due to the sudden bulging of the auriculo-ventricular 

 valve into the auricle, or even to a slight regurgitation of blood 

 from the ventricle through the valve before it has completely 

 closed. The cause of the third elevation, which occurs during 

 the period occupied in the ventricular pressure-curve by the 

 plateau, is less clearly made out. In man, the events taking place 

 in the right auricle during its systole can be followed to some 

 extent by recording the venous pulse in the jugular veins, 

 especially the internal jugular, at the root of the neck (Fig. 30). 

 Successful tracings can be obtained, not only in certain pathological 

 conditions, but in many normal individuals, and it is probably 



FIG. 30. SIMULTANEOUS RECORD OF JUGULAR PULSE, VENTRICULAR CONTRAC- 

 TION, AURICULAR CONTRACTION, AND CAROTID PULSE IN DOG (CUSHNV AND 

 GROSH). 



a, c, v, the three elevations of the jugular pulse. Time-trace, fifths of a second. 



only a matter of improved technique to obtain them in all. The 

 jugular venous pulse-tracing, like the intra-auricular pressure- 

 curve, shows in general three well-marked elevations and three 

 depressions, and there is good evidence that, broadly speaking, 

 these features of the jugular curve correspond as regards their 

 origin with the changes of pressure in the auricle. Some differ- 

 ence of opinion exists as to how the changes of pressure in the 

 auricle are propagated into the veins, although there seems to 

 be little reason to suppose that in normal persons any actual 

 regurgitation of blood takes place. It is also a debatable ques- 

 tion how far pulsation transmitted from the great arteries of the 

 thorax and neck may affect the jugular tracing. But be this as 

 it may, the jugular curve, when properly interpreted, affords 

 valuable information as to the action of the auricle, information 

 of the same kind as that afforded by the arterial pulse-tracing 

 and the cardiogram as to the action of the ventricle. The 



