THE CIRCULATION OF THE BLOOD AND LYMPH 137 



pendently of the auricle, the stimulus to contraction originating, 

 perhaps, in the uninjured portion of the bundle below the seat of 

 the block. These conditions are most easily recognised by comparing 

 tracings simultaneously obtained from the jugular vein and the 

 radial artery or apex-beat (p. 82). When the block is complete 

 the rate of the ventricle is very slow (about 30 in the minute, or less), 



FIG. 55. JUGULAR (UPPER) AND CAROTID (LOWER) PULSE TRACING FROM A 

 CASE OF ARTERIO-SCLEROSIS, SHOWING PARTIAL FAILURE OF CONDUCTION 

 IN THE AURICULO-VENTRICULAR BUNDLE (CUSHNY AND GROSH). 



The ventricle only beats once to two beats of the auricle. Time-trace, fifths 

 of a second. 



the time of the ventricular beat is clearly unrelated to that of the 

 auricular, and the stability of the ventricular rhythm is abnormally 

 great, such circumstances as usually cause a marked increase in the 

 pulse-rate mental excitement, for instance affecting it little or 

 not at all. This is the condition in the so-called Stokes- Adams 



FIG. 56. TRACING OF JUGULAR (UPPER) AND RADIAL (LOWER) PULSE FROM A 

 MAN WITH HEART-BLOCK (LEWIS AND MACNALTV). 



In the cycles marked 34, 35, and 36 the ventricular contraction, although less 

 frequent than the auricular, was initiated from the auricle. In the last two 

 cycles (37 and 38) and the pause of 36 complete heart-block was present. On the 

 jugular trace the a-c interval (representing the interval between the onset of the 

 auricular and ventricular contractions) is given, and on the radial trace the 

 duration of a cardiac cycle, both in fifths of a second. 



disease. In some of these cases pathological (syphilitic) changes in 

 the atrio- ventricular bundle have actually been discovered at autopsy. 

 In others there is some reason to believe that abnormal excitation 

 of the cardio-inhibitory nerves may be responsible even for long- 

 continued block, especially when the conductivity of the bundle 

 has been already permanently diminished. 



