286 



THE CIRCULATION OF THE BLOOD 



waves) can readily be defined. The receiving button of a second tam- 

 bour, therefore, is applied to the carotid (or radial) artery. 



The writing points of the two tambours (venous and arterial) are then adjusted 

 to the recording surface, their points being so arranged that they lie approximately 

 in the same perpendicular line. Since it is practically impossible to adjust the two 

 styles so that they lie one precisely perpendicular to the other, obviously one style 

 must commence to describe its tracing a fraction of a second before or after the other 

 and vertical lines cutting the two records will not pass through synchronous points. 

 In order to correct for this difference in the time relations of the two curves, each 



'/f SeeonJis I A 3V 



Rex oil <xi 



Fig. 95. Tracings of the jugular pulse, apex beat, carotid and radial pulses. The perpen- 

 dicular lines represent the time of the following events: 1, The beginning of the auricular 

 systole; 2, The beginning of the ventricular systole; 3, The appearance of the pulse in the 

 carotid; 4, The appearance of the pulse in the radial; 5, The closing of the semilunar valves; 6, 

 The opening of the tricuspid valves. (Mackenzie.) 



style (by a gentle tap of the finger while the paper is at a standstill) is made to 

 describe an upright mark. The lines so made are termed alignment marks, and by 

 their means the relative positions of the two writing points are recorded, thus enabling 

 subsequent time measurements to be made with accuracy. After adjusting a time 

 marker (one-fifth second), which should always be employed simultaneously with the 

 pulse tracings, the clockwork mechanism which carries the paper is started and al- 

 lowed to revolve at a moderate speed. (A convenient form of apparatus in clinical work 

 is shown in Fig. 95.) 



The interpretation of the venous pulse tracing is obtained in the fol- 

 lowing way: The distance from the alignment mark of the carotid trac- 

 ing to the commencement of the upstroke of the latter (intersection of 

 line 3) is measured. The same distance is then laid off on the venous 

 tracing, commencing from the alignment mark of this tracing. If a 



