290 THE CIRCULATION OF THE BLOOD 



lowing features. A short distance (about one-tenth second) in front of 

 the upstroke of the cardiogram a small wave, sometimes, appears. This 

 is due to auricular systole and is termed the auricular (a) wave of the 

 apex curve: its commencement coincides with line 1. The main steep 

 rise in the curve is due to ventricular systole. Its commencement, which 

 coincides with the closure of the auriculo-ventrieular valves, is inter- 

 sected by line 2. Turning now to the carotid tracing it is found that 

 a measurement made from its alignment mark to the commencement of its 

 upstroke when transferred to the apex tracing in the usual way falls 

 near the upper part of the upstroke of the latter tracing. This point 

 marks the opening of the semilunar valves and is intersected by line 3. 

 Measuring again on the carotid tracing from its alignment mark to the 



Fig. 98. Polysphygmograms including jugular, apex and radial tracings. Line 4 on the radial 

 tracing is first of all located. It is then transferred (by measurement from the alignment mark on 

 the right edge of the tracing) to the jugular and 1/10 second subtracted from it, giving line 3. 

 When this is similarly transferred to the apex tracing, it falls somewhere on the upstroke the be- 

 ginning of which is line 2. 



beginning of the dicrotic wave and applying this measurement to the 

 apex tracing a point is defined near the beginning of the downstroke 

 of the latter. This marks the time of closure of the semilunar valves 

 and is intersected by line 5. The termination of the downstroke in the 

 apex curve in the same way may be shown to be synchronous with the 

 termination of the dicrotic wave in the carotid tracing. This point in 

 the cardiogram, which is crossed by line 6, marks the time of opening of 

 the auriculo-ventrieular valves. 



The intervals between the lines 2 and 3, 3 and 5, and 5 and 6 are 

 termed the presphygmic (space D), sphygmic (space E), and post- 

 sphygmic (space F) periods respectively (see page 150). The period 



