90 CIRCULATION OF THE BLOOD. 
the same in arteries at different distances from the heart, the radial 
sphygmograph-trace expresses their duration in the aorta. : 
II. The cardiosystole being longer than the sphygmosystole at all 
possible pulse-rates, the excess in the length of the former expresses 
the time required by the heart to reach, from a state of rest, a systolic 
pressure sufficient to open the semilunar valves. This interval, termed 
the syspasis, is constant for any given rapidity of cardiac action, and 
rapidly decreases as the pulse gets quicker, becoming nil at a rate of 
170 a minute. 
III. The interval between the commencement of the primary pulse- 
rise in the radial and that in the posterior tibial artery is less than 
would be estimated from the time taken by the same wave in travelling 
from the aortic valve to the radial artery. 
The woodcut (p. 89) will assist in illustrating the mutual rela- 
tions of the different component parts of the cardiac revolution, as its 
different elements are there shown in their actual relations one to the 
other. 
