134 
rOPULAR SCIENCE REVIEW. 
Different explanations have been given of the dicrotic rise 
in the sphygmograph trace, and some physiologists still think 
that its true cause has not yet been fully made out. The 
difficulty arises from the fact that at the same time that the 
action of the valves, especially the aortic, have to be con- 
sidered, the many different direct and reflected undulations 
which are possible in distended elastic tubes must not be 
omitted from consideration. All evidence of any significance, 
however, goes to show that this dicrotic rise is simply the wave 
generated by the shock of closure of the aortic valve, trans- 
mitted along the arteries from the large to the smaller vessels, 
just in the same manner as in the primary undulation. 
SPHYGMOGRAPH TRACINGS. 
All taken from the same individual in health, under different conditions, 
to show the effect of difference in pulse-rate on the trace— 
a 44 a m nute 
/3 63 
7 72 
S 103 a minute 
e 137 
C 172 
In the top tracing a is the primary, b the predicrotic, and c the dicrotic rise. 
The small predicrotic irregularity (6) above mentioned in the 
descent following the primary rise, originates from the same 
source as the dicrotic. My observations with an instrument 
which records simultaneously the movements of the heart and 
the pulse at the wrist (the cardio-sphygmograph) prove that it 
is simultaneous with the closure of the aortic valve at the 
heart ; that it is a shock wave in fact, whilst the dicrotic wave 
is the more slowly travelling undulation of distension. 
Now that we know some of the important features of the 
sphygmograph trace, the next point for consideration is how 
