Page 322. 
34 MUTUAL RELATIONS OF THE APEX CARDIOGRAPH 
is calculated from the formula #z = 39 /z. The chief source of error 
in these observations is the slight uncertainty in the rate of movement: 
of the watchwork of the instrument, on which the calculation of the 
rapidity of the pulse depended. a 
On comparing this equation, namely wz = 39,/2, with the one 
above referred to as to the relations of the first cardiac interval, namely, 
ay = 20/z, it is evident that the length of the first cardio-arterial 
interval is ‘5128, or just over half that of the first cardiac interval, 
whatever the rate of the pulse. : 
This being the case, a more precise method is acquired of verifying 
the results arrived at; for by finding the number of times that the first 
cardio-arterial interval is contained inthe first cardiac interval, a 
constant quantity ought to be the result, which is independent of the 
rapidity of the pulse. Table II contains these measurements; and it 
may be seen that, though there is a small range of variation, the num- 
bers are all very near to the theoretical requirement, which is 1:95; 
and their average is 1°983. 
Tas.e II. { 
Sak cesta 2 Number of times 
ii that the first ae that the first 
Rapidity | cardio-arterial | P®PIdity | cardio-arterial 
of interval of interval 
is contained is contained 
pulse. in the first car- pulse. in the first car- 
diac interval. diac interval. 
58 1°95 81°5 1°95 
64 2° 83 2:1 
69 1°9 84 2-1 
70 1°9125 85 1°995 
71 1:975 85°5 1°95 
72 2-058 86 2° 
74, 1°975 88°5 2°05 
76 1°98 91 2°15 
78 1°9 92 1°85 
79 1°925 94, 1°95 
79°5 1°9 97 2°15 
80 1°95 154 1°975 
It is generally known that in the sphygmograph traces of most slow 
pulses there is a notch in the first arterial interval, immediately pre- 
ceding the major fall; and one of the most marked results of the use 
of the cardio-sphygmograph is the determination of the fact that the 
point of closure of the aortic valve at the heart is always exactly 
synchronous with the lowest part of this notch, or the point of abrupt 
change of direction in the major fall of the sphygmograph trace. 
This leads to the almost necessary conclusion that the subsequent 
slight rise cr change in direction of the trace is the result of the simul- 
