THE FREQUENCY OF THE PULSE. 57 
that is, the period during which the heart is being opened out by the 
regurgitation of blood from the arteries. 
The length of the combined systole and diaspasis not depending at 
all on the pressure, and it being constant for any pulse-rate, it is 
infinitely probable that the systole and diaspasis separately are inde- 
pendent of the pressure, and this is extremely interesting, as it gives 
a further insight into the mechanism of the heart. For, in order that 
the duration of the diaspasis should not vary with different blood 
pressures, it is evident that with higher pressures there must be 
greater obstruction to the heartward flow of blood, otherwise the 
valyes would then close more quickly. And this is exactly what 
would be expected from the combination of Mr. Bryan’s observations 
concerning the shape of the heart, and Briicke’s theory of the active 
diastole of the ventricles.* According to the latter author the cardiac Page 21. 
"muscular tissue has no inherent power of opening out the ventricles, 
but remains inactive after systole, during diaspasis in fact, until the 
regurgitation from the aorta has closed the aortic valves and so un- 
covered the orifices of the coronary arteries, immediately upon which 
the resulting sudden turgescence of the heart’s walls makes them open 
up. Mr. Bryan has shown that during systole the whole heart alters 
its position as a result of its change in shape during contraction, and 
recovers it during diastole; therefore the greater the force of contrac- 
tion the more will it alter its shape, and the more difficult will it be 
for it to resume the original one, which has to be done partly by the 
regurgitating arterial blood; but the greater the blood pressure, the 
greater will be the facility for overcoming this greater work, which 
two, as must be the case, vary together. This argument explains how 
the diaspasis need not vary in length with different blood pressures. 
Next, with regard to the systole. As the first part of the heart’s 
beat varies as the square root of the length of the beat, and as the 
diaspasis, a part of that first part, does not vary with the blood pres- 
sure, upon which alone it can depend, it is necessary that the other 
component of that interval must vary more than as the square root of 
the pulse length. And to find how much more quickly, it is necessary 
to obtain the actual length of diaspasis. Careful measurements of a 
cardiograph trace, beating 102 in a minute, give the ratio of the 
systole to the whole beat as 1 to 3°1915, and that of the first part to Page 22. 
the whole beat as 1 to 20, which leaves the ratio of the diaspasis to 
the beat as -187 to 1, or the diaspasis length as 00183 of a minute. 
A similar length of diaspasis is found from quicker pulses. 
% * Mr. Bryan’s paper is in the “‘ Lancet,” Feb. 8th, 1834. 
- Briicke’s theory appeared in “Sitzungsberichte der Wiener Akad. der Wiss.,” 
1854, Vol. XIV. p. 345. A paper on the same subject by myself will be found in 
_ the “ Journal of Anatomy and Physiology,” May, 1869. (Supra, p. 3.) 
