Page 19. 
Page 20. 
56 THE LAW WHICH REGULATES 
published in the 5th vol.of the “ Journal of Anatomy and Physiology,’’* 
I have endeavoured to substantiate a law respecting the elements of 
the heart’s beat, which may be thus enunciated :— 
The heart’s beat consists of two parts, which for any given pulse- 
rate do not vary in their ratio to one another; but the length of the 
first part varies inversely as the square root of the sap of the 
pulse. 
A second series of measurements of the cardio-arterial intervals, 
published in the ‘‘ Proceedings of the Royal Society,”’t have further 
verified the law just stated, and in the rest of this paper it will be 
assumed as proved. No theory respecting the circulation throws light 
on its significance; but the one which it has been my endeavour to 
demonstrate above gives a very satisfactory explanation of it, which 
will now be considered in detail. 
First, the heart’s beat consists of two parts, which for any given 
pulse-rate do not vary in their ratio to one another. It having been 
proved previously that the pulse-rate does not depend on the blood 
pressure, and, as shown now, the length of the first part of the heart’s 
beat not varying when the pulse length is constant, it is evident that 
the length of the first part of the pulse-beat does not depend on the - 
blood pressure in any way. 
- Again, the first part of the pulse-beat is compound, for it is thee 
interval between the commencement of the cardiac or ventricular 
systole and the closure of the semilunar valves; therefore it may be 
divided into the systole and the valve-closure interval. 
Physiologists have laid very little stress on this valve-closure 
interval, it generally being considered as instantaneous. But in the 
study of cardiograph tracings it is to be remembered that the dis- 
tances between events occurring within one-fiftieth of a second of one 
another can be appreciated withont much difficulty, and there is every 
a priort reason for believing that this interval has a longer duration 
than that. In my paper on the cardiograph trace, reasons have been 
given for the belief that in quick pulses the commencement and the 
end of this valve-closure interval are indicated by separate and distinct 
changes of direction in the curve, and its length as obtained by 
measuring from these points agrees entirely with that required from 
arguments to be mentioned further on. It may be called the diaspasis, 
rise for the auricular, and was so led to the conclusion that the length of the cardiac 
intervals depended in some measure on the position of the body. This is incorrect, 
as subsequent measurements show me, and the length of the first part does not vary 
with the position of the body ; the proper equation for finding the cardiac first part 
under all circumstances being zy = 20 V2. 
* Supra, p. 18. 
+ Supra, p. 32. 
