Page 446. 
42 ON PULSE FREQUENCY, 
8. ON PULSE FREQUENCY, AND THE FORCES 
WHICH VARY IT.* 
THE circulation of the blood is a uniform circulation, the pulsation 
being neglected, and a uniform circulation is one in which the quantity 
of fluid flowing through all segments of the circulating system is the 
same; otherwise there would be a tendency for the fluid to accumulate 
at certain points, which is contrary to the premises. 
To arrive at precise conclusions respecting the circulation there 
are two points which must be considered :—1st., The laws which regu- 
late the flow of fluids through capillary tubes. 2nd., The variations 
in the capacity of the circulating system under different pressures. 
These will be considered separately. Poiseuille found that the flow of 
fluids through capillary tubes varies directly as the pressure and as 
the fourth power of the diameter of the tubes. The author has 
verified the former of these results on the vessels of the animal system 
by a different method. Respecting the capacity of the arteries and 
ventricles under different blood-pressures, it is evident that the 
capacity of the former must depend on the pressure only, for they are 
simple elastic tubes, and must be more capacious under high than 
under low pressures; reasons are given below for a more precise state- 
ment of this relation. To maintain a uniform circulation with a 
pulsating motor, like the heart, it is evident from the above considera- 
tions that variations in the resistance at the small arteries must pro- 
duce variations in pulse-rate; and that unless the capacity of the 
arteries and heart vary directly as the pressure, variations in blood 
pressure must be also attended with change in pulse frequency. That 
the capacity of the ventricles is dependent on the arterial blood pres- 
sure can be proved by the varied amount of opening up of the 
ventricular cavities which follows different fluid pressures in the 
coronary arteries. 
Next, the different forces which vary the pulse-rate must be con- 
sidered. It can be shown that any change in the resistance to the flow 
of blood through the capillaries varies the pulse-rate, increased re- 
sistance rendering the pulse slower, and the reverse. As instances of 
these effects may be given, the pulse-slowing effects of stripping in a 
cold air, of a cold bath, and of compression of large arteries; the 
* “ Nature,” VI. pp. 446, 7. Sept. 26, 1872. Paper read before the British 
Association at the Brighton Meeting in Section D, Department of Anatomy and 
Physiology. See “ Report of British Association,” 1872, p. 151. 
