LAW REGULATING THE FREQUENCY OF THE PULSE. 45 
9. ON THE LAW WHICH REGULATES THE FRE- 
QUENCY OF THE PULSE.* 
| THE paucity of mechanical theories to explain the frequency of the 
pulse, probably arises from the very general assumption, that in all 
cases when the rapidity of the heart’s beat is caused to vary, the 
Page 1, 
action of nerves with special powers of retarding or quickening it is ~ 
brought into play ; and the relation of heart power to work to be per- 
formed, has not been introduced into the problem. 
The theory of energy has of late spread so far and wide the neces- 
sity for finding in all cases where work is done a sufficient source for 
the production of that work, in one form or other, that a vague state- 
ment to the effect that heart frequency depends solely on nerve action, 
is far from sufficient for the requirements of physiologists. It is now 
necessary to show that with different amounts of work to be per- 
formed in the circulation, different supplies of nutrient substance must 
be presented to the motor organ, just as in the steam-engine the 
amount of fuel must be varied according to the work required from 
the machine. 
When the microscope revealed the existence of a well-marked 
muscular coat to the smaller systemic arteries, it became evident 
that the different diameters of those vessels consequent on the degrees 
of contraction of their walls, varied the amount of force necessary to 
propel the blood through them ; and these variations have been con- 
-siderably studied of late. Dr. Marey of Paris, the introducer of the 
sphygmograph, has, in his most scientific treatise “‘ On the Circulation 
‘of the Blood,”’+ strongly drawn attention to this subject, and he has 
worked ont a theory respecting the law regulating the frequency of 
the pulse, which is based mainly on the variations in arterial resist- 
ance. 
This theory of Marey’s it will be necessary to recapitulate here, 
and to examine the facts on which it rests. The following is the law 
in the two forms in which he gives it. 
1. “ The heart beats so much the more frequently, as it experi- 
ences less difficulty in emptying itself.” 
* This paper was originally printed and published separately (London: H. K. 
Lewis, 136, Gower Street, 1872), but was afterwards republished in the “Journal of 
Anatomy and Physiology,” VII. pp. 219-32, and VIII. pp. 54-61, with one or 
two corrections which have been here inserted.—Eb. 
+ “ Physiologie Medicale de la Circulation du Sang.” Paris, 1863. 
Page 2. 
