THE FREQUENCY OF THE PULSE. 59 
and shortens it, in other words, strengthens the heart, according to Page 24. 
the law that may be stated thus: the nutrition of the heart varies as 
the square root of the time during which the coronary circulation is 
maintained. 
It will strike some as peculiar that no mention has yet been made 
of the influence of the nervous system on the heart. But it appears 
to me that the facts which have been brought forward have not called 
for any special reference to it. May not the law it has been my 
endeavour to prove, be but an expression of that action in the healthy 
body ? For it must depend on a somewhat complicated mechanism, 
as is shown by the fact that it is almost impossible to contrive a 
self-acting engine which would pulsate in accordance with its require- 
ments. 
As is well known, the effect on the kymographion trace of slightly 
stimulating the pneumogastric nerves is greatly to amplify the oscil- 
lations, and at the same time to lower the mean pressure; while 
cutting the pneumogastrics produces the reverse effects. The larger 
oscillations of the hemadynamometer column in the former case show 
that the proportionate tension fall and the time of pulsation are both 
greatly increased, and from previous considerations it is evident that 
these are necessarily associated when, as now, no influence is being 
exerted on the peripheral vessels.* 
Further, these amplified oscillations must be attended with an Page 25. 
abnormal enlargement of the ventricular cavities during diastole, for 
the time intervening between the beats being increased, the amount 
of blood which flows through all segments of the circulation between 
any two pulsations must be also more considerable. Having arrived 
so far, it is extremely interesting to observe how an augmentation in 
the degree of cardiac dilatation during diastole, as a cause, will include 
and correlate all the peculiarities which are observed when the depres- 
sor nerve is thus operated on; and it is not unreasonable, therefore, 
to suppose that this is the direct effect of its action. As the quantity 
of blood contained in the heart at the end of diastole has been shown 
to depend on the circulation through the coronary vessels, it is evi- 
dent that the explanation of any variations in the capacity of the 
ventricles must be referred to changes in the cardiac walls themselves. 
Just as the degree of rigidity of an india-rubber tube through which 
a current of water is flowing, can be made to vary by changing the 
diameter of the orifice from which the fluid is allowed to escape, so 
the turgescence of the ventricular walls, or what is the same thing, 
* In rabbits the normal fall of tension as judged by the hemadynamometer trace 
is about =5th of the whole, while when the pneumogastric is stimulated it may 
increase to th or more. 
