FROM THE HUMAN CHEST-WALL. 21- 
until the closure of the mitral and tricuspid valves at b. From this: 
point, until the opening of the aortic and pulmonary yalves, the 
heart’s force is expended in raising the potential of its contained blood 
to that of the large arteries, and it is-a well-known fact that during 
that time the form of the ventricles becomes somewhat globular, their 
diameter increasing and thus causing them to recede in their conical © 
pericardial cavity, producing the fall b in the quick pulses. 
Immediately the semilunar valves get opened, the ventricles dis- 
tend the proximal parts of the large arteries, and it is evident, from 
a what has been said above with regard to the relation of blood potential 
* and rapidity, that the quicker the pulse the more relaxed is the aorta 
at the moment before the semilunar valves open; consequently, the 
more rapid the pulse the greater is the disturbance of equilibrium 
when they do so; and as the aorta gets stretched and lengthened by Page 21. 
the sudden repletion, so it sends the heart forward at that moment, 
causing the rise d, which must therefore be greater as the pulse is 
quicker, which is the case. In very slow pulses the blood potential 
being high, the repletion of the already greatly distended arteries does 
little in further filling them, but acts by sending the whole mass of 
blood forward ; consequently the rise d is inconsiderable. The rise ¢, 
if not resulting from the shock of closure of the auriculo-ventricular 
valves, must remain unexplained. 
The repletion of the proximal arteries is very rapid; and the 
accompanying rise is overcome in quick pulses by the speedy retreat 
of the apex, resulting from the emptying of the heart, causing the 
fall d, at the end of which the ventricles cease contracting. 
In slow pulses the heart’s systolé is prolonged, causing slight irre- 
gularities in the upward tending trace, which are fairly constant (e, 
which is frequently double). 
There is evidently an appreciable interval between the end of the 
ventricular systulé and the closure of the semilunar valves, during 
which the retrograde blood-current is arriving at sufficient velocity to 
enable them to act; but if Marey’s law of the relation of blood poten- 
tial and rapidity of heart’s action is correct, we are justified in going 
much further, and saying that the quicker the pulse, the more slowly do 
the aortic valves close; for the greater the blood potential, the sooner 
does the heartward current become sufficiently rapid to close the 
valves, whose hydrodynamical relations are not otherwise modified by 
the rate. 
From these considerations, combined with the fact, in quick pulses, 
that just before the rise f originates the trace loses its jerky character, 
it is most probable that the ventricles cease contracting just before the 
commencing rise f (at the end of the fall d in Figs. I, II), and that 
the whole of the time occupied by the rise and fall f is employed in 
