THE SYSTOLE AND DIASTOLE.
185
that of the ventricles not being synchronous. In warm-blooded
animals the auricles contract immediately before the ventricle. In
the frog the contractions of the venous trunks, of the auricles, the
ventricle, and the bulbus aortæ, appeared to me to follow the order
in which I have specified the parts, the intervals between the four
contractions being nearly equal; so that the same interval of time
elapsed from the contraction of the auricles to the contraction of the
ventricle, as between the contraction of the ventricle and that of the
bulb of the aorta. I am convinced, from repeated observations, that
the auricles and ventricle do not, as Oesterreicher* asserts, alternate
in action at equal intervals, like the motions of the pendulum, but
that the time that intervenes between the contraction of the auricles
and the contraction of the ventricle is much less than that which
elapses from the moment of the contraction of the ventricle to the
moment when the auricles again act; and that generally the con¬
traction of the bulbus aortæ and venous trunks occur in the interval
of time last indicated. In warm-blooded animals I have seen the
contractions of the auricles cease altogether for some moments,
which must have been caused by the injury inflicted in making the
observation. Under ordinary circumstances, the auricular contrac¬
tion was always a very quick motion immediately preceding the
action of the ventricle, the interval of time from the contraction of
the auricles to the contraction of the ventricle being certainly very
much shorter than the period that elapsed between the contraction
of the ventricles and that of the auricles.
The contraction (systole) alone of the heart is an active state; the
dilatation (diastole) is the moment of repose, in which the fibres are
relaxed, and in which the blood is poured from the contiguous veins
into the cavities of the heart, to fill the vacuum consequent on the
relaxation of its fibres: the valves of the heart being so arranged as
to allow the influx of the blood from the veins. The dilatation of
the heart was supposed by Bichat, and some other French physiolo¬
gists, to be an active movement, but Oesterreichert has by a very
ingenious experiment refuted this supposition. He removed the
heart of a frog from the body, and laid upon it a substance sufficiently
heavy to press it flat, and yet so small as not to conceal the heart
from view; he then observed that during the contraction of the heart
the weight was raised, but that during its dilatation the heart re¬
mained flat. This experiment shows that the dilatation of the heart
is not a muscular act; at the same time, however, it must be recol¬
lected that the walls of the heart during life cannot become so relaxed
at the time of the diastole, as in a heart removed from the body, even
although the cavities of the heart were not filled with blood; for, in
the living state, the capillary vessels of its substance are at the time
of relaxation injected with blood, which, during the contraction, is
pressed out of them, and this filling of its vessels must give it some
degree of firmness and rigidity.
* Lehre vom Kreislauf des Blutes. Nürnb. 1826.
f Loc. cit. p. 33.
16*