ON THE MOTIONS OF THE HEART AS SEEN IN THE DISSECTION OF LIVING
ANIMALS
In the first place, then, when the chest of a living animal is
laid open and the capsule that immediately surrounds the heart is
slit up or removed, the organ is seen now to move, now to be at
rest; there is a time when it moves, and a time when it is
motionless.
These things are more obvious in the colder animals, such as
toads, frogs, serpents, small fishes, crabs, shrimps, snails, and
shell-fish. They also become more distinct in warm-blooded
animals, such as the dog and hog, if they be attentively noted
when the heart begins to flag, to move more slowly, and, as it
were, to die: the movements then become slower and rarer, the
pauses longer, by which it is made much more easy to perceive and
unravel what the motions really are, and how they are performed.
In the pause, as in death, the heart is soft, flaccid, exhausted,
lying, as it were, at rest.
In the motion, and interval in which this is accomplished, three
principal circumstances are to be noted:
1. That the heart is erected, and rises upwards to a point, so
that at this time it strikes against the breast and the pulse is
felt externally.
2. That it is everywhere contracted, but more especially towards
the sides so that it looks narrower, relatively longer, more
drawn together. The heart of an eel taken out of the body of the
animal and placed upon the table or the hand, shows these
particulars; but the same things are manifest in the hearts of
all small fishes and of those colder animals where the organ is
more conical or elongated.
3. The heart being grasped in the hand, is felt to become harder
during its action. Now this hardness proceeds from tension,
precisely as when the forearm is grasped, its tendons are
perceived to become tense and resilient when the fingers are
moved.
4. It may further be observed in fishes, and the colder blooded
animals, such as frogs, serpents, etc., that the heart, when it
moves, becomes of a paler color, when quiescent of a deeper
blood-red color.
From these particulars it appears evident to me that the motion
of the heart consists in a certain universal tension--both
contraction in the line of its fibres, and constriction in every
sense. It becomes erect, hard, and of diminished size during its
action; the motion is plainly of the same nature as that of the
muscles when they contract in the line of their sinews and
fibres; for the muscles, when in action, acquire vigor and
tenseness, and from soft become hard, prominent, and thickened:
and in the same manner the heart.
We are therefore authorized to conclude that the heart, at the
moment of its action, is at once constricted on all sides,
rendered thicker in its parietes and smaller in its ventricles,
and so made apt to project or expel its charge of blood. This,
indeed, is made sufficiently manifest by the preceding fourth
observation in which we have seen that the heart, by squeezing
out the blood that it contains, becomes paler, and then when it
sinks into repose and the ventricle is filled anew with blood,
that the deeper crimson colour returns. But no one need remain in
doubt of the fact, for if the ventricle be pierced the blood will
be seen to be forcibly projected outwards upon each motion or
pulsation when the heart is tense.
These things, therefore, happen together or at the same instant:
the tension of the heart, the pulse of its apex, which is felt
externally by its striking against the chest, the thickening of
its parietes, and the forcible expulsion of the blood it contains
by the constriction of its ventricles.
Hence the very opposite of the opinions commonly received appears
to be true; inasmuch as it is generally believed that when the
heart strikes the breast and the pulse is felt without, the heart
is dilated in its ventricles and is filled with blood; but the
contrary of this is the fact, and the heart, when it contracts
(and the impulse of the apex is conveyed through the chest wall),
is emptied. Whence the motion which is generally regarded as the
diastole of the heart, is in truth its systole. And in like
manner the intrinsic motion of the heart is not the diastole but
the systole; neither is it in the diastole that the heart grows
firm and tense, but in the systole, for then only, when tense, is
it moved and made vigorous.
Neither is it by any means to be allowed that the heart only
moves in the lines of its straight fibres, although the great
Vesalius giving this notion countenance, quotes a bundle of
osiers bound in a pyramidal heap in illustration; meaning, that
as the apex is approached to the base, so are the sides made to
bulge out in the fashion of arches, the cavities to dilate, the
ventricles to acquire the form of a cupping-glass and so to suck
in the blood. But the true effect of every one of its fibres is
to constringe the heart at the same time they render it tense;
and this rather with the effect of thickening and amplifying the
walls and substance of the organ than enlarging its ventricles.
And, again, as the fibres run from the apex to the base, and draw
the apex towards the base, they do not tend to make the walls of
the heart bulge out in circles, but rather the contrary; inasmuch
as every fibre that is circularly disposed, tends to become
straight when it contracts; and is distended laterally and
thickened, as in the case of muscular fibres in general, when
they contract, that is, when they are shortened longitudinally,
as we see them in the bellies of the muscles of the body at
large. To all this let it be added, that not only are the
ventricles contracted in virtue of the direction and condensation
of their walls, but farther, that those fibres, or bands, styled
nerves by Aristotle, which are so conspicuous in the ventricles
of the larger animals, and contain all the straight fibres (the
parietes of the heart containing only circular ones), when they
contract simultaneously by an admirable adjustment all the
internal surfaces are drawn together as if with cords, and so is
the charge of blood expelled with force.
Neither is it true, as vulgarly believed, that the heart by any
dilatation or motion of its own, has the power of drawing the
blood into the ventricles; for when it acts and becomes tense,
the blood is expelled; when it relaxes and sinks together it
receives the blood in the manner and wise which will by-and-by be
explained.