OF 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 heart of 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, &c., that the heart, when it moves,
becomes of a paler colour, when quiescent of a deeper blood-red colour.
From these particulars it appeared 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 vigour and tenseness, and from soft become hard, prominent, and
thickened: 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 fourth observation preceding, in which we have seen
that the heart, by squeezing out the blood 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 shock is given], 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 line of its straight fibres, although the great Vesalius,
giving this notion countenance, quotes a bundle of osiers bound into 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 that
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.