THAT THERE IS A CIRCULATION OF THE BLOOD IS SHOWN FROM THE SECOND
POSITION DEMONSTRATED
If these things be so, another point which I have already referred to,
viz. the continual passage of the blood through the heart, will also be
confirmed. We have seen, that the blood passes from the arteries into
the veins, not from the veins into the arteries; we have seen, farther,
that almost the whole of the blood may be withdrawn from a puncture
made in one of the cutaneous veins of the arm if a bandage properly
applied be used; we have seen, still farther, that the blood flows
so freely and rapidly that not only is the whole quantity which was
contained in the arm beyond the ligature, and before the puncture was
made, discharged, but the whole which is contained in the body, both
that of the arteries and that of the veins.
Whence we must admit, first, that the blood is sent along with an
impulse, and that it is urged with force below the fillet; for it
escapes with force, which force it receives from the pulse and power
of the heart; for the force and motion of the blood are derived from
the heart alone. Second, that the afflux proceeds from the heart, and
through the heart by a course from the great veins [into the aorta];
for it gets into the parts below the ligature through the arteries,
not through the veins; and the arteries nowhere receive blood from the
veins, nowhere receive blood save and except from the left ventricle
of the heart. Nor could so large a quantity of blood be drawn from one
vein (a ligature having been duly applied), nor with such impetuosity,
such readiness, such celerity, unless through the medium of the
impelling power of the heart.
But if all things be as they are now represented, we shall feel
ourselves at liberty to calculate the quantity of the blood, and
to reason on its circular motion. Should any one, for instance, in
performing phlebotomy, suffer the blood to flow in the manner it
usually does, with force and freely, for some half-hour or so, no
question but that the greatest part of the blood being abstracted,
faintings and syncopes would ensue, and that not only would the
arteries but the great veins also be nearly emptied of their contents.
It is only consonant with reason to conclude that in the course of
the half-hour hinted at, so much as has escaped has also passed from
the great veins through the heart into the aorta. And further, if we
calculate how many ounces flow through one arm, or how many pass in
twenty or thirty pulsations under the medium ligature, we shall have
some grounds for estimating how much passes through the other arm
in the same space of time; how much through both lower extremities,
how much through the neck on either side, and through all the other
arteries and veins of the body, all of which have been supplied with
fresh blood, and as this blood must have passed through the lungs and
ventricles of the heart, and must have come from the great veins,--we
shall perceive that a circulation is absolutely necessary, seeing
that the quantities hinted at cannot be supplied immediately from
the ingesta, and are vastly more than can be requisite for the mere
nutrition of the parts.
It is still further to be observed, that the truths contended for
are sometimes confirmed in another way; for having tied up the arm
properly, and made the puncture duly, still, if from alarm or any other
causes, a state of faintness supervenes, in which the heart always
pulsates more languidly, the blood does not flow freely, but distils by
drops only. The reason is, that with the somewhat greater than usual
resistance offered to the transit of the blood by the bandage, coupled
with the weaker action of the heart, and its diminished impelling
power, the stream cannot make its way under the fillet; and farther,
owing to the weak and languishing state of the heart, the blood is not
transferred in such quantity as wont from the veins to the arteries
through the sinuses of that organ. So also, and for the same reasons,
are the menstrual fluxes of women, and indeed hemorrhagies of every
kind, controlled. And now, a contrary state of things occurring,
the patient getting rid of his fear and recovering his courage, the
pulsific power is increased, the arteries begin again to beat with
greater force, and to drive the blood even into the part that is bound;
so that the blood now springs from the puncture in the vein, and flows
in a continuous stream.