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that almost the whole of the blood may be withdrawn from a puncture made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.