THE FIRST POSITION: OF THE QUANTITY OF BLOOD PASSING FROM THE
VEINS TO THE ARTERIES. AND THAT THERE IS A CIRCUIT OF THE BLOOD,
FREED FROM OBJECTIONS, AND FARTHER CONFIRMED BY EXPERIMENT
So far our first position is confirmed, whether the thing be
referred to calculation or to experiment and dissection, viz.,
that the blood is incessantly poured into the arteries in larger
quantities than it can be supplied by the food; so that the whole
passing over in a short space of time, it is matter of necessity
that the blood perform a circuit, that it return to whence it set
out.
But if anyone shall here object that a large quantity may pass
through and yet no necessity be found for a circulation, that all
may come from the meat and drink consumed, and quote as an
illustration the abundant supply of milk in the mammae--for a cow
will give three, four, and even seven gallons and more in a day,
and a woman two or three pints whilst nursing a child or twins,
which must manifestly be derived from the food consumed; it may
be answered that the heart by computation does as much and more
in the course of an hour or two.
And if not yet convinced, he shall still insist that when an
artery is divided, a preternatural route is, as it were, opened,
and that so the blood escapes in torrents, but that the same
thing does not happen in the healthy and uninjured body when no
outlet is made; and that in arteries filled, or in their natural
state, so large a quantity of blood cannot pass in so short a
space of time as to make any return necessary--to all this it may
be answered that, from the calculation already made, and the
reasons assigned, it appears that by so much as the heart in its
dilated state contains, in addition to its contents in the state
of constriction, so much in a general way must it emit upon each
pulsation, and in such quantity must the blood pass, the body
being entire and naturally constituted.
But in serpents, and several fishes, by tying the veins some way
below the heart you will perceive a space between the ligature
and the heart speedily to become empty; so that, unless you would
deny the evidence of your senses, you must needs admit the return
of the blood to the heart. The same thing will also plainly
appear when we come to discuss our second position.
Let us here conclude with a single example, confirming all that
has been said, and from which everyone may obtain conviction
through the testimony of his own eyes.
If a live snake be laid open, the heart will be seen pulsating
quietly, distinctly, for more than an hour, moving like a worm,
contracting in its longitudinal dimensions, (for it is of an
oblong shape), and propelling its contents. It becomes of a paler
colour in the systole, of a deeper tint in the diastole; and
almost all things else are seen by which I have already said that
the truth I contend for is established, only that here everything
takes place more slowly, and is more distinct. This point in
particular may be observed more clearly than the noonday sun: the
vena cava enters the heart at its lower part, the artery quits it
at the superior part; the vein being now seized either with
forceps or between the finger and the thumb, and the course of
the blood for some space below the heart interrupted, you will
perceive the part that intervenes between the fingers and the
heart almost immediately to become empty, the blood being
exhausted by the action of the heart; at the same time the heart
will become of a much paler colour, even in its state of
dilatation, than it was before; it is also smaller than at first,
from wanting blood: and then it begins to beat more slowly, so
that it seems at length as if it were about to die. But the
impediment to the flow of blood being removed, instantly the
colour and the size of the heart are restored.
If, on the contrary, the artery instead of the vein be compressed
or tied, you will observe the part between the obstacle and the
heart, and the heart itself, to become inordinately distended, to
assume a deep purple or even livid colour, and at length to be so
much oppressed with blood that you will believe it about to be
choked; but the obstacle removed, all things immediately return
to their natural state and colour, size, and impulse.
Here then we have evidence of two kinds of death: extinction from
deficiency, and suffocation from excess. Examples of both have
now been set before you, and you have had opportunity of viewing
the truth contended for with your own eyes in the heart.