Harvey
CHAPTER
X THE
FIRST POSITION: OF THE QUANTITY 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 noon-day 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 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 be
come 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 in 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.
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