THAT THERE IS A CIRCULATION OF THE BLOOD IS CONFIRMED FROM THE
FIRST PROPOSITION
But lest anyone should say that we give them words only, and make
mere specious assertions without any foundation, and desire to
innovate without sufficient cause, three points present
themselves for confirmation, which, being stated, I conceive that
the truth I contend for will follow necessarily, and appear as a
thing obvious to all. First, the blood is incessantly transmitted
by the action of the heart from the vena cava to the arteries in
such quantity that it cannot be supplied from the ingesta, and in
such a manner that the whole must very quickly pass through the
organ; second, the blood under the influence of the arterial
pulse enters and is impelled in a continuous, equable, and
incessant stream through every part and member of the body, in
much larger quantity than were sufficient for nutrition, or than
the whole mass of fluids could supply; third, the veins in like
manner return this blood incessantly to the heart from parts and
members of the body. These points proved, I conceive it will be
manifest that the blood circulates, revolves, propelled and then
returning, from the heart to the extremities, from the
extremities to the heart, and thus that it performs a kind of
circular motion.
Let us assume, either arbitrarily or from experiment, the
quantity of blood which the left ventricle of the heart will
contain when distended, to be, say, two ounces, three ounces, or
one ounce and a half--in the dead body I have found it to hold
upwards of two ounces. Let us assume further how much less the
heart will hold in the contracted than in the dilated state; and
how much blood it will project into the aorta upon each
contraction; and all the world allows that with the systole
something is always projected, a necessary consequence
demonstrated in the third chapter, and obvious from the structure
of the valves; and let us suppose as approaching the truth that
the fourth, or fifth, or sixth, or even but the eighth part of
its charge is thrown into the artery at each contraction; this
would give either half an ounce, or three drachms, or one drachm
of blood as propelled by the heart at each pulse into the aorta;
which quantity, by reason of the valves at the root of the
vessel, can by no means return into the ventricle. Now, in the
course of half an hour, the heart will have made more than one
thousand beats, in some as many as two, three, and even four
thousand. Multiplying the number of drachms propelled by the
number of pulses, we shall have either one thousand half ounces,
or one thousand times three drachms, or a like proportional
quantity of blood, according to the amount which we assume as
propelled with each stroke of the heart, sent from this organ
into the artery--a larger quantity in every case than is
contained in the whole body! In the same way, in the sheep or
dog, say but a single scruple of blood passes with each stroke of
the heart, in one half-hour we should have one thousand scruples,
or about three pounds and a half, of blood injected into the
aorta; but the body of neither animal contains above four pounds
of blood, a fact which I have myself ascertained in the case of
the sheep.
Upon this supposition, therefore, assumed merely as a ground for
reasoning, we see the whole mass of blood passing through the
heart, from the veins to the arteries, and in like manner through
the lungs.
But let it be said that this does not take place in half an hour,
but in an hour, or even in a day; any way, it is still manifest
that more blood passes through the heart in consequence of its
action, than can either be supplied by the whole of the ingesta,
or than can be contained in the veins at the same moment.
Nor can it be allowed that the heart in contracting sometimes
propels and sometimes does not propel, or at most propels but
very little, a mere nothing, or an imaginary something: all this,
indeed, has already been refuted, and is, besides, contrary both
to sense and reason. For if it be a necessary effect of the
dilatation of the heart that its ventricles become filled with
blood, it is equally so that, contracting, these cavities should
expel their contents; and this not in any trifling measure. For
neither are the conduits small, nor the contractions few in
number, but frequent, and always in some certain proportion,
whether it be a third or a sixth, or an eighth, to the total
capacity of the ventricles, so that a like proportion of blood
must be expelled, and a like proportion received with each stroke
of the heart, the capacity of the ventricle contracted always
bearing a certain relation to the capacity of the ventricle when
dilated. And since, in dilating, the ventricles cannot be
supposed to get filled with nothing, or with an imaginary
something, so in contracting they never expel nothing or aught
imaginary, but always a certain something, viz., blood, in
proportion to the amount of the contraction. Whence it is to be
concluded that if at one stroke the heart of man, the ox, or the
sheep, ejects but a single drachm of blood and there are one
thousand strokes in half an hour, in this interval there will
have been ten pounds five ounces expelled; if with each stroke
two drachms are expelled, the quantity would, of course, amount
to twenty pounds and ten ounces; if half an ounce, the quantity
would come to forty-one pounds and eight ounces; and were there
one ounce, it would be as much as eighty-three pounds and four
ounces; the whole of which, in the course of one-half hour, would
have been transfused from the veins to the arteries. The actual
quantity of blood expelled at each stroke of the heart, and the
circumstances under which it is either greater or less than
ordinary, I leave for particular determination afterwards, from
numerous observations which I have made on the subject.
Meantime this much I know, and would here proclaim to all, that
the blood is transfused at one time in larger, at another in
smaller, quantity; and that the circuit of the blood is
accomplished now more rapidly, now more slowly, according to the
temperament, age, etc., of the individual, to external and
internal circumstances, to naturals and non-naturals--sleep,
rest, food, exercise, affections of the mind, and the like. But,
supposing even the smallest quantity of blood to be passed
through the heart and the lungs with each pulsation, a vastly
greater amount would still be thrown into the arteries and whole
body than could by any possibility be supplied by the food
consumed. It could be furnished in no other way than by making a
circuit and returning.
This truth, indeed, presents itself obviously before us when we
consider what happens in the dissection of living animals; the
great artery need not be divided, but a very small branch only
(as Galen even proves in regard to man), to have the whole of the
blood in the body, as well that of the veins as of the arteries,
drained away in the course of no long time--some half-hour or
less. Butchers are well aware of the fact and can bear witness to
it; for, cutting the throat of an ox and so dividing the vessels
of the neck, in less than a quarter of an hour they have all the
vessels bloodless--the whole mass of blood has escaped. The same
thing also occasionally occurs with great rapidity in performing
amputations and removing tumors in the human subject.
Nor would this argument lose of its force, did any one say that
in killing animals in the shambles, and performing amputations,
the blood escaped in equal, if not perchance in larger quantity
by the veins than by the arteries. The contrary of this
statement, indeed, is certainly the truth; the veins, in fact,
collapsing, and being without any propelling power, and further,
because of the impediment of the valves, as I shall show
immediately, pour out but very little blood; whilst the arteries
spout it forth with force abundantly, impetuously, and as if it
were propelled by a syringe. And then the experiment is easily
tried of leaving the vein untouched and only dividing the artery
in the neck of a sheep or dog, when it will be seen with what
force, in what abundance, and how quickly, the whole blood in the
body, of the veins as well as of the arteries, is emptied. But
the arteries receive blood from the veins in no other way than by
transmission through the heart, as we have already seen; so that
if the aorta be tied at the base of the heart, and the carotid or
any other artery be opened, no one will now be surprised to find
it empty, and the veins only replete with blood.
And now the cause is manifest, why in our dissections we usually
find so large a quantity of blood in the veins, so little in the
arteries; why there is much in the right ventricle, little in the
left, which probably led the ancients to believe that the
arteries (as their name implies) contained nothing but spirits
during the life of an animal. The true cause of the difference is
perhaps this, that as there is no passage to the arteries, save
through the lungs and heart, when an animal has ceased to breathe
and the lungs to move, the blood in the pulmonary artery is
prevented from passing into the pulmonary veins, and from thence
into the left ventricle of the heart; just as we have already
seen the same transit prevented in the embryo, by the want of
movement in the lungs and the alternate opening, and shutting of
their hidden and invisible porosities and apertures. But the
heart not ceasing to act at the same precise moment as the lungs,
but surviving them and continuing to pulsate for a time, the left
ventricle and arteries go on distributing their blood to the body
at large and sending it into the veins; receiving none from the
lungs, however, they are soon exhausted, and left, as it were,
empty. But even this fact confirms our views, in no trifling
manner, seeing that it can be ascribed to no other than the cause
we have just assumed.
Moreover, it appears from this that the more frequently or
forcibly the arteries pulsate, the more speedily will the body be
exhausted of its blood during hemorrhage. Hence, also, it
happens, that in fainting fits and in states of alarm, when the
heart beats more languidly and less forcibly, hemorrhages are
diminished and arrested.
Still further, it is from this, that after death, when the heart
has ceased to beat, it is impossible, by dividing either the
jugular or femoral veins and arteries, by any effort, to force
out more than one-half of the whole mass of the blood. Neither
could the butchers ever bleed the carcass effectually did he
neglect to cut the throat of the ox which he has knocked on the
head and stunned, before the heart had ceased beating.
Finally, we are now in a condition to suspect wherefore it is
that no one has yet said anything to the purpose upon the
anastomosis of the veins and arteries, either as to where or how
it is effected, or for what purpose. I now enter upon the
investigation of the subject.