Harvey
CHAPTER
IX THAT
THERE IS A CIRCULATION OF THE BLOOD 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 that 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
in 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 nonnaturals,—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 tumours in the human subject. Nor
would this argument lose any 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 butcher 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.
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