William Harvey, the discoverer of the circulation of the blood, was
born at Folkestone, England, on April 1, 1578. After graduating
from Caius College, Cambridge, he studied at Padua, where he had
the celebrated anatomist, Fabricius of Aquapendente, for his
master. In 1615 he was elected Lumleian lecturer at the College of
Physicians, and three years later was appointed physician
extraordinary to King James I. In 1628, twelve years after his
first statement of it in his lectures, he published at Frankfurt,
in Latin, "An Anatomical Disquisition on the Motion of the Heart
and Blood," in which he maintained that there is a circulation of
the blood. Moreover, he distinguished between the pulmonary
circulation, from the right side of the heart to the left through
the lungs, and the systemic circulation from the left side of the
heart to the right through the rest of the body. Further, he
maintained that it was the office of the heart to maintain this
circulation by its alternate _diastole_ (expansion) and _systole_
(contraction) throughout life. This discovery was, says Sir John
Simon, the most important ever made in physiological science. It is
recorded that after his publication of it Harvey lost most of his
practice. Harvey died on June 3, 1657.
_I.--Motions of the Heart in Living Animals_
When first I gave my mind to vivisections as a means of discovering the
motions and uses of the heart, I found the task so truly arduous that I
was almost tempted to think, with Fracastorius, that the motion of the
heart was only to be comprehended by God. For I could neither rightly
perceive at first when the systole and when the diastole took place, nor
when and where dilation and contraction occurred, by reason of the
rapidity of the motion, which, in many animals, is accomplished in the
twinkling of an eye, coming and going like a flash of lightning. At
length it appeared that these things happen together or at the same
instant: the tension of the heart, the pulse of its apex, which is felt
externally by its striking against the chest, the thickening of its
walls, and the forcible expulsion of the blood it contains by the
constriction of its ventricles.
Hence the very opposite of the opinions commonly received appears to be
true; inasmuch as it is generally believed that when the heart strikes
the breast and the pulse is felt without, the heart is dilated in its
ventricles and is filled with blood. But the contrary of this is the
fact; that is to say, the heart is in the act of contracting and being
emptied. Whence the motion, which is generally regarded as the diastole
of the heart, is in truth its systole. And in like manner the intrinsic
motion of the heart is not the diastole but the systole; neither is it
in the diastole that the heart grows firm and tense, but in the systole;
for then alone when tense is it moved and made vigorous. When it acts
and becomes tense the blood is expelled; when it relaxes and sinks
together it receives the blood in the manner and wise which will by and
by be explained.
From divers facts it is also manifest, in opposition to commonly
received opinions, that the diastole of the arteries corresponds with
the time of the heart's systole; and that the arteries are filled and
distended by the blood forced into them by the contraction of the
ventricles. It is in virtue of one and the same cause, therefore, that
all the arteries of the body pulsate, _viz._, the contraction of the
left ventricle in the same way as the pulmonary artery pulsates by the
contraction of the right ventricle.
I am persuaded it will be found that the motion of the heart is as
follows. First of all, the auricle contracts and throws the blood into
the ventricle, which, being filled, the heart raises itself straightway,
makes all its fibres tense, contracts the ventricles and performs a
beat, by which beat it immediately sends the blood supplied to it by the
auricle into the arteries; the right ventricle sending its charge into
the lungs by the vessel called _vena arteriosa_, but which, in structure
and function, and all things else, is an artery; the left ventricle
sending its charge into the aorta, and through this by the arteries to
the body at large.
The grand cause of hesitation and error in this subject appears to me to
have been the intimate connection between the heart and the lungs. When
men saw both the pulmonary artery and the pulmonary veins losing
themselves in the lungs, of course it became a puzzle to them to know
how the right ventricle should distribute the blood to the body, or the
left draw it from the _venæ cavæ_. Or they have hesitated because they
did not perceive the route by which the blood is transferred from the
veins to the arteries, in consequence of the intimate connection between
the heart and lungs. And that this difficulty puzzled anatomists not a
little when in their dissections they found the pulmonary artery and
left ventricle full of black and clotted blood, plainly appears when
they felt themselves compelled to affirm that the blood made its way
from the right to the left ventricle by sweating through the septum of
the heart.
Had anatomists only been as conversant with the dissection of the lower
animals as they are with that of the human body, the matters that have
hitherto kept them in perplexity of doubt would, in my opinion, have met
them freed from every kind of difficulty. And first in fishes, in which
the heart consists of but a single ventricle, they having no lungs, the
thing is sufficiently manifest. Here the sac, which is situated at the
base of the heart, and is the part analogous to the auricle in man,
plainly throws the blood into the heart, and the heart in its turn
conspicuously transmits it by a pipe or artery, or vessel analogous to
an artery; these are facts which are confirmed by simple ocular
experiment. I have seen, farther, that the same thing obtained most
obviously.
And since we find that in the greater number of animals, in all indeed
at a certain period of their existence, the channels for the
transmission of the blood through the heart are so conspicuous, we have
still to inquire wherefore in some creatures--those, namely, that have
warm blood and that have attained to the adult age, man among the
number--we should not conclude that the same thing is accomplished
through the substance of the lungs, which, in the embryo, and at a time
when the functions of these organs is in abeyance, Nature effects by
direct passages, and which indeed she seems compelled to adopt through
want of a passage by the lungs; or wherefore it should be better (for
Nature always does that which is best) that she should close up the
various open routes which she had formerly made use of in the embryo,
and still uses in all other animals; not only opening up no new apparent
channels for the passage of the blood therefore, but even entirely
shutting up those which formerly existed in the embryos of those animals
that have lungs. For while the lungs are yet in a state of inaction,
Nature uses the two ventricles of the heart as if they formed but one
for the transmission of the blood. The condition of the embryos of those
animals which have lungs is the same as that of those animals which have
no lungs.
Thus, by studying the structure of the animals who are nearer to and
further from ourselves in their modes of life and in the construction of
their bodies, we can prepare ourselves to understand the nature of the
pulmonary circulation in ourselves, and of the systemic circulation
also.
_II.--Systemic Circulation_
What remains to be said is of so novel and unheard of a character that I
not only fear injury to myself from the envy of a few, but I tremble
lest I have mankind at large for my enemies, so much do wont and custom
that become as another nature, and doctrine once sown that hath struck
deep root, and respect for antiquity, influence all men.
And, sooth to say, when I surveyed my mass of evidence, whether derived
from vivisections and my previous reflections on them, or from the
ventricles of the heart and the vessels that enter into and issue from
them, the symmetry and size of these conduits--for Nature, doing nothing
in vain, would never have given them so large a relative size without a
purpose; or from the arrangement and intimate structure of the valves in
particular and of the many other parts of the heart in general, with
many things besides; and frequently and seriously bethought me and long
revolved in my mind what might be the quantity of blood which was
transmitted, in how short a time its passage might be effected and the
like; and not finding it possible that this could be supplied by the
juices of the ingested aliment without the veins on the one hand
becoming drained, and the arteries on the other getting ruptured through
the excessive charge of blood, unless the blood should somehow find its
way from the arteries into the veins, and so return to the right side of
the heart; when I say, I surveyed all this evidence, I began to think
whether there might not be _a motion as it were in a circle_.
Now this I afterwards found to be true; and I finally saw that the
blood, forced by the action of the left ventricle into the arteries, was
distributed to the body at large, and its several parts, in the same
manner as it is sent through the lungs, impelled by the right ventricle
into the pulmonary artery; and that it then passed through the veins and
along the _vena cava_, and so round to the left ventricle in the manner
already indicated; which motion we may be allowed to call circular, in
the same way as Aristotle says that the air and the rain emulate the
circular motion of the superior bodies. For the moist earth, warmed by
the sun, evaporates; the vapours drawn upwards are condensed, and
descending in the form of rain moisten the earth again. And by this
arrangement are generations of living things produced; and in like
manner, too, are tempests and meteors engendered by the circular motion
of the sun.
And so in all likelihood does it come to pass in the body through the
motion of the blood. The various parts are nourished, cherished,
quickened by the warmer, more perfect, vaporous, spirituous, and, as I
may say, alimentive blood; which, on the contrary, in contact with these
parts becomes cooled, coagulated, and, so to speak, effete; whence it
returns to its sovereign, the heart, as if to its source, or to the
inmost home of the body, there to recover its state of excellence or
perfection. Here it resumes its due fluidity, and receives an infusion
of natural heat--powerful, fervid, a kind of treasury of life--and is
impregnated with spirits and, it might be said, with balsam; and thence
it is again dispersed. And all this depends upon the motion and action
of the heart.
_Confirmations of the Theory_
Three points present themselves for confirmation, which, being
established, I conceive that the truth I contend for will follow
necessarily and appear as a thing obvious to all.
The first point is this. 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 wise
that the whole mass must very quickly pass through the organ.
Let us assume the quantity of blood which the left ventricle of the
heart will contain when distended to be, say, two ounces (in the dead
body I have found it to contain upwards of two ounces); and let us
suppose, as approaching the truth, that the fourth part of its charge
is thrown into the artery at each contraction. Now, in the course of
half an hour the heart will have made more than one thousand beats.
Multiplying the number of drachms propelled by the number of pulses, we
shall have one thousand half-ounces sent from this organ into the
artery; a larger quantity than is contained in the whole body. 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.
The second point is this. 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.
I have here to cite certain experiments. Ligatures are either very tight
or of middling tightness. A ligature I designate as tight, or perfect,
when it is drawn so close about an extremity that no vessel can be felt
pulsating beyond it. Such ligatures are employed in the removal of
tumours; and in these cases, all afflux of nutriment and heat being
prevented by the ligature, we see the tumours dwindle and die, and
finally drop off. Now let anyone make an experiment upon the arm of a
man, either using such a fillet as is employed in bloodletting, or
grasping the limb tightly with his hand; let a ligature be thrown about
the extremity and drawn as tightly as can be borne. It will first be
perceived that beyond the ligature the arteries do not pulsate, while
above it the artery begins to rise higher at each diastole and to swell
with a kind of tide as it strove to break through and overcome the
obstacle to its current.
Then let the ligature be brought to that state of middling tightness
which is used in bleeding, and it will be seen that the hand and arm
will instantly become deeply suffused and extended, and the veins show
themselves tumid and knotted. Which is as much as to say that when the
arteries pulsate the blood is flowing through them, but where they do
not pulsate they cease from transmitting anything. The veins again being
compressed, nothing can flow through them; the certain indication of
which is that below the ligature they are much more tumid than above it.
Whence is this blood? It must needs arrive by the arteries. For that it
cannot flow in by the veins appears from the fact that the blood cannot
be forced towards the heart unless the ligature be removed. Further,
when we see the veins below the ligature instantly swell up and become
gorged when from extreme tightness it is somewhat relaxed, the arteries
meanwhile continuing unaffected, this is an obvious indication that the
blood passes from the arteries into the veins, and not from the veins
into the arteries, and that there is either an anastomosis of the two
orders of vessels, or pores in the flesh and solid parts generally that
are permeable to the blood.
And now we understand wherefore in phlebotomy we apply our fillet above
the part that is punctured, not below it. Did the flow come from above,
not from below, the bandage in this case would not only be of no
service, but would prove a positive hindrance. 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 perceive
that a circulation is absolutely necessary, seeing that the quantity
cannot be supplied immediately from the ingesta, and is vastly more than
can be requisite for the mere nutrition of the parts.
And the third point to be confirmed is this. That the veins return this
blood to the heart incessantly from all parts and members of the body.
This position will be made sufficiently clear from the valves which are
found in the cavities of the veins themselves, from the uses of these,
and from experiments cognisable by the senses. The celebrated Hieronymus
Fabricius, of Aquapendente, first gave representations of the valves in
the veins, which consist of raised or loose portions of the inner
membranes of these vessels of extreme delicacy and a sigmoid, or
semi-lunar shape. Their office is by no means explained when we are told
that it is to hinder the blood, by its weight, from flowing into
inferior parts; for the edges of the valves in the jugular veins hang
downwards, and are so contrived that they prevent the blood from rising
upwards.
The valves, in a word, do not invariably look upwards, but always
towards the trunks of the veins--towards the seat of the heart. They are
solely made and instituted lest, instead of advancing from the extreme
to the central parts of the body, the blood should rather proceed along
the veins from the centre to the extremities; but the delicate valves,
while they readily open in the right direction, entirely prevent all
such contrary motion, being so situated and arranged that if anything
escapes, or is less perfectly obstructed by the flaps of the one above,
the fluid passing, as it were, by the chinks between the flaps, it is
immediately received on the convexity of the one beneath, which is
placed transversely with reference to the former, and so is effectually
hindered from getting any farther. And this I have frequently
experienced in my dissections of veins. If I attempted to pass a probe
from the trunk of the veins into one of the smaller branches, whatever
care I took I found it impossible to introduce it far any way by reason
of the valves; whilst, on the contrary, it was most easy to push it
along in the opposite direction, from without inwards, or from the
branches towards the trunks and roots.
And now I may be allowed to give in brief my view of the circulation of
the blood, and to propose it for general adoption.
_The Conclusion_
Since all things, both argument and ocular demonstration, show that the
blood passes through the lungs and heart by the action of the
ventricles; and is sent for distribution to all parts of the body, where
it makes its way into the veins and pores of the flesh; and then flows
by the veins from the circumference on every side to the centre, from
the lesser to the greater veins; and is by them finally discharged into
the _vena cava_ and right auricle of the heart, and this in such a
quantity or in such a flux and reflux, thither by the arteries, hither
by the veins, as cannot possibly be supplied by the ingesta, and is much
greater than can be required for mere purposes of nutrition; therefore,
it is absolutely necessary to conclude that the blood in the animal body
is impelled in a circle and is in a state of ceaseless motion; and that
this is the act, or function, which the heart performs by means of its
pulse, and that it is the sole and only end of the motion and
contraction of the heart. For it would be very difficult to explain in
any other way to what purpose all is constructed and arranged as we have
seen it to be.