



Produced by Amy E. Zelmer





WILLIAM HARVEY AND THE DISCOVERY OF THE CIRCULATION OF THE BLOOD

By Thomas H. Huxley


[1]



I DESIRE this evening to give you some account of the life and labours
of a very noble Englishman--William Harvey.

William Harvey was born in the year 1578, and as he lived until the year
1657, he very nearly attained the age of 80. He was the son of a small
landowner in Kent, who was sufficiently wealthy to send this, his eldest
son, to the University of Cambridge; while he embarked the others in
mercantile pursuits, in which they all, as time passed on, attained
riches.

William Harvey, after pursuing his education at Cambridge, and taking
his degree there, thought it was advisable--and justly thought so, in
the then state of University education--to proceed to Italy, which
at that time was one of the great centres of intellectual activity in
Europe, as all friends of freedom hope it will become again, sooner or
later. In those days the University of Padua had a great renown;
and Harvey went there and studied under a man who was then very
famous--Fabricius of Aquapendente. On his return to England, Harvey
became a member of the College of Physicians in London, and entered into
practice; and, I suppose, as an indispensable step thereto, proceeded
to marry. He very soon became one of the most eminent members of the
profession in London; and, about the year 1616, he was elected by the
College of Physicians their Professor of Anatomy. It was while Harvey
held this office that he made public that great discovery of the
circulation of the blood and the movements of the heart, the nature of
which I shall endeavour by-and-by to explain to you at length. Shortly
afterwards, Charles the First having succeeded to the throne in 1625,
Harvey became one of the king's physicians; and it is much to the credit
of the unfortunate monarch--who, whatever his faults may have been,
was one of the few English monarchs who have shown a taste for art and
science--that Harvey became his attached and devoted friend as well
as servant; and that the king, on the other hand, did all he could to
advance Harvey's investigations. But, as you know, evil times came on;
and Harvey, after the fortunes of his royal master were broken,
being then a man of somewhat advanced years--over 60 years of age, in
fact--retired to the society of his brothers in and near London, and
among them pursued his studies until the day of his death. Harvey's
career is a life which offers no salient points of interest to the
biographer. It was a life devoted to study and investigation; and it
was a life the devotion of which was amply rewarded, as I shall have
occasion to point out to you, by its results.

Harvey, by the diversity, the variety, and the thoroughness of his
investigations, was enabled to give an entirely new direction to at
least two branches--and two of the most important branches--of what
now-a-days we call Biological Science. On the one hand, he founded
all our modern physiology by the discovery of the exact nature of the
motions of the heart, and of the course in which the blood is propelled
through the body; and, on the other, he laid the foundation of that
study of development which has been so much advanced of late years, and
which constitutes one of the great pillars of the doctrine of evolution.
This doctrine, I need hardly tell you, is now tending to revolutionise
our conceptions of the origin of living things, exactly in the same
way as Harvey's discovery of the circulation in the seventeeth century
revolutionised the conceptions which men had previously entertained with
regard to physiological processes.

It would, I regret, be quite impossible for me to attempt, in the course
of the time I can presume to hold you here, to unfold the history of
more than one of these great investigations of Harvey. I call them
"great investigations," as distinguished from "large publications." I
have in my hand a little book, which those of you who are at a great
distance may have some difficulty in seeing, and which I value very
much. It is, I am afraid, sadly thumbed and scratched with annotations
by a very humble successor and follower of Harvey. This little book is
the edition of 1651 of the 'Exercitationes de Generatione'; and if you
were to add another little book, printed in the same small type, and
about one-seventh of the thickness, you would have the sum total of the
printed matter which Harvey contributed to our literature. And yet
in that sum total was contained, I may say, the materials of two
revolutions in as many of the main branches of biological science. If
Harvey's published labours can be condensed into so small a compass, you
must recollect that it is not because he did not do a great deal more.
We know very well that he did accumulate a very considerable number of
observations on the most varied topics of medicine, surgery, and natural
history. But, as I mentioned to you just now, Harvey, for a time, took
the royal side in the domestic quarrel of the Great Rebellion, as it
is called; and the Parliament, not unnaturally resenting that action of
his, sent soldiers to seize his papers. And while I imagine they found
nothing treasonable among those papers, yet, in the process of rummaging
through them, they destroyed all the materials which Harvey had spent a
laborious life in accumulating; and hence it is that the man's work and
labours are represented by so little in apparent bulk.

What I chiefly propose to do to-night is to lay before you an account of
the nature of the discovery which Harvey made, and which is termed the
Discovery of the Circulation of the Blood. And I desire also, with
some particularity, to draw your attention to the methods by which that
discovery was achieved; for, in both these respects, I think, there will
be much matter for profitable reflection.

Let me point out to you, in the first place, with respect to this
important matter of the movements of the heart and the course of the
blood in the body, that there is a certain amount of knowledge
which must have been obtained without men taking the trouble to seek
it--knowledge which must have been taken in, in the course of time,
by everybody who followed the trade of a butcher, and still more so by
those people who, in ancient times, professed to divine the course of
future events from the entrails of animals. It is quite obvious to
all, from ordinary accidents, that the bodies of all the higher animals
contain a hot red fluid--the blood. Everybody can see upon the surface
of some part of the skin, underneath that skin, pulsating tubes, which
we know as the arteries. Everybody can see under the surface of the skin
more delicate and softer looking tubes, which do not pulsate, which are
of a bluish colour, and are termed the veins. And every person who has
seen a recently killed animal opened knows that these two kinds of tubes
to which I have just referred, are connected with an apparatus which
is placed in the chest, which apparatus, in recently killed animals,
is still pulsating. And you know that in yourselves you can feel the
pulsation of this organ, the heart, between the fifth and sixth ribs. I
take it that this much of anatomy and physiology has been known from the
oldest times, not only as a matter of curiosity, but because one of the
great objects of men, from their earliest recorded existence, has been
to kill one another, and it was a matter of considerable importance to
know which was the best place for hitting an enemy. I can refer you to
very ancient records for most precise and clear information that one of
the best places is to smite him between the fifth and sixth ribs. Now
that is a very good piece of regional anatomy, for that is the place
where the heart strikes in its pulsations, and the use of smiting there
is that you go straight to the heart. Well, all that must have been
known from time immemorial--at least for 4,000 or 5,000 years before the
commencement of our era--because we know that for as great a period as
that the Egyptians, at any rate, whatever may have been the case with
other people, were in the enjoyment of a highly developed civilisation.
But of what knowledge they may have possessed beyond this we know
nothing; and in tracing back the springs of the origin of everything
that we call "modern science" (which is not merely knowing, but knowing
systematically, and with the intention and endeavour to find out
the causal connection of things)--I say that when we trace back the
different lines of all the modern sciences we come at length to one
epoch and to one country--the epoch being about the fourth and fifth
centuries before Christ, and the country being ancient Greece. It is
there that we find the commencement and the root of every branch of
physical science and of scientific method. If we go back to that time
we have in the works attributed to Aristotle, who flourished between 300
and 400 years before Christ, a sort of encyclopaedia of the scientific
knowledge of that day--and a very marvellous collection of, in many
respects, accurate and precise knowledge it is. But, so far as regards
this particular topic, Aristotle, it must be confessed, has not got very
far beyond common knowledge. He knows a little about the structure of
the heart. I do not think that his knowledge is so inaccurate as many
people fancy, but it does not amount to much. A very few years after his
time, however, there was a Greek philosopher, Erasistratus, who lived
about three hundred years before Christ, and who must have pursued
anatomy with much care, for he made the important discovery that there
are membranous flaps, which are now called "valves," at the origins
of the great vessels; and that there are certain other valves in the
interior of the heart itself.

Fig. 1.--The apparatus of the circulation, as at present known. The
capillary vessels, which connect the arteries and veins, are omitted, on
account of their small size. The shading of the "venous system" is given
to all the vessels which contain venous blood; that of the "arterial
system" to all the vessels which contain arterial blood.

I have here (Fig. 1) a purposely rough, but, so far as it goes,
accurate, diagram of the structure of the heart and the course of the
blood. The heart is supposed to be divided into two portions. It would
be possible, by very careful dissection, to split the heart down the
middle of a partition, or so-called'septum', which exists in it, and to
divide it into the two portions which you see here represented; in which
case we should have a left heart and a right heart, quite distinct from
one another. You will observe that there is a portion of each heart
which is what is called the ventricle. Now the ancients applied the term
'heart' simply and solely to the ventricles. They did not count the rest
of the heart--what we now speak of as the 'auricles'--as any part of the
heart at all; but when they spoke of the heart they meant the left and
the right ventricles; and they described those great vessels, which we
now call the 'pulmonary veins' and the'vena cava', as opening directly
into the heart itself.

What Erasistratus made out was that, at the roots of the aorta and
the pulmonary artery (Fig. 1) there were valves, which opened in the
direction indicated by the arrows; and, on the other hand, that at the
junction of what he called the veins with the heart there were other
valves, which also opened again in the direction indicated by the
arrows. This was a very capital discovery, because it proved that if
the heart was full of fluid, and if there were any means of causing that
fluid in the ventricles to move, then the fluid could move only in
one direction; for you will observe that, as soon as the fluid is
compressed, the two valves between the ventricles and the veins will be
shut, and the fluid will be obliged to move into the arteries; and,
if it tries to get back from them into the heart, it is prevented from
doing so by the valves at the origin of the arteries, which we now
call the semilunar valves (half-moon shaped valves); so that it is
impossible, if the fluid move at all, that it should move in any other
way than from the great veins into the arteries. Now that was a very
remarkable and striking discovery.

But it is not given to any man to be altogether right (that is a
reflection which it is very desirable for every man who has had the good
luck to be nearly right once, always to bear in mind); and Erasistratus,
while he made this capital and important discovery, made a very capital
and important error in another direction, although it was a very natural
error. If, in any animal which is recently killed, you open one of those
pulsating trunks which I referred to a short time ago, you will find, as
a general rule, that it either contains no blood at all or next to none;
but that, on the contrary, it is full of air. Very naturally, therefore,
Erasistratus came to the conclusion that this was the normal and natural
state of the arteries, and that they contained air. We are apt to think
this a very gross blunder; but, to anybody who is acquainted with
the facts of the case, it is, at first sight, an exceedingly natural
conclusion. Not only so, but Erasistratus might have very justly
imagined that he had seen his way to the meaning of the connection of
the left side of the heart with the lungs; for we find that what we now
call the pulmonary vein is connected with the lungs, and branches out in
them (Fig. 1). Finding that the greater part of this system of vessels
was filled with air after death, this ancient thinker very shrewdly
concluded that its real business was to receive air from the lungs, and
to distribute that air all through the body, so as to get rid of the
grosser humours and purify the blood. That was a very natural and very
obvious suggestion, and a highly ingenious one, though it happened to be
a great error. You will observe that the only way of correcting it was
to experiment upon living animals, for there is no other way in which
this point could be settled.

Fig.2,--The Course of the Blood according to Galen (A.D. 170).

And hence we are indebted, for the correction of the error of
Erasistratus, to one of the greatest experimenters of ancient or modern
times, Claudius Galenus, who lived in the second century after Christ. I
say it was to this man more than any one else, because he knew that the
only way of solving physiological problems was to examine into the facts
in the living animal. And because Galen was a skilful anatomist, and
a skilful experimenter, he was able to show in what particulars
Erasistratus had erred, and to build up a system of thought upon this
subject which was not improved upon for fully 1,300 years. I have
endeavoured, in Fig. 2, to make clear to you exactly what it was he
tried to establish. You will observe that this diagram is practically
the same as that given in Fig. 1, only simplified. The same facts may
be looked upon by different people from different points of view. Galen
looked upon these facts from a very different point of view from that
which we ourselves occupy; but, so far as the facts are concerned, they
were the same for him as for us. Well then, the first thing that Galen
did was to make out experimentally that, during life, the arteries are
not full of air, but that they are full of blood. And he describes a
great variety of experiments which he made upon living animals with the
view of proving this point, which he did prove effectually and for all
time; and that you will observe was the only way of settling the matter.
Furthermore, he demonstrated that the cavities of the left side of the
heart--what we now call the left auricle and the left ventricle--are,
like the arteries, full of blood during life, and that that blood was of
the scarlet kind--arterialised, or as he called it "pneumatised," blood.
It was known before, that the pulmonary artery, the right ventricle,
and the veins, contain the darker kind of blood, which was thence called
venous. Having proved that the whole of the left side of the heart,
during life, is full of scarlet arterial blood, Galen's next point
was to inquire into the mode of communication between the arteries
and veins. It was known before his time that both arteries and veins
branched out. Galen maintained, though he could not prove the fact, that
the ultimate branches of the arteries and veins communicated together
somehow or other, by what he called 'anastomoses', and that these
'anastomoses' existed not only in the body in general but also in the
lungs. In the next place, Galen maintained that all the veins of
the body arise from the liver; that they draw the blood thence and
distribute it over the body. People laugh at that notion now-a-days; but
if anybody will look at the facts he will see that it is a very probable
supposition. There is a great vein (hepatic vein--Fig. 1) which rises
out of the liver, and that vein goes straight into the'vena cava' (Fig.
1) which passes to the heart, being there joined by the other veins
of the body. The liver itself is fed by a very large vein (portal
vein--Fig. 1), which comes from the alimentary canal. The way the
ancients looked at this matter was, that the food, after being received
into the alimentary canal, was then taken up by the branches of this
great vein, which are called the'vena portae', just as the roots of a
plant suck up nourishment from the soil in which it lives; that then it
was carried to the liver, there to be what was called "concocted," which
was their phrase for its conversion into substances more fitted for
nutrition than previously existed in it. They then supposed that the
next thing to be done was to distribute this fluid through the body; and
Galen like his predecessors, imagined that the "concocted" blood, having
entered the great'vena cava', was distributed by its ramifications all
over the body. So that, in his view (Fig. 2), the course of the blood
was from the intestine to the liver, and from the liver into the great
'vena cava', including what we now call the right auricle of the heart,
whence it was distributed by the branches of the veins. But the whole of
the blood was not thus disposed of. Part of the blood, it was supposed,
went through what we now call the pulmonary arteries (Fig. 1), and,
branching out there, gave exit to certain "fuliginous" products, and
at the same time took in from the air a something which Galen calls the
'pneuma'. He does not know anything about what we call oxygen; but it
is astonishing how very easy it would be to turn his language into the
equivalent of modern chemical theory. The old philosopher had so just
a suspicion of the real state of affairs that you could make use of his
language in many cases, if you substituted the word "oxygen," which we
now-a-days use, for the word 'pneuma'. Then he imagined that the blood,
further concocted or altered by contact with the 'pneuma', passed to
a certain extent to the left side of the heart. So that Galen believed
that there was such a thing as what is now called the pulmonary
circulation. He believed, as much as we do, that the blood passed
through the right side of the heart, through the artery which goes to
the lungs, through the lungs themselves, and back by what we call the
pulmonary veins to the left side of the heart. But he thought it was
only a very small portion of the blood which passes to the right side of
the heart in this way; the rest of the blood, he thought, passed through
the partition which separates the two ventricles of the heart. He
describes a number of small pits, which really exist there, as holes,
and he supposed that the greater part of the blood passed through these
holes from the right to the left ventricle (Fig 2).

It is of great importance you should clearly understand these teachings
of Galen, because, as I said just now, they sum up all that anybody knew
until the revival of learning; and they come to this--that the blood
having passed from the stomach and intestines through the liver, and
having entered the great veins, was by them distributed to every part of
the body; that part of the blood, thus distributed, entered the arterial
system by the 'anastomoses', as Galen called them, in the lungs; that
a very small portion of it entered the arteries by the 'anastomoses' in
the body generally; but that the greater part of it passed through the
septum of the heart, and so entered the left side and mingled with the
pneumatised blood, which had been subjected to the air in the lungs,
and was then distributed by the arteries, and eventually mixed with the
currents of blood, coming the other way, through the veins.

Yet one other point about the views of Galen. He thought that both the
contractions and dilatations of the heart--what we call the'systole'
or contraction of the heart, and the 'diastole' or dilatation--Galen
thought that these were both active movements; that the heart actively
dilated, so that it had a sort of sucking power upon the fluids which
had access to it. And again, with respect to the movements of the pulse,
which anybody can feel at the wrist and elsewhere, Galen was of opinion
that the walls of the arteries partook of that which he supposed to be
the nature of the walls of the heart, and that they had the power of
alternately actively contracting and actively dilating, so that he is
careful to say that the nature of the pulse is comparable, not to the
movement of a bag, which we fill by blowing into it, and which we empty
by drawing the air out of it, but to the action of a bellows, which is
actively dilated and actively compressed.

Fig 3.--The course of the blood from the right to the left side of the
heart (Realdus Columbus, 1559).

After Galen's time came the collapse of the Roman Empire, the extinction
of physical knowledge, and the repression of every kind of scientific
inquiry, by its powerful and consistent enemy, the Church; and that
state of things lasted until the latter part of the Middle Ages saw the
revival of learning. That revival of learning, so far as anatomy
and physiology are concerned, is due to the renewed influence of
the philosophers of ancient Greece, and indeed, of Galen. Arabic
commentators had translated Galen, and portions of his works had got
into the language of the learned in the Middle Ages, in that way;
but, by the study of the classical languages, the original text became
accessible to the men who were then endeavouring to learn for themselves
something about the facts of nature. It was a century or more before
these men, finding themselves in the presence of a master--finding that
all their lives were occupied in attempting to ascertain for themselves
that which was familiar to him--I say it took the best part of a hundred
years before they could fairly see that their business was not to follow
him, but to follow his example--namely, to look into the facts of nature
for themselves, and to carry on, in his spirit, the work he had begun.
That was first done by Vesalius, one of the greatest anatomists who ever
lived; but his work does not specially bear upon the question we are
now concerned with. So far as regards the motions of the heart and the
course of the blood, the first man in the Middle Ages, and indeed the
only man who did anything which was of real importance, was one Realdus
Columbus, who was professor at Padua in the year 1559, and published a
great anatomical treatise. What Realdus Columbus did was this; once
more resorting to the method of Galen, turning to the living animal,
experimenting, he came upon new facts, and one of these new facts was
that there was not merely a subordinate communication between the blood
of the right side of the heart and that of the left side of the heart,
through the lungs, but that there was a constant steady current of
blood, setting through the pulmonary artery on the right side, through
the lungs, and back by the pulmonary veins to the left side of the heart
(Fig.3). Such was the capital discovery and demonstration of Realdus
Columbus. He is the man who discovered what is loosely called the
'pulmonary circulation'; and it really is quite absurd, in the face of
the fact, that twenty years afterwards we find Ambrose Pare, the great
French surgeon, ascribing this discovery to him as a matter of common
notoriety, to find that attempts are made to give the credit of it to
other people. So far as I know, this discovery of the course of the
blood through the lungs, which is called the pulmonary circulation, is
the one step in real advance that was made between the time of Galen
and the time of Harvey. And I would beg you to note that the word
"circulation" is improperly employed when it is applied to the course of
the blood through the lungs. The blood from the right side of the
heart, in getting to the left side of the heart, only performs a
half-circle--it does not perform a whole circle--it does not return
to the place from whence it started; and hence the discovery of the
so-called "pulmonary circulation" has nothing whatever to do with that
greater discovery which I shall point out to you by-and-by was made
by Harvey, and which is alone really entitled to the name of the
circulation of the blood.

If anybody wants to understand what Harvey's great desert really was,
I would suggest to him that he devote himself to a course of reading,
which I cannot promise shall be very entertaining, but which, in this
respect at any rate, will be highly instructive--namely, the works of
the anatomists of the latter part of the 16th century and the beginning
of the 17th century. If anybody will take the trouble to do that which
I have thought it my business to do, he will find that the doctrines
respecting the action of the heart and the motion of the blood which
were taught in every university in Europe, whether in Padua or in Paris,
were essentially those put forward by Galen, 'plus' the discovery of the
pulmonary course of the blood which had been made by Realdus Columbus.
In every chair of anatomy and physiology (which studies were not then
separated) in Europe, it was taught that the blood brought to the liver
by the portal vein, and carried out of the liver to the'vena cava'
by the hepatic vein, is distributed from the right side of the heart,
through the other veins, to all parts of the body; that the blood of the
