The Circulation of the Blood
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Thomas H. Huxley >> The Circulation of the Blood
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WILLIAM HARVEY AND THE DISCOVERY OF THE CIRCULATION OF THE BLOOD
by Thomas H. Huxley
THE CIRCULATION OF THE BLOOD*
[*footnote] A Lecture delivered in the Free Trade Hall, November 2nd,
1878.
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.