Classics of Scientific Method

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THE DISCOVERY Oi£ '6/

THE

CIRCULATION
OF THE BLOOD

Charles Singer

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Marine Biological Laboratory Library

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CLASSICS OF SCIENTIFIC METHOD

Edited by E. R. THOMAS, M.A., M.Sc.,

Headmaster of the Royal Grammar School,

Newcastle -on -Tyne

THE DISCOVERY OF
THE CIRCULATION OF THE BLOOD

Among other volumes to be included in
"Classics of Scientific Method" are
one dealing with " The Discovery of
the Nature of the Air, and of its
Changes during Breathing," by Miss
Clara M. Taylor, B.Sc. (Headmistress
of the Northampton High School and
late Senior Science Mistress at St.
Paul's Girls' School] ; and a volume
on " The Impossibility of Perpetual
Motion" by Mr. Alec. Wood, M.A.,
fellow of Emmanuel College,
Cambridge.

THE DISCOVERY OF

THE CIRCULATION

OF THE BLOOD

BY

CHARLES SINGER, M.D., D.LITT., F.R.C.P.

LECTURER IN THE HISTORY OF MEDICINE, LONDON UNIVERSITY

(UNIVERSITY COLLEGE)

LECTURER IN THE HISTORY OF THE BIOLOGICAL SCIENCES
OXFORD UNIVERSITY

LONDON

G. BELL AND SONS LTD.

1922

CLASSICS OF SCIENTIFIC METHOD
GENERAL INTRODUCTION

" Sachez egalement Messieurs . . . que la science dans notre
siecle, est Tame de la prospe*rite des nations et la source vive de
tout progres ! Sans doute, la politique avec ses fatigantes et quoti-
diennes discussions semble etre notre guide . . . vaine apparence !
Ce qui nous mene ce sont quelques decouvertes scientifiques et
leurs applications." — PASTEUR.

THE manifold activities of the human mind in its attempt
to comprehend the universe have left us a glorious
heritage. The student, be he youth or adult, who wishes
to trace the growth of understanding in Music, in Litera-
ture, or in the graphic arts, finds no lack of guidance.
Excellent reproductions of the great masterpieces of
painting or of sculpture can be obtained at small cost
in volumes where the improvement in technique and the
development of new ideas are indicated by a friendly
hand. Scientific invention has made the study of great
masterpieces of music possible to all, and there is now
growing up an adequate library of musical appreciation ;
while the great works of literature probably suffer from
over-interpretation.

The masterpieces of Science are not, however, so ac-
cessible to those who must of necessity dwell in the outer
courts of her temple. The Alembic Club reprints,
Ostwald's Klassiker, and Messrs. Gauthier-Villars's Les
Maitres de la Pensee Scientifique provide the specialist in
various branches of science with convenient copies of

vi CLASSICS OF SCIENTIFIC METHOD

epoch-making scientific papers, but they do not help the
layman. Many educated men and women of to-day feel
a desire to know more about the scientific interpretation
of the external world. The specialist in one branch of
science is little more than a layman in others, and he too
desires a wider acquaintance with the working of the
scientific spirit throughout the ages. The enlightened
teacher of science realises that he has failed in his duty
if he has done no more than communicate certain
scientific facts to his pupils. There is, in short, a de-
mand for a new literature of scientific appreciation.

The aim of this series is to provide reproductions of
the great masterpieces of science in convenient form,
together with a complete account of the action and re-
action of ideas which, through the process of time, led
up to the crucial experiments carried out and described
by some great master. Biographical details will be
introduced, and an attempt will be made to show the
various social and other influences as they assist or retard
the growth of knowledge. It is hoped that a reader
who takes up a volume of the series, dealing with a branch
of science of which he is ignorant, will be able, without
further aid, to trace the steps by which the human mind
has passed from chaotic ignorance to ordered knowledge.

E. R. T.

NEWCASTLE-ON-TYNE.

CONTENTS

PAGE

I. THE CIRCULATION OF THE BLOOD . i

II. THE KNOWLEDGE OF THE VASCULAR SYSTEM IN

ANTIQUITY . . . . . .10

III. THE REVIVAL OF LEARNING . . . .18

IV. VESALIUS AND THE NEW ANATOMY . . .23
V. SERVETUS . . . . . .29

VI. THE SUCCESSORS OF VESALIUS . . -37

VII. HARVEY ....... 42

VIII. AN EPITOME AND ESTIMATE OF HARVEY'S WORK 50

IX. THE DISCOVERY OF THE CAPILLARIES AND BLOOD

CORPUSCLES . . . . .69

BIBLIOGRAPHY ...... 77

INDEX ....... 79

75338

vu

LIST OF ILLUSTRATIONS

PLATE FACING PAGE

I. DIAGRAM OF THE CIRCULATION OF THE BLOOD . 8
II. DIAGRAM OF GALEN'S PHYSIOLOGICAL SYSTEM . 9

III. LEONARDO. By Himself . . . . .22

From a drawing in the Royal Library at Turin.

DRAWING OF THE HEART. By LEONARDO . . 22

From a drawing in the Royal Library at Windsor.

IV. VESALIUS . . . . . . .23

From the first edition of his Fabric of the Human Body.
Basel, 1543.

SERVETUS IN PRISON . . . . .23

From the statue by CLOTHILDE ROCHE at Annemasse, Haute-
Savoie, France (four miles from Geneva).

V. WILLIAM HARVEY . . . . . .42

From the painting by CORNELIUS JANSSEN in the Royal
College of Physicians (by courtesy of Sir D'ARCY POWER).

VI THE OLD LECTURE ROOM AT PADUA . . .43

(By courtesy of Professor CESARE FOLIGNO. )
HARVEY'S LECTURE NOTES (folio 80 verso) . . 43

From the MS. in the Royal College of Physicians.

ix

x LIST OF ILLUSTRATIONS

PLATE FACING PAGE

VII. FIGS. 1-4. EXPERIMENTS ON THE BANDAGED ARM. 68

From Harvey's work on the circulation, printed in Frankfort
in 1628.

FIG. 5. DISSECTION OF VEIN IN THIGH AND LEG . 68

From the work On the Valves of the Veins, by FABRICIUS,
printed in Padua, 1603.

VIII. FIG. i. LUNGS OF FROG, SHOWING CAPILLARIES . 69

From MALPIGHI'S work On the Lungs. Bologna, 1661.

FIG. 2. CAPILLARIES IN THE TAIL OF AN EEL . 69

From a letter by LEEUWENHOEK, dated Delft, 1698.

FIG. 3. RED BLOOD CORPUSCLES OF SALMON . 69

From a letter by LEEUWENHOEK, dated Delft, 1700.

FIGS. 4 AND 5. HUMAN RED BLOOD CORPUSCLES . 69

From the same letter as Fig. 3.

FIG. 6. HUMAN RED BLOOD CORPUSCLES DRAWN
FROM THE OBJECT UNDER A MODERN
MICROSCOPE . . . . .69

THE DISCOVERY OF THE
CIRCULATION OF THE BLOOD

THE CIRCULATION OF THE BLOOD

IF you place the finger of one hand lightly on the outer
side of the front part of your other wrist you will feel
a throbbing. This throbbing is called the pulse, and
has been known and observed by medical men for
thousands of years. The throbbing or pulsation is
caused by the expansion of a tube or blood-vessel of a
special type known as an artery. The expansion of
the artery at each pulsation or beat of the pulse is caused
by blood being forced into the artery by the special pump
known as the heart.

From the heart arises a great artery, the aorta, into
which the blood is pumped. The aorta is provided with
valves at the point at which it arises from the heart.
These valves are so arranged that they prevent any return
of blood to the heart. The blood, therefore, when once
forced into the aorta can move in one direction only,
namely, away from the heart.

Now the aorta has many branches and, as the blood
moves away from the heart, it enters them. These
branches in their turn have yet smaller branches. The
arteries go on branching until they get so small that they
cannot be seen except with a microscope. Through all

2 CIRCULATION OF THE BLOOD

this system of arteries the blood can move in only one
direction, always away from the heart.

At length, however, the arteries that we are tracing
cease to get smaller. Instead of branching and getting
smaller they now remain the same size and unite into a
network of minute tubes. Nearly every part of the body
is traversed by this network of tubes containing blood.
They are known as the capillary blood-vessels.

The pressure of the blood in the arteries rises with
each beat of the heart. As the pressure is raised, the
blood, as we have seen, is forced from the heart into
the aorta and onward into the other arteries. The blood
moves along them and escapes into the capillaries. The
effect of this escape is that the pressure in the arteries
falls, until it is raised again by the next beat of the heart
-and so on. If, therefore, an artery is cut or opened,
the blood will escape from it in spurts, each spurt corre-
sponding to a beat of the heart or a pulsation of the artery.

In the capillaries, owing to the extent of their network,
owing to the great amount of friction due to the minute-
ness of the vessels, and owing also to certain other factors
that we need not discuss here, the pressure of the blood
is much more steady than in the arteries, and does not,
as in the case of the arteries, increase and decrease in
spurts. The general movement of the blood in the
capillaries nevertheless continues. If you prick or cut
your finger you will not usually sever an artery, but only
capillaries. The result is that the blood flows from the
prick with a steady ooze, and does not come out in jerks
or spurts as in the case of a cut artery.

If the movement of the blood, passing always farther
and farther from the heart, is traced on and on, we find
that the network of minute capillaries at last unites again
into larger vessels. These vessels are called veins. The
veins in certain respects resemble, and in certain respects

CIRCULATION OF THE BLOOD 3

differ from, the arteries. They resemble the arteries in
conveying the blood and in having muscular walls.
They also resemble the arteries in their general dis-
tribution, for most arteries have a vein accompanying
them. One difference between the veins and the arteries
is that the veins tend to be larger. Moreover, the veins
have much thinner and less muscular walls. They
are therefore less distended by the blood that enters them
from the capillaries than are the arteries by the blood that
enters from the heart. As a result, the pressure in the
veins is lower than in the arteries or even than in the
capillaries. Blood, therefore, normally flows from the
capillaries into the veins.

If the veins into which we have traced the capillaries
be followed farther, we should find that they join or unite
into larger veins. These larger veins in their turn join
still larger veins. Finally, we should trace the veins to
one very large vein, the so-called vena cava, which enters
the heart.

We may now consider certain other differences between
the arteries and veins. Firstly, we may note that the
veins differ from the arteries in that they are equipped
here and there, at irregular intervals throughout their
course, with valves (Plate VII. Fig. 5). We have already
seen that where the aorta arises from the heart there is a
set of valves which prevents the blood from returning
to the heart. Somewhat similar though less efficient
valves are scattered through the course of the veins.
The cusps of these valves in the veins are so arranged
that they direct the flow of blood away from the capillaries
and towards the heart.

Another and very important difference between arteries
and veins is in the character of the blood that they con-
tain. The blood in the arteries is bright red, and that
in the veins is dark red. Blood enters the capillaries

4 CIRCULATION OF THE BLOOD

from the arteries a bright red colour. This colour
changes while in the capillaries and the blood that leaves
the capillaries and enters the veins is of a dark red colour.
The presence of bright red blood in a vessel is therefore
an indication that the blood is on its way from the heart
and that the vessel is an artery. The presence of dark
red blood in a vessel, on the other hand, is an indication
that the blood is on its way to the heart and that the
vessel is a vein. This fact gives rise to a simple rule for
stopping the bleeding of wounds. If the bleeding is
bright red it can be stopped by applying pressure above
the wound, i.e. on the heart side. If the bleeding is
dark red it can be stopped by applying pressure on the
side of the wound away from the heart.

There is one organ in which the relation that we have
described between bright red blood and dark red blood
is reversed. That organ is the lung. The blood which
goes from the heart to the lung is dark red, and the
blood which comes from the lung to the heart is light
red. We shall speak of the movement of the blood in
the lung later.

Let us recapitulate. If we were to follow any particle
of blood on its journey from the heart, we should find
that the arteries through which it passes become smaller
and smaller until the capillaries are reached. Then after
passing through the capillary network, our particle of
blood enters a vein from which it passes into larger and
larger veins, until it finally reaches the heart again.

The heart is really a hollow muscle which acts like a
pump. By contracting, as we have seen, it forces blood
from its cavities into the arteries. The heart contains
several cavities, but the cavity to which our particle of
blood has returned is not, in fact, the same as that from
which it started. To reach the cavity from which it
started, the particle has to make yet another journey.

CIRCULATION OF THE BLOOD 5

This time its course must be through one particular
and designated organ, the lung. In this second journey
our particle of blood again passes through an artery
which divides up, becoming smaller and smaller as it
does so. The division takes place on this occasion in
the lung. At last, still in the lung, a capillary network
is again reached. Passing through these capillaries
the particle goes on until it reaches again a small vein
which passes into a larger and larger vein. Through
these the particle goes on until it reaches the heart once
more. Finally it arrives at the actual cavity of the heart
from which it started.

To get back to its starting-point, our particle of blood
has thus to go through the journey, heart-cavity, artery,
capillary network, vein, at least twice. There are thus
two main capillary circulations. One of them passes
through the lung, and is called the pulmonary or lesser
circulation. The vessels of the other capillary circula-
tion, which we began by describing in greater detail,
penetrate almost every part of the body, and this
circulation is spoken of as the systemic or greater
circulation.

Each of these is spoken of as a circulation, not because
the movement is actually in a geometrical circle, or any
figure resembling a circle, but because a circle is a figure
that ends at the point at which it started. You must
nevertheless remember that the word circulation should
not, in absolute strictness, be applied to either of these
by itself, since a particle of blood cannot get back to the
actual cavity of the heart from which it started unless it
passes through both circulations. There are thus, strictly
speaking, not two circulations, but only one circulation.

Let us now turn to examine the different parts of
the circulation somewhat more minutely, beginning with
the heart itself. The heart is a very complicated structure.

6 CIRCULATION OF THE BLOOD

The difficulty of understanding it is largely due to the
fact that the cavities which it contains are, as it were,
twisted on one another in an irregular fashion and in
three dimensions. It will be much easier to understand
if we imagine it straightened out on a flat surface with
its cavities exposed (Plate I.).

The heart contains four cavities, two on each side.
The two cavities on the same side are in direct com-
munication with one another, so that blood passes freely
on each side from the upper cavity or auricle to the lower
cavity or ventricle of the same side. It is important to
remember that there is no communication between the
auricle and ventricle of one side of the heart and the
auricle and ventricle of the other side of the heart, except
through the blood-vessels and capillaries. The exist-
ence of a more direct means of communication was firmly
believed until the seventeenth century. This belief, as
we shall see, was a very great obstacle to the advance of
physiological knowledge. The removal of this belief
was one of the most important events in the history of
science.

From each of the two ventricles arises a great artery
through which the blood is distributed. On the other
hand blood is brought to each ventricle from its corre-
sponding auricle, which in its turn receives it from a
corresponding great vein. The direction of the move-
ment of the blood is determined by a series of valves.
Valves are placed between auricles and ventricles on
both sides, and there are other valves at the entrance of
the great arteries that arise from each of the two ventricles.

When the right ventricle contracts, blood is driven
into a great artery that resembles the aorta in certain
respects, and differs in others. This great artery is
known as the pulmonary artery. It resembles the aorta
in its muscular character, in size of its cross-section and

CIRCULATION OF THE BLOOD 7

in the possession of valves at its commencement, which
prevent the movement of blood except away from the
heart. It differs from the aorta in being much shorter
and breaking up much sooner into branches, though
these facts cannot be brought out in a diagram. It also
differs from the aorta in supplying branches only to the
lung instead of to all parts of the body.

In the lung the branches of the pulmonary artery, like
the branches of the aorta, break up, as we have seen,
into a capillary network. The pulmonary capillary
network, again like the systemic capillary network, passes
into veins. These veins in the lung unite and become
larger and larger until they all end in a great trunk, the
pulmonary vein, which opens into the right auricle.

We have compared the pulmonary artery to the aorta,
and referred also to certain points of difference. There
is, however, one great difference between the pulmonary
artery and the aorta that was a very great puzzle to the
ancient physiologists. The nature of that difference is,
however, quite clear nowadays. The pulmonary artery
contains dark red blood, the aorta contains light red
blood. This fact is easily understood if we examine
how the blood reaches these two great vessels. We
have already seen blood changed from light to dark in
the systemic capillaries, and passing from them into
the veins, thence into the vena cava, thence into the
right auricle, thence into the right ventricle, and thence
into the pulmonary artery. The pulmonary artery
branches and breaks up into capillaries in the substance
of the lung. In these pulmonary capillaries the change
that took place in the systemic capillaries is reversed.
Dark red blood enters the pulmonary capillaries and it
emerges from them light red. From the pulmonary
capillaries this light red blood passes into the pulmonary
vein. The pulmonary vein conveys it to the left auricle,

8 CIRCULATION OF THE BLOOD

whence it passes to the left ventricle and from thence
the light red blood is forced into the aorta and systemic
circulation.

These alterations of colour from light to dark and from
dark to light are indications of chemical changes. They
are due to the chemical combination of the red substance
of the blood with oxygen in the case of the light blood,
and with carbon dioxide in the case of the dark blood.
The nature and meaning of this change will be discussed
in a companion volume of this series dealing with respira-
tion. In this book we shall only consider the movement
of the blood from a mechanical point of view.

Let us now again trace a particle of blood on its journey.
This time we can follow it through the entire circulation.
Leaving the left ventricle, when the walls of that cavity
contract, the particle is forced through the valves into
the great artery known as the aorta. From the aorta it
passes into smaller and ever smaller arteries, finally
reaching the systemic capillary network. After travelling
through that network it enters a vein. Thence it passes
into larger and ever larger veins, until it ultimately enters
the great vein known as the vena cava that opens into
the right auricle. It has now completed the systemic
circulation. As the right auricle contracts, our particle
of blood passes through the valves between the right
auricle and right ventricle into the right ventricle. From
there it passes into the great pulmonary artery, which
conducts it to the lung. In the lung the pulmonary
artery breaks up into branches and finally into capillaries.
Through these our particle travels until it reaches a
tributary of the pulmonary vein and finally the pulmonary
vein itself. The pulmonary vein empties its blood into
the left auricle, carrying our particle with it. From the
left auricle the particle of blood passes at last into the
left ventricle, from which it started.

PLATE I

RIGHT* LEFT
AUR. \AUR.

^^°rais^

DIAGRAM OF THE CIRCULATION OF THE BLOOD.

PLATE II

L I V £
NATURAL SPIR

DIAGRAM OF GALEN'S PHYSIOLOGICAL SYSTEM.

CIRCULATION OF THE BLOOD 9

This is only a very rough description of the circulation
of the blood. It leaves out of account some very im-
portant factors, such, for instance, as the movements of
the chest wall during breathing, and in general the effect
of respiration on the circulation. It leaves out of account
also the fact, which may be gathered from the diagram
(Plate I.), that the veins from certain organs, as, for
example, the intestine, break up into capillaries for a
second time before returning to the heart. Bearing these
omissions in mind, however, we may turn to a discussion
of the process by which it was discovered. This discovery
was the work of an Englishman, William Harvey. Before
we can understand his work we must learn something of
what men believed before his time concerning the action
of the heart and blood-vessels.

II

THE KNOWLEDGE OF THE VASCULAR SYSTEM

IN ANTIQUITY

THE pulse is the most obvious activity of the circulatory
or, as we may call it, the vascular system. Even in very
ancient times physicians had noted its existence and
observed its variations. Thus in an Egyptian medical
papyrus, written about 1500 B.C., the pulse is mentioned,
and we learn that its character and force, size and fre-
quency, were even then considered to give an indication
as to the state of a patient's health. The Egyptian
papyrus considers that the pulse is related to the blood-
vessels.

Outside Egypt also physicians attached great im-
portance to the pulse. In the writings of the Asiatic
Greek physician, Hippocrates of Cos, who lived about
400 B.C., we find that the pulse is considered to be due to
movements of blood-vessels, and that these have been
traced to the heart. As the pulse was even then con-
stantly being examined by medical men, this view made
them take much interest in the heart and blood-vessels.
Physiological systems were therefore very early drawn
up, based on the relationship of the heart and vessels
to the pulse.

The best known of these systems is that of the Greek
philosopher and naturalist, Aristotle, who taught at
Athens, and died in the year 322 B.C. Aristotle was one
of the best observers of nature that have ever lived, but

IO

KNOWLEDGE IN ANCIENT TIMES n

he made some unfortunate mistakes concerning the
vascular system. Thus he attached enormous and ex-
aggerated importance to the heart. Not only did he and
his successors rightly regard it as the centre of the vascular
system, but they also attributed to it various other
qualities and functions that we now know it does not
possess. They regarded the heart as the seat of the in-
telligence and the source of the bodily heat. Moreover,
they considered that, during the process of development,
the heart was the first organ to develop, while at death
it was the last organ to show activity. These views have
since been shown to be erroneous.

Soon after the time of Aristotle, and about 300 B.C.,
a great medical school was founded at Alexandria in
Egypt. That country had been conquered by Alex-
ander the Great, after whom the town Alexandria was
named. On Alexander's death, Egypt came under the
rule of one of his generals, Ptolemy, who founded a
dynasty which became extinct in the time of Julius Caesar
with the famous Queen Cleopatra, just before the
Christian era.

The town of Alexandria, though in Egypt, was a
favourite residence of this Greek dynasty, and became
more Greek than Egyptian. Ptolemy and his successors
were disposed to encourage learning, and at the medical
school at Alexandria very remarkable physiological re-
searches were made. These were entirely the work of
Greek physicians, and by them the knowledge of the
heart and the vascular system was placed on a more
scientific basis. Thus there arose in Alexandria a tradi-
tion of physiological learning and research that was to be
found nowhere else in the ancient world.

About the middle of the second century A.D. there came
as a student to the still flourishing medical school at
Alexandria a young Asiatic Greek, whose views were

12 CIRCULATION OF THE BLOOD

destined to exercise the most profound influence on the
course of science. His name was Galen, and he became
one of the most eminent exponents of science in all
antiquity. Galen afterwards practised for many years
at Rome, and became the medical attendant to the
Roman Emperor, Marcus Aurelius. He died in the year
200 A.D. His account of the vascular system is of great
importance for our subject.

Galen's views on the nature and action of the heart,
the blood-vessels, and the pulse remained current for
some fifteen hundred years, and all references to the
nature and action of the heart, the blood, or the pulse
in older English writers — for example, in Chaucer or
Shakespeare — can be traced to interpretations of Galen's
works. The ideas of Galen are therefore of more than
historical interest. An understanding of them is neces-
sary not only for the history of science, but also for
the explanation of many allusions in literature and not
a few colloquial expressions. We shall therefore turn
at once to a discussion of Galen's physiological views.

Galen taught (Plate II.) that the body was governed by
three principal structures that formed a sort of aris-
tocracy among the organs of the body ; these were the
liver, the heart, and the brain. Ingested food passed
into the intestines and was absorbed from there as
chyle, and carried by the portal vessel to the liver. In
the liver this chyle was elaborated into blood, and
charged with an imaginary essence, the natural spirits.
The presence of these imaginary natural spirits was
supposed to be necessary for the continuance of even
the lowest form of life.

The natural spirits were distributed from the liver to
the various parts of the body, and they were sent thither
by means of the veins. The liver was thus regarded by
Galen as the centre of the venous system. The veins

KNOWLEDGE IN ANCIENT TIMES 13

sent blood charged with nourishment, absorbed from the
intestines, together with natural spirits absorbed from
the liver, to all parts of the body. In the veins this
nutritive blood was thought to ebb and flow, up and down.
During this ebb and flow, the veins absorbed into their
blood impurities from all parts of the body. No idea of
circulation was involved. A large branch of the venous
system entered the right ventricle.

Two parts of this venous system are of special
interest to us for the understanding of Galen's ideas.
One was the vessel that he called the arterial vein
which goes to the lung. It is the structure we now call
the pulmonary artery. This vessel when it reached the
lung discharged, as he thought, all the impurities that
had been brought by the venous system from the various
parts of the body. The impurities passed into the air-
tubes of the lung, and were thence exhaled into the outer
air. Galen knew that animals could not live indefinitely
in a closed space, and died if so confined. This event
was thought by him to be due to the impure and poisonous
substances conveyed by the breath to the air.

The second branch or rather series of branches of
Galen's venous system that are of special interest for our
purpose had no real existence. They were entirely a
product of Galen's imagination. Their existence, how-
ever, was firmly believed for many centuries, and this
belief was one of the main obstacles to the true explana-
tion of the action of the heart. Galen thought that some
of the blood which entered the right ventricle passed
through the muscular wall or septum that lies between the
two ventricles, and so reached the left side of the heart.
Now it happens that on the walls of the septum which
face the cavity of the two ventricles are a large number of
blind pits. It was believed that these pits represented a
series of minute passages from one ventricle of the heart

14 CIRCULATION OF THE BLOOD

to the other. Although a seeker, or even a fine bristle,
cannot be made to penetrate from one ventricle to the
other through any of these pits, yet for ages, and in spite
of the evidence of their senses, men continued to believe
that these channels really existed. The great Galen had
believed in their existence, and that was enough ! If they
could not be found, it was thought that it was because
they were so small that they were beyond the reach of
vision. Their existence was necessary to explain the
nature of the heart's action. It must be remembered
that there were then no microscopes or lenses to increase
the power of vision, so that it was the easier to believe in
the existence of these channels. Furthermore, no better
explanation of the physiology of the heart than that
provided by Galen was forthcoming for very many
centuries.

We have now to consider what Galen and his followers
believed to be the fate of the small amount of blood that
made its way, as they thought, drop by drop, through
this septum by means of the imaginary passages. Galen
knew well of the difference in appearance between
arterial and venous blood, he fully recognised the light
colour of the blood in the arteries as compared with the
dark colour of the venous fluid. Though he had no clear
idea of the nature of respiration, though he knew nothing
about the composition of the atmosphere, and though
oxygen had not yet been discovered, yet he attributed
this difference between the arterial and venous blood to
a cause not very different from that assigned to it to-day.
He considered it was the action of the air that produced
the lighter colour of the arterial blood.

Galen knew too of the existence of the important
vessel that empties itself into the left auricle which we
call the pulmonary vein, but which he called the venal
artery. We know now that this vessel brings oxygenated

KNOWLEDGE IN ANCIENT TIMES 15

blood to the heart, and he knew that it carried something
to the heart and had an important part to play in altering
the character of the blood. He seems to have believed,
however, that it did not bring aerated blood to the heart
but air only, and that this air it drew from the cavities
of the lung. He regarded this vessel as a branch of the
arterial system, and it was on this account, recognising
the thin and vein-like character of its walls, that he called
it the venal artery. Galen paid very little attention to
the auricles, regarding them merely as dilatations at the
entry of the great veins into the heart. He therefore
described the heart as having only two cavities, the
two ventricles. The air carried by this pulmonary vein,
or venal artery, as he called it, entered, Galen thought,
the cavity of the left ventricle. There it met writh the
trickle of blood that came through the supposed channels
in the septum, and by its combination with this trickle
of blood of venous origin he believed that arterial blood
was produced. An important feature of the arterial
blood was the presence in it of a second kind of spirits,
the so-called vital spirits. These spirits, derived from
the heart, differed from the natural spirits derived from
the liver. The vital spirits were responsible for all kinds
of movement and muscular activity. Arterial blood
carrying its charge of vital spirits was distributed by
the arteries to all parts of the body.

We need not, for our purposes, follow it there, but
we may glance for a moment at one group of arterial
branches that Galen considered were of special interest.
Some of the arterial blood naturally reached the brain,
where, according to Galen, it was charged with a third
kind of spirits, the animal spirits. These animal spirits,
like the other forms of spirits, Galen believed to be also
distributed to different parts of the body. The animal
spirits, however, were, it was thought, separated from the

16 CIRCULATION OF THE BLOOD

blood, and sent out to the body as a sort of nervous
fluid. The distribution of this imaginary fluid took
place through the nerves, which were regarded as hollow.
The animal spirits were held responsible for all the kinds
of activity that we call nervous.

To return to the blood itself we may emphasise that
Galen's view of the action of air on the blood was not
wholly imaginary. It was grounded on observation in
so far as it took account, firstly, of the necessity of air
for life ; secondly, of a real difference between venous
and arterial blood ; thirdly, of the fact that the systems
in which both kinds of blood, arterial and venous, are
contained have direct connection with the heart ; and
fourthly, of some relation to the warmth of the body,
the supposed nature of which we must now consider.

Long before Galen's time physicians had come to
associate heat with life. They had observed that animals
grew cold when dead, while living animals remained
warm without the aid of any apparent fire. They thus
thought that the animal heat produced without fire was
a special property of living matter and was different from
the heat that was derived from fire. It was therefore
given a special name and called the innate heat. The
innate heat was held to be developed specially by the
heart, an organ on which, as we have seen, great stress
had been laid by Aristotle, who lived five hundred years
before Galen. The name of the great naturalist, Aristotle,
thus became connected, in the minds of later writers,
with the idea of this mysterious innate heat. The con-
nection of so important a name as that of Aristotle with
this idea had very important effects in a later age.

Galen, however, was dissatisfied with the current
view of the innate heat. He refused to accept its peculiar
and inexplicable nature, and he sought to explain it
and to bring it within his physiological system. He

KNOWLEDGE IN ANCIENT TIMES 17

ventured to compare the action of the heart to that of
a fire or furnace. The air taken to the heart by means
of the venal artery (our pulmonary vein) was combined,
as he thought, with the blood in the left ventricle to
form the animal spirits that were, in his view, such an
important feature of the arterial blood. In the process
something akin to combustion took place, and heat —
the animal heat that was the sign of life — was given off.
This made the heart the hottest organ of the body. Its
heat was, however, regulated and controlled, as he thought,
by the very agent that fed it. The mechanism for this
regulation and control was placed by Galen in the lung.
Air entering the lung kept that organ, it was thought,
at a low temperature, the superfluous heat being got rid
of by the warm breath. The lung was thus enabled to
act as a sort of cooling bath to the heart. Respiration, in
the Galenic view, thus became a mechanism for regulat-
ing the heat of that furnace, the heart. If too little
air were taken in, the furnace might be damped down
and even put out. If too much air were taken in, the
flame was fanned, combustion became fiercer, and the
heat increased as in fever. If a great deal too much
was taken in, the furnace might be blown out as effec-
tively as it might be suffocated by too little air.

Ill

THE REVIVAL OF LEARNING

DURING the Middle Ages the beliefs about physiology
were always based on Galen. They were frequently
confused and often the result of a misunderstanding
of his work. In the fifteenth century, however, took
place the so-called Renaissance or Revival of Learning.
Greek works began to be recovered and to be more
accurately studied. The first step towards any improve-
ment on the views of Galen was naturally a proper under-
standing of what he really said. For that purpose a
correct knowledge of Greek was needed, and such a
knowledge had been exceedingly rare in the Middle
Ages. In the fifteenth century, however, knowledge of
this kind became more common. It was an age of
enthusiasm for the Classics and of revival of classical
scholarship. Accurate translations of the Greek works
of Galen were made. The printing-press was invented
about the middle of the fifteenth century, and towards
its end printed copies of the new translations of the
works of Galen began to be distributed all over Europe.
So it came about that the Revival of Learning was coin-
cident with a Revival of Science.

An indication of this scientific revival was a new
interest in dissecting. Even during the Middle Ages
there had been a certain amount of dissection in con-
nection with medical courses at the Universities. At
first this dissection was undertaken merely with the

18

THE REVIVAL OF LEARNING 19

object of verifying Galen's views. The professor read
out the text of Galen, and the students looked on the
dissections as merely a method of making it rather easier
to remember what Galen had said. The dissection, in
fact, was supposed to illustrate Galen, rather than
Galen to explain the dissection. It was nearly the
middle of the sixteenth century before there was any
real and open discussion of Galen's views in the
Universities.

But there were also other influences at work. Along
with this Revival of Learning and Revival of Science
there was also a Revival of Art. Every one has heard of
the names of some of the great artists of the Renaissance
— Michelangelo and Raphael for instance. These
artists, and many like them, began to study the human
form very closely. They soon found that to represent
it accurately some knowledge of anatomy, and especially
of the bones and muscles, was needed. The artists,
therefore, also began to dissect.

Now among these great artists were some who took
more than a purely artistic interest in the structure and
functions of the parts of the body. The best known of
these, and the most interesting for our purposes, was
Leonardo da Vinci, who lived from 1452 to 1518. Like
most of the great artists and scientists of the period he
lived in northern Italy. His work was done chiefly at
Florence and Milan. Leonardo was an artist, but he was
also a great deal more. He was a man of enormously
powerful and inquiring mind, and his achievements in
Science are at least as remarkable as his eminence in Art.
He had determined to write a text-book of anatomy and
physiology. Though he did not live to publish it, some
of his beautifully illustrated notebooks on these subjects
have survived. They enable us to form an idea of what
a magnificent work it would have been. We shall here

20 CIRCULATION OF THE BLOOD

consider some of his researches which bear upon the
heart and the organs of respiration.

Leonardo was the first man to question the views of
Galen. He made most careful first-hand investigations
on the bodies of men and animals, and he performed
many physiological experiments. It happened that he
was particularly interested in the heart and vascular
system. In the course of his researches he came to the
correct conclusion that the branches of the air-tubes in
the lungs, the bronchi, as we call them, branch and gradually
diminish in size and finally end blindly. He inflated the
lungs with air, and found that whatever force he used,
he was unable to drive the air from the bronchi into
the heart. He therefore inferred quite correctly that
Galen's venal artery (our pulmonary vein) did not convey
air to the heart as the followers of Galen believed that
it did.

Leonardo then turned to the examination of the heart
itself. First he examined its structure and form, and pre-
pared more accurate drawings of it than had been made
by any before him (Plate III.). Then he made sections
and dissections of it, and examined its valves. He observed
and carefully figured the four cavities of the heart — the
two ventricles and the two auricles. Galen had known
the ventricles, and had attached much importance to them ;
the auricles, as we have seen, had been almost entirely
neglected by him, as he considered that their only function
was to prevent over-distension of the ventricles. Galen
thus described the heart as having only two cavities.
Leonardo correctly described it as having four.

Of all the bodily movements, Leonardo evidently found
those of the heart and vascular system at once the most
perplexing and the most absorbing. To the question of
their nature he returned again and again, expending on it
much of his time, his art of dissection, his keen observa-

THE REVIVAL OF LEARNING 21

tion, and his knowledge of the laws of physics. His
drawings, experiments, and deliberations tell their tale of
his unceasing efforts to reach a solution of this abstruse
problem. Leonardo ultimately succeeded in grasping
quite clearly the nature and action of the valves at the
root of the great arteries, and he verified his views by
most remarkable experiments. He proved conclusively
that the valves allowed the blood to pass in only one
direction, and prevented its regurgitation.

Leonardo, however, gave no complete or clear descrip-
tion of the vascular system as a whole. He was not able
entirely to emancipate himself from the old idea of the
passage of the blood from the right ventricle through the
septum into the left ventricle, although he sometimes
seems doubtful about the truth of it, for he emphasises the
fact that the pores in the septum are invisible. One
must remember, however, that Leonardo has not left us
any systematic account of the subject ; his remarks are
distributed over many years and many manuscripts.
Nor is it surprising that Leonardo, who was no physician,
should be incomplete and obscure in dealing with one of
the most difficult physiological problems. It is also to be
remembered that Leonardo did not publish the results
of his research — it is only comparatively recently that
they have been found in his manuscripts.

But although Leonardo's works remained in manu-
script, it must not be assumed that he did not influence
his contemporaries and successors. At any rate, soon
after his time it is evident that the questions that he
had raised concerning the heart and blood-vessels were
attracting others, and were generally regarded as an
important problem needing solution. This in itself
shows that men were beginning to doubt the basis of the
current physiological views which were still those of
Galen. Thus Jacob Berengar of Carpi, who died twelve

22 CIRCULATION OF THE BLOOD

years after Leonardo, and who, like him, worked in
northern Italy, was at work on the same topic. He, too,
was carefully investigating the valves of the heart, and
was greatly puzzled as to their action. He saw that they
would admit blood only in one direction, but he also
failed to carry the matter further.

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IV
VESALIUS AND THE NEW ANATOMY

A MORE important writer than Berengar and one of the
greatest scientific investigators that has ever lived was
the Belgian, Andreas Vesalius, who was beginning his
work about the date of Berengar's death. Vesalius was
born at Brussels on the last hour of the last day of
the year 1514. Even as a boy he showed very great
interest in science. He was always observing nature
and constantly dissecting the bodies of any animals
that he could get. A taste for natural history is common
enough among boys and girls nowadays, but it was much
rarer then. Nowadays nature study is taught in many
schools, and it is easy to get books to help one. In his
day men were but just emerging from the Middle Ages,
when the study of nature was little thought of and no
such books had yet been written. Vesalius had there-
fore to find his own way. For such a boy there was
then only one profession possible, that of medicine.

Vesalius therefore became a medical student, and he
studied first at the University of Louvain and afterwards
at Paris. We have already seen how anatomy was taught
in mediaeval times, and the methods of instruction at
Louvain and Paris had not improved much, if at all, on
those of the Middle Ages. Vesalius soon got tired of
hearing long passages of Galen read out by the professor.
He therefore determined to go to northern Italy, where
the newer and more scientific methods were being

24 CIRCULATION OF THE BLOOD

practised. Padua was the university of his choice. He
immediately made his mark there, and was appointed
a professor when only twenty- four years of age. He
established a scientific tradition at Padua which that
university has retained to this day.

It may seem surprising that a Belgian should be
appointed to teach in an Italian university. You must,
however, remember that at that time there was only one
language for learning — Latin. All learned books, all
medical books, nearly all religious books, all books on
history and biography, and even most school text-books,
in fact all serious books of any kind were at that time
written in Latin. The lectures in the universities and
even most of the lessons in the schools were given in
Latin. The native language of a professor was there-
fore" not of great importance. The really important
thing was that he should be able to speak and write
Latin fluently. This was, therefore, an essential accom-
plishment of every educated man, and one which Vesalius
had early acquired.

No sooner was Vesalius settled as a professor at Padua
than he applied himself with extraordinary diligence to
lecturing and to research. He was a most successful
teacher, and students crowded to hear him. His audience
is said to have frequently numbered as many as five
hundred. As an aid to his pupils he issued, in 1538,
soon after his appointment, a sort of students' guide
to anatomy and physiology. It consisted of six fine
plates of pictures with very full descriptions. These
pictures show that he had made a careful examination
of the human skeleton, but that his physiological views
were still taken from Galen and Aristotle. In these
plates he still speaks, for instance, of the liver as the
source of the veins, and the heart as the source of the
arteries and of the innate heat.

VESALIUS AND THE NEW ANATOMY 25

During the four years that followed the issue of this
guide he had ample opportunities to dissect. He spent
all the time he could spare from teaching in the prepara-
tion of his great work on anatomy and physiology. It
was printed in 1543 in a magnificent and beautifully
illustrated large folio volume under the title The Fabric
of the Human Body. This work is one of the landmarks
in the history of science. The Fabric of the Human
Body is the first great work of anatomy or physiology
since the time of Galen. It is, for its time, a wonder-
fully full record of a prodigious number of accurately
recorded discoveries and investigations made by a single
observer.

After the issue of his students' guide of 1538, Vesalius
had found that Galen and Aristotle were by no means
always to be trusted. This discovery led him to doubt
constantly any statement of Galen or Aristotle. His
scepticism was sometimes excessive, for Galen and
Aristotle were excellent observers. These doubts, how-
ever, led Vesalius to put every statement made by his
predecessors to the actual test of experience, and this
gave his work an epoch-making value.

When Vesalius came to investigate the heart he was
in a peculiar difficulty. All the physiology of his time
was based on the view of Galen, which necessitated a
belief in the passage of blood from the right ventricle
to the left through the pores of the septum and a belief
that air entered the heart through the venal artery (our
pulmonary vein). To cast doubts on this without ex-
plaining the action of the heart would be to upset the
whole of the current notions of the workings of the human
body without putting anything in its place. This
Vesalius hesitated to do, and, although he hinted in his
book that the passages through the septum have no real
existence, yet he did not at first say so outright.

26 CIRCULATION OF THE BLOOD

The work of Vesalius on The Fabric of the Human
Body was very well received by the scientific world.
It immediately became the recognised text-book. Like
all such works, it was inevitably given the most sincere
form of flattery — it was copied by inferior writers, who
often treated the discoveries of Vesalius as though they
were their own. It is very remarkable that in spite of
this flattering reception Vesalius was by no means satis-
fied with his position as a professor. It is believed
that he was unduly sensitive to the criticism that was
not unnaturally made of a work which had caused such
a big stir in the scientific world. Perhaps, too, he felt
unable to continue his work longer without expressing
more clearly his disagreement with current views. Yet
he really had no physiological theories to offer in place
of those of Galen, and to destroy Galen's views without
having anything to put in their place would be simply
to introduce confusion. Perhaps, too, he feared the
criticism of the theologians. Galen and Aristotle had
been so long looked on as infallible that their views
had become interwoven with the religious opinions of
the age, which was a very intolerant one. These views,
Vesalius well knew, it would be dangerous to disturb.

Whatever the reasons may have been, soon after the
publication of his great work Vesalius took an extreme
step. He resigned his professorship, burnt his notes and
papers, and took up the post that was offered him as
physician to the Emperor Charles v., the greatest monarch
of the age. Vesalius was then only twenty- nine years
old, but his scientific career was closed. Nevertheless,
his book had sold so well that the edition was soon
exhausted. The demand for more copies could only be
met by imitations of his work by other hands. At last
in 1555, twelve years after the appearance of the first
edition, he was prevailed on to issue a second.

VESALIUS AND THE NEW ANATOMY 27

Vesalius, fully occupied as court physician, was no longer
in a position to make new physiological or anatomical
observations. The second edition of the work, though
distinctly an improvement on the first, does not therefore
exhibit many facts that he had not already recorded. It
does, however, contain certain changes in point of view
that were very important for the subsequent development
of physiology. In the second edition of his great book
Vesalius no longer merely hints his doubts as to the
character of Galen's physiology, he openly asserts that
he is unable to verify its fundamental bases. He was
now in a strong position as the personal attendant of a
powerful and orthodox monarch. He could therefore
say what he meant with comparatively little fear or
risk.

We may take a single instance of this new outspoken-
ness. In his description of the septum of the heart he
had written in the first edition : The septum of the
ventricles is formed from the very densest substance of
the heart. It abounds on both sides with pits imprinted
on it, by reason of which it is provided with an uneven
surface towards the ventricles. Of these pits none, so
far as the senses can perceive, penetrate from the right
to the left ventricle. We are thus forced to wonder at
the art (industria) of the Creator by which the blood
passes from right to left ventricle through pores which
elude the sight." This passage is altered to something
quite different in the second edition, where he writes :
4 Although sometimes these pits are conspicuous, yet
none, so far as the senses can perceive, passes from the
right to the left ventricle. ... I have not come across even
the most hidden channels by which the septum of the
ventricles is pierced. Yet such channels are described
by teachers of anatomy who have absolutely decided that
blood is taken from the right to the left ventricle. I,

28 CIRCULATION OF THE BLOOD

however, am in great doubt as to the office of the heart
in this part."

He further sets forth his whole policy with reference to
Galen's view in the following interesting passage : ' In
considering the structure of the heart and the use of its
parts, I have brought my words for the most part into
agreement with the teachings of Galen : not because I
thought that these were on every point in harmony with
the truth, but because, in referring now and again to a new
use and purpose for the parts, I still distrust myself.
Not long ago I would not have dared to turn aside even a
nail's breadth from the opinion of Galen, the prince of
physicians. . . . But the septum of the heart is as thick,
dense, and compact as the rest of the heart. I do not,
therefore, know ... in what way even the smallest
particle can be transferred from the right to the left
ventricle through the substance of that septum. . . .
When these and other facts are considered, many points
concerning the arteries come forward about which doubts
may reasonably arise. We may note too that almost no
vein goes to ventricle, intestines, or spleen without an
accompanying artery, and likewise the portal vein has an
accompanying artery almost throughout its course."

ffi *e*

SERVETUS

THE next contribution to our knowledge of the circula-
tion comes from a most unexpected source. It is not
found in a scientific work but in a book on Theology.
The recurrence of the discussion in such a place suggests
how wide was the interest taken in the problem. The
author of this work was Michael Servetus. As his career
was one of the most remarkable and tragic in the whole
history of science, we shall say a few words about him.

Michael Servetus was born in 1511 at Tudela. That
town is situated in Navarre, a district in the north
of Spain, close to the French frontier. Servetus was
educated mainly in France, — first at Toulouse, where he
studied theology, and then at Paris, where he studied
medicine and law. It is interesting to learn that he had
there the same teachers as Vesalius. It is even possible
that the two were actually fellow-students.

After Servetus left Paris he led a somewhat wandering
life. At this time religious feeling ran very high in
France, and indeed throughout Europe. The religious
movement known as the Reformation was very recent
and was still in progress. There was much bitterness
between Catholics and Protestants, and neither party was
willing to spare the other or to have mercy on any within
their own body who was suspected of heretical views.
Servetus was an inveterate theological disputant, and he

wrote books that were most unwelcome to both parties.

39

30 CIRCULATION OF THE BLOOD

It is unnecessary for us to deal with his theological views,
but we may say that they approached the standpoint
nowadays called Unitarian. What concerns us is that
in one of his books, written in Latin, with the title The
Restitution of Christianity, he shows that he had attained
to a clear view of the nature of the lesser circulation.

It may be asked why Servetus, a theologian before
all things, took so much interest in physiology. The
question is not difficult to answer. He had a belief that
the study of physiology was one of the paths which lead
to a knowledge of God. To know the spirit of God he
considered that it was necessary to comprehend the spirit
of man, and to know the spirit of man he thought it was
necessary to attain to a right understanding of the
structure and workings of the body in which that spirit
dwells. On this account he introduced physiological
discussion into his theological works.

If one glances at the theological writings of Servetus, —
and there are few who now do this, — one sees at once that
he is an obstinate and persistent advocate of the absolutely
literal interpretation of Scripture. He accuses the world
in general, and the Protestant theologian Calvin in par-
ticular, of not understanding Biblical phraseology. He
piles up a host of quotations to show that he alone under-
stands it. To give an example which bears on our subject.
The Bible in several places closely associates blood with
life. This idea is perfectly natural. It was by no means
confined to the Bible, but was widely held in antiquity.
Servetus, however, seizes on several Biblical passages
which bring out this association. Thus in Genesis,
chap. ix. ver. 4, we read of " the life which is the blood " ; *
in Leviticus, chap. xvii. ver. 1 1 ,we read " the life of the flesh
is in the blood" ; and in Deuteronomy, chap. xii. ver. 23,

1 In the Latin " Vulgate " version in current use among Catholics
this passage is rendered differently.

SERVETUS 31

" the blood is the life." In the Latin translation of the Bible
which Serve tus used, the word life is represented by the
word anima, which may be translated spirit. These
passages all have their special contexts, which do not
concern us here. Nor did the contexts concern Servetus,
who was all for the most literal interpretation. " The
blood is the spirit," we can imagine Servetus saying,
' and if we would know how the spirit is formed we
must learn how the blood is formed, and if we would
know how the blood is formed we must know how it
moves." This is a point he discusses in the Restitution
of Christianity.

In his purely physiological ideas, as expressed in the
Restitution of Christianity, Servetus is still mainly under
the influence of Galen and Aristotle, though he allows
himself certain minor departures from their views. For
the most part, however, he is merely repeating their
phrases with his own theological tinge added. " There
are said to be in us," he tells us, " three kinds of spirits —
natural spirits, vital spirits, and animal spirits — but there
are, in fact, not three but only two kinds of spirits, for
the vital spirits are passed on from the arteries to the
veins, where they are called natural spirits. Thus first
we have the blood, the site of which is the liver and
veins. Then we have the vital spirits, the site of which
is the heart and arteries. Thirdly, we have the animal
spirits, the site of which is the brain and the nerves.
In all three we see the workings of the spirit of the one
living God. ... It was into the heart of Adam that God
first breathed the spirit [Genesis, chap. ii. ver. 7], and it
was afterwards that it passed to his liver. By inspiration
through mouth and nose, spirit is taken in, and that which
is inhaled goes to the heart. The heart is the first part to
live, and it is the central source of bodily heat. . . . But
the material in which the spirit is carried is the blood,

32 CIRCULATION OF THE BLOOD

which is derived from the liver. Hence the spirit is said
to be in the blood, or to be blood. The spirit is not said
to be in the chambers of the heart, nor yet in the mass of
the brain or liver, but in the blood itself, as God Himself
teaches in Genesis, chap. ix. [ver. 4] ; Leviticus, chap,
xvii. [ver. n] ; and Deuteronomy, chap. xii. [ver. 23]."

In all this there are only the doctrines of Galen and
Aristotle slightly altered by the theology of Servetus and
especially by his reading of the Bible. The one real
change that he has made is to do away with the natural
spirits, the product of the liver. He therefore admits
only one kind of spirits in the blood, whether arterial or
venous. This idea, it may be thought, would make it
necessary for him to emphasise the communications
between veins and arteries, because the vital spirit that
is formed in the heart, and especially in the left ventricle,
cannot get into the veins without such communication.

Now there is a passage in the writings of Galen in
which he speaks of anastomosis between the arteries and
veins. In older Greek the word anastomosis meant the
act of making a mouth or hole. In later writings, how-
ever, the word came to mean something rather different.
It might be used for two structures that are closely
intertwined or connected with each other as are the veins
and arteries, and Galen sometimes uses the word in this
latter sense. In the passage in question, however, he
has certainly the original meaning,1 and really seems
to imply that there are certain openings between the
arteries and the veins. He does not, however, attach
importance to these openings. They are not necessary
for his physiological system. Galen's actual phrase is
' throughout the body the arteries anastomose with the

1 De nsu partium, vi. § 10. The actual word he uses here is
<TvvavaaT6/j.ioi>Ta.i, which undoubtedly means that the vessels are joined
together by a mouth. A similar statement is made in vi. § 17.

SERVETUS 33

veins. They thus mutually give to each other blood and
spirit through certain invisible and extremely narrow
passages." The sentence presumably means that these
fine passages unite artery and vein in the lung no less
than in other parts of the body.

There is, however, in Galen nothing about circulation ,
the essence of which is movement alwavs in the same

J

direction. On the contrary, Galen emphasises the
mutual character of the exchange and of the movement.
Servetus, however, seizes on the passage and boldly
declares that ' ' the vital spirit passes from the arteries to
the veins through the anastomoses" It is a very inter-
esting illustration of how small a thing, a hint, an excep-
tional use of a word, a strained analogy, may lead to
a great discovery. It is also a remarkable illustration
of how near a great discovery a man may be without
making it. Servetus was on the very brink of such a
discovery ; indeed, he actually enunciates it, as we shall
immediately see. But he passes it by, deaf and blind to
everything save the course of his own theological argu-
ment. The one passage, the one idea, in his book that
time has shown to have been really original and important
he introduces as an incident in the course of his argument.

He tells us that he considers that blood and life or
spirit are the same in the sense that the one contains
or includes the other. He then explains that to under-
stand this we must learn how the spirit is generated
and produced in the blood. In the course of explaining
the process, he gives a perfectly clear exposition of the
lesser circulation. He no longer attributes the genera-
tion of spirit entirely to the heart, but rather to the lungs.

The vital spirit," he says, " is generated through the

mingling in the lungs of the inspired air with the subtle

blood which is communicated to it from the right ventricle

to the left. This communication does not, however,

3

34 CIRCULATION OF THE BLOOD

take place, as is generally believed, through the septum of
the heart, but by a remarkable device the subtle blood is
driven from the right ventricle through a long passage in the
lungs. It is prepared by the lungs, and is there rendered
lighter in colour, and from the artery-like vein [pul-
monary artery] it is poured into the vein-like artery
[pulmonary vein]. Then in the vein- like artery [pul-
monary vein] it is mixed with the inspired air, and by
expiration is cleansed from its fumes. So at length
completely mingled [with the air] it is drawn in by the
left ventricle during its expansion, ready to become vital
spirit." Would it be possible to describe the pulmonary
circulation better in so few words ?

That the communication and preparation," he adds,
" does take place in this way through the lungs [and not
through the septum] is moreover shown by the manifold
conjunction and communication of the arterial vein
[pulmonary artery] with the venal artery [pulmonary
vein] in the substance of the lung. This is confirmed
by the remarkable size of the venal artery [pulmonary
vein], which would not have been made so large and would
not discharge from the heart itself such a mass of pure
blood into the lungs merely for nourishment." This is
the first clear account of the lesser circulation. But can
we call it a real discovery ? Hardly. Servetus was so
near and yet so far from being a great physiologist ! But
he tells us something of the physiological questions of
his day, and he shows us how the world was, as it were,
almost consciously awaiting a solution of the ancient
problem.

Let us follow a little further the career of the man who
wrote this. After he left Paris, Servetus spent a good
deal of his time in practice as a physician at Vienne in
south-eastern France. In 1546, the year of the completion
of his work on the Restitution of Christianity, he opened

SERVETUS 35

a fatal correspondence with the theologian Calvin.
Calvin lived at Geneva, then a small Protestant republic
of which he was well-nigh dictator. Servetus sent
Calvin, along with a letter on some theological topic, a
manuscript copy of his book. Calvin was greatly in-
censed at the heretical character of the book and refused
to return it.

Even at this time Servetus knew his life was threatened,
for he wrote to a friend not long after, ' I know of a
truth that this work will be my death." He brooded
long on it. The book was recast, but not finally issued
until early in 1553. It therefore appeared before the
second edition of the great work of Vesalius. Its
heretical character was but too obvious. Although the
book was published anonymously, Servetus was sus-
pected of being its author and was arrested. He
escaped and reached Geneva, but was recognised and
again arrested. He was tried and burned alive at
Geneva on 27th October 1553. So died one of the
most remarkable figures in the annals of science.
Calvin cannot be exonerated from his share in this
cruel and wicked act, though it is said in his defence
-if such it can be called — that he would have had
him beheaded rather than burned !

When Servetus was burned, the edition of his book was
burned with him. Copies of it are therefore excessively
rare, and indeed only three are known to exist. To one
of them now in the National Library at Paris a romantic
and melancholy interest is attached. This copy was
once owned by the prosecutor of Servetus at the Genevan
trial. As he worked up his case against his unfortunate
victim, he marked the passages that he thought the most
damning, and his underlines can still be traced in the
volume. The relic has yet another interest. It bears
the marks of fire ! Perhaps it was flung into the flames

36 CIRCULATION OF THE BLOOD

along with its author, but, more fortunate than he, was
rescued by some kindly hand !

While Servetus was tried and burned at Protestant
Geneva, the Catholic authorities at Vienne had not been
idle. They, too, had tried him in his absence ; they, too,
had sentenced him to be burned alive. The sentence was
confirmed by the Catholic ecclesiastical tribunal at Vienne
after his death. It could hardly then be executed ! He
was, however, burnt in effigy, and honour was satisfied.

VI
THE SUCCESSORS OF VESALIUS

WHEN Servetus died, his work, as we have seen, was also
burned, and it could not therefore exert a wide influence.
A very few copies, however, survived, and it is probable
that these were not without their effect. Moreover, he
had been discussing the subject for years, and his opinions
were, as we have seen, an open secret. Thus it has been
thought that Servetus may have actually communicated
his opinions to a certain colleague and successor of
Vesalius at Padua, one Realdus Columbus. It is also
possible that Columbus may have secured one of the
few surviving copies of the Restitution of Christianity.

This Columbus was not a very original man, and
published nothing on physiology during his lifetime.
He had, however, written a text-book of anatomy, and
this was printed by his children in 1559 after his death.
The book is mainly based on Vesalius, whom he does not
always understand, for he denies, for instance, that the
heart is a muscle. The work of Columbus contains,
however, an important contribution to our subject —
indeed, it is the only important thing in it. The passage
bears a close resemblance to that which we have quoted
from Servetus, and runs as follows :

' Between the ventricles is the septum, through which
almost all think there is a way from the right ventricle
to the left, so that the blood in transit may be rendered
subtle by the generation of the vital spirits in order that

37

38 CIRCULATION OF THE BLOOD

the passage may take place more easily. This, however,
is an error ; for the blood is carried by the arterial vein
[pulmonary artery] to the lung. ... It is brought back
thence together with air by the venal artery [pulmonary
vein] to the left ventricle of the heart. This fact no
one has hitherto observed or recorded in writing ; yet
it may be most readily seen by any one. . . . Wherefore
I cannot wonder enough that anatomists have not ob-
served a matter so clear and of such importance. For
them it suffices that Galen said so. There are some in
our time who swear by the opinions of Galen and assert
that he should be taken as gospel, and that there is nothing
untrue in his writings." The passage seems to be a
restatement of the views of his master, Vesalius, com-
bined with those of the unfortunate Servetus. Never-
theless, it is important as the first widely distributed
description of the lesser circulation. Similar views on
the pulmonary circulation were expressed by several
somewhat later writers of the sixteenth century. None
of them, however, show any real advance on the position
of Servetus and Columbus.

The next advance in the knowledge of the circulation
was again made at Padua. It was in a sense the outcome
of the teaching of Vesalius. The most promising of the
pupils of Vesalius had been Gabriel Falloppius, a most
gifted and versatile man. Falloppius made important
contributions to anatomy and physiology, which, however,
do not bear very closely on our subject. He occupied
for some years the professorship at Padua that had been
held by Vesalius. Falloppius was in turn succeeded by
his own most promising pupil, Jerome Fabricius, who
was therefore also in the direct Vesalian tradition — the
grandson, so to speak, of Vesalius. The name Fabricius
has been held by a number of men of science. This one,
to distinguish him from his numerous namesakes, is

THE SUCCESSORS OF VESALIUS 39

usually called Fabricius of Aquapendente, after the small
Tuscan village where he was born. Fabricius of Aqua-
pendente taught anatomy at Padua for over fifty-four
years, from 1555 till his death at eighty- two in 1619.

Fabricius was a very learned man and an admirable
observer. He made many most valuable contributions
to the advancement of knowledge. Most of his works
had physiological bearings. Thus he was the founder
of modern embryology and the author of the first illus-
trated work on that subject, in which he describes the
formation of the chick in the egg. He was the first to
give accurate pictures of the structure of the eye. He
developed the mechanics of muscular movement. Almost
every department on which he touched he illumined by
striking observations, and he added to his qualities as
an observer those of a most attractive teacher.

In spite of all his powers, however, Fabricius lacked
something which, if he had possessed it, would have
placed him in the very front rank of men of science. For
a man of his scientific abilities he was extraordinarily
conservative. He never shook himself free from ancient
views, and especially he was steeped in the theories of
Aristotle and Galen. Aristotle was a very great natu-
ralist, perhaps the greatest of all time, but like all
men he made mistakes. Moreover, Aristotle had had
few predecessors in the application of scientific method,
and he had therefore less material on which to form his
opinions than have modern writers. We must, there-
fore, judge him in relation to his own time and not to
ours. But Fabricius, like many in his day, accepted
fully the theories of Aristotle, though they were often
founded on inadequate or even erroneous observations.
This backward-looking habit of Fabricius prevented his
work from being as interesting and as epoch-making as
it might otherwise have been. In connection with the

4o CIRCULATION OF THE BLOOD

circulation, for instance, he made a most striking dis-
covery, but wholly failed to draw out its most important
lesson.

In 1574 he published his book On the Valves of the
Veins. In it he says there are ' thin little membranes
on the inside of the veins distributed at intervals over
the limbs. At times they are single, at times we find two
of them together. Their mouths are directed towards
the root of the veins [that is, towards the heart], and in
the other direction [that is, away from the heart] they are
closed." (Plate VII. Fig. 5.)

It is obvious to us now that these valves hinder the flow
of blood except in the direction of the heart. Indeed,
Fabricius shows this by an actual experiment that he
describes and figures. He shows that if an arm be
lightly bandaged so as to prevent the flow of blood back
to the heart, the veins of the arm will swell up. This
we now know is because blood can get into the veins of
the arm from the capillaries but cannot get out towards
the heart because of the bandage. In an arm so bandaged
the valves will show up as nodes or swellings in the course
of the veins. Fabricius actually draws attention to this
fact. Yet all he has to say in explanation is : 'In my
opinion these valves are formed that they may to a certain
extent delay the blood and so prevent the whole of it
flowing to the feet, the hands, or the fingers and collecting
there." He thus quite failed to recognise the true
function of these valves. He was still thinking on the
old Galenic lines of the ebb and flow of blood in the
veins. He was still thinking that the use of the veins
was to convey blood back and forth, carrying nutrient
matter and natural spirits from the heart to the tissues
and bringing back the impurities from the tissues.

The great contribution of Fabricius to the problems
of the circulation was not so much his writing but his

THE SUCCESSORS OF VESALIUS 41

teaching. He was no great theorist but was a most
stimulating teacher. Above all, he taught his pupils to
observe with their own eyes. He would deserve our
remembrance if only as the master of the effective dis-
coverer of the circulation, William Harvey. It is of
interest, therefore, to ascertain what Fabricius was
actually saying about respiration, a subject so nearly
bound up with the problem of the heart's actions. We
may learn the views of Fabricius on this topic from his
work On Respiration and its Mechanism, printed in 1603.
This book still contains the old Galenic physiological
system almost unaltered.

In his summing up he tells us : "In respiration, Nature
sets herself a double end, the generation of animal spirits
and the regulation and maintenance of the innate heat.
The heat is regulated by [a relation between] the fuel
supplied, refrigeration [by the lung], and the elimination
of the superfluities. All these are the result of the air
taken into the body, whence the necessity for respiration.
. . . Respiration is the movement of air by which spirit
is taken in and given out through the mouth. In in-
spiration air enters the lung and the heart, carrying
material and coldness ; in expiration, on the other hand,
the superfluous residues are evacuated." The innate
heat of the heart was thus even more of a reality to
Fabricius than to Galen, and he is back again on
the Aristotelian view. Thus he says that " the heart
burns as with a flame." He does not even accept the
lesser circulation as demonstrated by Servetus and by
Columbus, his predecessor as teacher at Padua.

VII
HARVEY

WE have seen how nearly all of the early advances in
physiology and anatomy were made at the University of
Padua. The medical school there was undoubtedly the
best of the time. As the sixteenth century was closing,
a young Cambridge graduate named William Harvey
entered as a student at the University where Vesalius,
Falloppius, Columbus, and Fabricius had taught and
worked. This young man was destined to change all
the current ideas of the working of the body, and to
revolutionise the practice of medicine and of all the
sciences connected with it.

William Harvey was born at Folkestone in 1578, the
eldest of the nine children of Alderman Thomas Harvey.
He was educated at the King's School at Canterbury,
and went to Gonville and Caius College, Cambridge, in
1593. That college had already a strong link with Padua.
Gonville College, as it had been previously called, had
been refounded in 1557 by Dr. John Caius, whose name is
now attached to it. Caius had studied in Padua under
Vesalius as far back as 1539. Full of the stimulus of the
great teacher, he had returned to England and lectured
on anatomy in London from 1544 to 1564. Caius was,
moreover, one of the most prominent agents in this
country of the revived knowledge of Greek. An en-
thusiast for the study, he had himself translated and edited
several of Galen's anatomical works. The tradition of

42

PLATE V

(By courtesy of Sir D'ARCY POWER.)

WILLIAM HARVEY.
From the painting by CORNELIUS JANSSEN in the Royal College of Physicians.

PLATE VI

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HARVEY 43

Greek learning and Italian anatomy that Caius had
founded at Cambridge was strong in Harvey's time. It
accounts for much of Harvey's attitude towards the
ancient writers, and it may have been a factor in his
selection of Padua as his school.

In 1597, then, Harvey, having taken his degree at
Cambridge, went to Padua. Fabricius of Aquapendente
was now at the very height of his powers and fame.
Harvey became his pupil, and the greater pupil afterwards
fully acknowledged his debt to his great teacher. At
Padua there was a curious lecture room, lined with carved
oak, where Fabricius used to give his lectures by candle-
light. The old room is still standing (Plate VI.), and we can
picture the eager young Harvey, with his great, wonder-
ing, thoughtful eyes, sitting there listening and eagerly
drinking in the eloquent expositions of the greatest living
exponent of physiological science.

While Harvey was at Padua, Fabricius was reading the
proof-sheets of his work on the respiration, from which
we have already quoted. That work, therefore, gives
us a good general idea of the views that Harvey held when
he embarked on the researches that led to his great dis-
covery. In 1602 Harvey took the degree of M.D. at
Padua and returned to England. The same year saw him
capped as a Doctor of Medicine at Cambridge and settled
down to medical practice in London. In 1609 he was
elected physician to St. Bartholomew's Hospital.

In 1615 he was elected lecturer at the College of
Physicians in London. His first course was delivered
in the following year, and the manuscript notes he used
are still in existence. The notes are in a curious mixture
of English and Latin, and so badly written that they can
hardly be read. They show, however, that he had already
mastered the idea of the circular movement of the blood.
Throughout these notes, as in his book which we shall

44 CIRCULATION OF THE BLOOD

immediately discuss, Harvey urges the illustration of
the physiology and anatomy of man from that of animals.

In the section of the manuscript notebook that deals with
the heart, Harvey describes its structure and that of the
great vessels. Then he goes on to deal with the contrac-
tion of the various cavities of the heart and of the great
vessels. He terminates this short section by saying that he
has demonstrated the perpetual motion of the blood in a
circle, and that this motion is produced by the heart-beat.

In these lectures, as in his other works, Harvey shows
considerable but not remarkable learning. He pays
very great, almost excessive, homage to the ancient
writers. His respect for the ancients is perhaps some-
what unusual even for his time, an age that almost
worshipped the past. Yet his acquaintance with
Greek anatomical and physiological writings was evid-
ently mainly, if not entirely, through Latin translations.
From his frequent quotations we can make out a list
of the books that he had read, and it is evident that
his reading was typical of his age and of his own con-
servative leanings. What he omits is almost as char-
acteristic of the man as is what he inserts. His lecture
notes are full of homely references, yet he does not men-
tion the works of Shakespeare, his contemporary, nor any
of the literature of his time. The authors he quotes most
frequently are, first, Aristotle and then Galen. He was
very closely acquainted with the works of the greatest
anatomical writers of his age, Vesalius, Falloppius,
Columbus among them, and, especially and naturally,
those of his teacher, Fabricius.

The chief characteristic that separates these lecture
notes from most of the anatomical works of his time,
except those of Fabricius, is the remarkably extensive
first-hand knowledge of the anatomy of animals they
exhibit. We have seen that Fabricius had set him the

HARVEY 45

example in this matter, and the lesson had been well
learnt. The lecture notes show that by 1616 Harvey
had already dissected very carefully more than eighty
different kinds of animals. This performance is the
more remarkable when we remember that he had been
in busy practice ever since settling in London.

There is one page of the lecture notes on which we
may concentrate our attention (Plate VI.). It is only
half-filled with writing, and the actual words on the
page, copied line for line, are as follows : —

VMHconstat per fabricam cordis sanguinem
per pulmones in Aortam perpetuo
transferri, as by two clacks of a
water bellows to rayse water
constat per ligaturam transitum fanguinis
ab artery's ad venas
vnde A perpetuum sanguinis motum
in circula fieri pulsu cordis
An ? hoc gratia Nutritionis
an magis Conservationis sanguinis
et Membrorum per Infusionem calidam
vicissimque sanguis Calefaciens
membra frigifactum a Corde
Calefit.1

This, so far as it is translatable at all, may be trans-
lated as follows : —

' On account of the structure of the heart, William
Harvey is of the opinion that the blood is constantly passed

1 The passage contains two peculiar signs which need explanation.
At the beginning is the sign \f\\-\, making an abbreviated form of
the initials of William Harvey's name. He was accustomed to put
this monogram opposite statements that he thought peculiarly his
own. The other sign is the triangle A which is the capital form of
the Greek letter delta. This sign Harvey uses as an abbreviation
of the phrase " it is demonstrated."

46 CIRCULATION OF THE BLOOD

through the lungs into the aorta, as by two clacks of a water
bellows to raise water. Moreover, on account of the action
of a bandage on the vessels of the arm [see p. 58 below]
he is of the opinion that there is a transit of blood from
the arteries to the veins. It is thus demonstrated that a
perpetual motion of the blood in a circle is brought about by
the beat of the heart. What shall we say ? Is this for
the purpose of nutrition ? Or is it for the better pre-
servation of the blood and of the members by imparting
heat to them, the blood by turns losing heat as it warms
the members, and gaining heat from the heart ? '

The three sentences, " the blood is constantly passed
through the lungs into the aorta as by two clacks of a
water bellows to raise water," ' there is a transit of blood
from the arteries to the veins," and " a perpetual motion
of the blood in a circle is brought about by the beat of
the heart," conclusively prove that Harvey had already
attained to an understanding of the essential points in
the circulation of the blood.

One phrase requires a little further explanation. It
is the curious expression in which the action of the heart
in driving blood through the lungs is compared to " two
clacks of a water bellows to raise water." A clack in the
English of Harvey's day was a form of valve used on
pumps or " water bellows." Such a valve or " clack '
was opened by the upward movement of the water
produced by suction, and closed again by the backward
pressure of the weight of water. Thus a writer contem-
porary with Harvey tells us that ' ' a clacke is a piece of
Leather nayled ouer any hole hauing a peece of Lead
to make it lie close, so that ayre or water in any vessell
may thereby bee kept from going out." l The two

1 John Bate, Mysteries and Arts in foure seuerall Parts, London,
1635. The quotation we have given is fronl Part I. Of Water
Works.

HARVEY 47

clacks or valves to which Harvey refers are doubtless,
first, the valves between the auricle and ventricle which
prevent blood that has once entered the ventricle from
getting back into the auricle, and second, the valve at
the commencement of the pulmonary artery which
prevents blood once driven into that vessel from
the ventricle, from getting back again into the ventricle.

Harvey soon attained eminence in his profession. In
1618 he was appointed physician to King James i., and
he must have been very busy about the Court. He cared
little for politics, but took the Royalist side in the Civil
War, served with Charles' army, and was present at the
battle of Edge Hill. There are many indications to show
that he was widely trusted by his medical colleagues
as a wise and discreet adviser. He was not one of those
unhappy geniuses of whom it is said that ' a prophet
hath no honour in his own country ' (JOHN, chap. iv.
ver. 44). In spite of his other occupations he continued
to lecture regularly at the College of Physicians. Yet,
strangely enough, these lectures, embodying the most
revolutionary doctrine delivered by the most sober and
conservative of lecturers, seem to have attracted little
attention. Their full importance was certainly not
appreciated for some years.

Soon, however, his views were to reach a wider audience.
In 1628 there happened an event of primary importance
for the progress of science. In that year Harvey pub-
lished at Frankfurt his great work — a very great work
it is in a wonderfully small bulk. It is a badly printed
quarto volume of 72 pages, containing a very large
number of misprints. These need not surprise us when
we glance again at his handwriting ! (Plate VI.). The
book is in Latin and is called An Anatomical Dissertation
concerning the Motion of the Heart and Blood in Animals.
It is dedicated to King Charles i., who had ascended the

48 CIRCULATION OF THE BLOOD

throne three years previously, and this dedication is of
some interest as showing the cast of Harvey's mind.
He begins it by comparing the king in his kingdom
with the heart in the midst of the body. The com-
parison is borrowed from Harvey's favourite author,
Aristotle.

In the introduction which follows, Harvey sets forth
the views that had been held as to the structure of the
heart and the motion of the blood. These we have for
the most part already discussed. Then follow seventeen
chapters in which the subject is demonstrated. It is on
these chapters that Harvey's title to fame is based. We
shall attempt to epitomise them.

Harvey's book, though very convincing, is by no
means easy reading. For this there are various reasons.
Thus he frequently refers to ancient authorities, with
whom the modern reader is unfamiliar. It was necessary
for him to deal with these ancient authorities, because
they provided the current views of the seventeenth
century. To a reader nowadays, however, the constant
return to the opinion of the ancients often forms an
obstacle to the understanding of Harvey's argument. In
Harvey's time, too, men were unaccustomed to the
physiological method of research. He had therefore to
devote much of his space to justifying deductions drawn
from one creature being applied to another, matters
that are now often mere physiological commonplaces.
Again, the Latin style selected by Harvey is not well
adapted to scientific discussion. The sentences are often
exceedingly involved, and there are passages too that
are by no means easy to understand or to render. The
resulting translation is, therefore, bound to be somewhat
quaint, and Harvey, we must remember, was conserva-
tive in reading and outlook even for his own time. More-
over, the actual division and arrangement of the. subject-

HARVEY 49

matter of the book are not altogether what they might
be, and the division into chapters does not exactly
correspond to the division of subjects. Add to all this
that Harvey was evidently not a very careful or patient
proof corrector, as is shown by the large number of
printer's errors that he left in the text. Lastly, there
are great practical reasons that make it a difficult book.
One is that it is extremely condensed and contains a
vast number of facts, conclusions, and observations in
a very small space. Another is that it was the first
time that anything of the sort had been attempted, and
Harvey was grappling with a new idea.

VIII

AN EPITOME AND ESTIMATE OF HARVEY'S

WORK

(a) THE PRELIMINARY OBSERVATIONS

IN summarising this great work we shall try to avoid
its difficulties. Sometimes we shall give Harvey's con-
clusions in our own words, sometimes in his. His
antiquated references we shall mainly omit. At times
we shall rearrange his subject. It will be best to classify
his material into a series of sections, wrhich do not always
correspond to his chapters. Each of these sections
leads to a conclusion, but they will differ greatly in
length according to the amount of material to be con-
sidered or the difficulty of understanding the point with
which each deals.

1. "If the heart is grasped in the hand, it may be felt
to become harder during its action. This hardness
proceeds from tension, just as when the forearm is
grasped, its muscles are perceived to become tense and
firm when [these muscles] move the fingers."

The contraction or systole of the heart therefore
corresponds to its active position ; its expansion or
diastole corresponds to its position of rest.

2. 'It may further be observed in fishes and cold-
blooded animals [in which the heart beats long after
the death of the animal] . . . that when the heart moves
it becomes of a lighter colour, and when it is quiescent

HARVEY'S WORK 51

it becomes of a deeper blood-red colour. It thus seems
evident that during action the heart . . . becomes
erect, hard, and of diminished size. The movement is
plainly of the same nature as that of the muscles when
they contract."

During contraction the heart diminishes in breadth and
increases in length. Owing to this increase in length, the
apex of the heart strikes the chest wall during contraction
of the organ on the left side. It can be easily felt and seen
to beat under the fifth rib. A new point has here been
raised. It had naturally been believed that it was during
expansion that the heart struck the chest wall. Harvey
showed that it was during contraction that this event took
place. The point raised by Harvey had been hinted
at, however, by Leonardo, who had made experiments
which, rightly interpreted, would have led to the same
conclusion.

3. The contraction of the heart and the striking of
the apex of the heart against the chest wall are also
simultaneous, or almost simultaneous, with another
phenomenon, namely, the expansion of the arteries,
which may be felt as the pulse. The observation dis-
posed of the view, that had been held by many, that
the pulse was a result of the active expansion of the
arteries or even of the substance of the blood itself, co-
incident with the expansion of the heart. Those who held
this view thought that the expansion of the heart and the
expansion of the arteries was part of one and the same
event, an expansion extending right through the vascular
system. Harvey's new observation made it highly
probable that the contraction of the heart was the cause
of the expansion of the artery, and therefore the cause
of the pulse.

4. This third conclusion is confirmed by the character
of the bleeding from an artery that has been cut. The

52 CIRCULATION OF THE BLOOD

blood gushes forth from a severed artery by spurts.
These spurts take place at the moment when the ventricle
contracts, not when it expands.

5. The auricles can be shown to have somewhat
the same relation to the ventricles that the ventricles
have to the arteries. In the dying heart of an animal,
the ventricles cease beating before the auricles. If
the tips of the ventricles are removed so as to expose
their cavities, then each beat of the auricles will be
seen to be followed by a corresponding spurt of blood
from the opened cavity of the ventricles. In other
words, at each beat or contraction of the auricle, blood
is driven into the corresponding ventricle.

6. In the intact heart the contraction of the auricles
is followed by that of the ventricles. The same blood,
therefore, that is driven into the ventricles by the con-
traction of the auricles is subsequently driven into the
arteries by the contraction of the ventricles.

7. Once the blood has entered one of the great arteries
-whether the aorta or the pulmonary artery — it cannot

return along the path by which it came. Its movement
in that direction is absolutely stopped by valves. This,
as we have seen, had been successfully demonstrated by
previous investigators and notably by Leonardo.

8. But Harvey introduces a new point in connection
with the conclusion of paragraph 7. He points out that
this process must be continuous. This leads him to a
very crucial discussion. Consider the capacity of the
heart. Let us suppose the ventricle holds but 2 ounces
of blood. The pulse beats 72 times a minute and 72 X 60
times an hour. In the course of one hour, therefore, the
left ventricle will throw into the aorta or the right ventricle
into the pulmonary artery no less than 72 X 60x2 =8640
ounces =38 stones 8 Ib. In other words, in one hour the
ventricle will throw into the great artery more than three

HARVEY'S WORK 53

times the body weight of a heavy man. Where can all
this blood come from ? Where can it all go to ? We
know that the valves at the root of the great arteries
prevent it regurgitating. It cannot come from the in-
gested food and drink, for no one could consume so much
in one hour ! It cannot go to and remain in the tissues,
for they would soon all burst and ooze with blood !

9. But if all this blood is sent out by the arteries into
the body, and if the body itself is not large enough to
supply it, where does it come from ? It must come from
the veins, which also contain blood. This conclusion
is reinforced by a very simple piece of knowledge. The
proportion of the weight of the blood to that of the rest
of the body is known, and it is well known too that if an
artery of any size is cut, and no remedies applied, we should
bleed to death in a very short time. The bleeding would
get slower and slower until it finally ceased as the blood
was exhausted and death approached. The reason must
be that the blood, being lost, does not reach the veins
and so cannot return again from them to the arteries.
Blood does not escape in the same rapid way from severed
veins, because their walls are flabby and have little muscle
or propelling power.

10. But how does this blood get from the venous
system to the left side of the heart ? And how, too, does
it get from the arteries into the veins ? These are the
crucial questions in the whole discussion. We know the
answers to them now. Let us see how Harvey sought
to answer them.

Blood can enter the right auricle through the vena
cava, the opening of which into the right auricle is patent
and obvious. It can then enter the right ventricle, the
opening into which from the right auricle is equally
obvious, though guarded by valves. Regurgitation
through this auriculo-ventricular orifice is prevented

54 CIRCULATION OF THE BLOOD

by these very valves. From the right ventricle there is,
however, one exit, the pulmonary artery, or, as Harvey
calls it, the arterial vein. If it enters that vessel it cannot
regurgitate again, for ' ' there are three sigmoid or semi-
lunar valves at the orifice of the arterial vein [pulmonary
artery], which completely prevent blood sent into the
vessel from returning to the cavity of the heart."

The whole passage which follows is saturated with Galen,
who had gained an idea of the action of these valves with-
out being able to draw the conclusions that Harvey
reached. ' From Galen," says Harvey, " that divine
man, that Father of Physicians, it clearly appears that
blood passes through the lungs from the arterial vein
[pulmonary artery] to the small branches of the venal
artery [pulmonary vein]."

Now it may reasonably be doubted here whether
Harvey has rightly interpreted Galen. In saying that
in the works of Galen the matter clearly appears, he is
certainly giving Galen something much more than his
due. The passages in the works of Galen that refer to
this matter are neither clear nor are they even consistent
with each other. There is, however, one short para-
graph in Galen's very voluminous works which may bear
the interpretation that Harvey put on it. Whether
Galen meant it as Harvey interprets it we need not
discuss. The important thing, however, is that Harvey,
with all his over-respect for Galen, has the instincts of a
great investigator and interpreter, and can see the real
truth through Galen's verbiage. It is one of the many
cases in the history of science in which a truth half seen
or but dimly seen, and therefore imperfectly and obscurely
expressed by an earlier writer, awaited a later investigator
to grasp its nature and importance and to express it ade-
quately. To whom shall the honour be given ? It is a
question that can never be answered fully, because science

HARVEY'S WORK 55

is a continuous process, a growth, and can exist only as
growth. It is often the mark of genius that the meaning
of a phrase is fuller and deeper than even its author is
aware. Each investigator, too, must of necessity build
on the work of those who came before him, so that no
discovery is in a strict sense entirely new. It is the
demonstration of this process of growth or continuity,
and the discovery of the deeper meanings underlying
works of genius, that give its chief interest and charm to
the history of science.

Harvey's respect for Galen is thus a form — perhaps
some of his readers may think it becomes a rather
tiresome form — of the humility and modesty that has
characterised most great discoverers. He goes on attri-
buting to Galen what is effectively his own discovery :

The heart then is continually receiving and expelling
blood by and from its ventricle, and for this end is equipped
with four sets of valves — two for the expulsion of blood
and two for its admission. ... As then the blood is
continually flowing into the right side of the heart and
flowing out of the left side of the heart, it is obvious
that it must somehow pass from the vena cava into the
aorta. ... It thus clearly appears that the blood must
penetrate through the porosities of the lung from the
right to the left ventricle [to get] from the vena cava to
the aorta."

(b) THE SOLUTION

ii. Here the author pauses and makes some interest-
ing reflections.

What is now to be said on the quantity and source
of the blood which thus passes, is so novel and unheard-
off that I ... tremble lest I have mankind at large for
my opponents, so much doth wont and custom become
a second nature. Doctrine, once sown, strikes its root

56 CIRCULATION OF THE BLOOD

deep, and respect for antiquity influences all men. ... I
had long considered what was the quantity of blood
transmitted, and in how short a time its passage might
be effected. I did not find it possible that it could be
supplied by the juices of the ingested food . . . unless the
blood should somehow find its way from the arteries into
the veins, and so return to the right side of the heart."

' I now began to think whether there might not be
A MOVEMENT, AS IT WERE, IN A CIRCLE, and this I after-
wards found to be true. I 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 it is sent through the lungs, impelled by
the right ventricle into the arterial vein [pulmonary artery] . ' '

It is very strange that in the midst of this, his great
discovery, he should return again to the Aristotelian
position. But so it is ! He continues his reflections in
words which might almost be quoted from Aristotle,
or rather from a mediaeval interpretation of Aristotle.

The heart then is the beginning of life ; the Sun of the
Microcosm [that is of the human body] , even as the Sun
may be called the heart of the world. It is the heart
by whose virtue and pulse the blood is moved, perfected,
and made nutrient, and preserved from corruption and
coagulation. The heart is the Lar [that is, the god of
the hearth] which, discharging its function, nourishes,
cherishes, quickens the whole body. The heart is the
foundation of life, the source of all action."

12. Here he comes now to a conclusion which is best
stated in his own words :

' And now the cause is manifest, why in our dissec-
tions 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, so little in the left, which prob-
ably led the ancients to believe that the arteries con-

HARVEY'S WORK 57

tained nothing but spirits during the life of an animal.1
The true cause of the difference is this, that 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 arterial vein [pulmonary artery]
is prevented from passing into the venal artery [pulmonary
vein] and from thence into the left ventricle of the heart.
. . . 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 the 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 empty." This
is the reason why after death the arteries are often empty
and the veins full.

He terminates this matter by remarking : We are
now in a condition to suspect why no one has yet said
anything to the purpose upon the anastomosis of veins
and arteries, either whether or how it is effected or for
what purpose. I now enter on an investigation of that
subject."

(c) SOME CRUCIAL EXPERIMENTS

13. He proceeds to examine serpents, which have the
advantage that the heart continues to pulsate long after
the animal is dead. In serpents, too, the great blood-
vessels are very conveniently arranged for observation.
He remarks that when a serpent is laid open and the
vena cava is seized with forceps and the course of the
blood below the heart thus interrupted, the part that
intervenes between the forceps and the heart almost
immediately becomes empty. At the same time the

1 The word artery is known in Greek in the form aprypia, arteria, and,
like the word aorta, is derived from a.elpei.v, deirein, to raise or lift up.
Some of the Greeks themselves derived it from drjp, aer, meaning air,
and Harvey shared in their error.

58 CIRCULATION OF THE BLOOD

heart will become of a much paler colour than before,
even when in its state of dilatation. It also becomes
smaller, because it is no longer filled with blood which
normally reaches it from the vena cava. At last it begins
to beat more slowly, so that it seems as if it were about
to die. If, however, the impediment to the flow of blood
is removed, the colour and size of the heart are instantly
restored.

" But if the artery instead of the vein is compressed,
you will observe the part between the obstacle and the
heart, and the heart itself, to become inordinately dis-
tended, to assume a deep purple or even livid colour.
At length it is so much oppressed with blood that you will
believe it about to be choked. When, however, the
obstacle is removed, all things immediately return to their
natural state in colour, size, and impulse."

14. " Now make an experiment on the arm of a man,
using a bandage as employed in blood-letting. The best
subject is a lean man who has large veins. . . . Let the
bandage be tied round the arm and drawn as tightly as
can be borne. It will first be perceived that beyond the
bandage, neither in the wrist nor elsewhere, do the
arteries pulsate. Immediately above the bandage, how-
ever, the artery rises higher at each expansion and throbs
more violently ... as if it strove to break through the
obstacle to its current. . . . The hand retains its natural
colour and appearance, though in the course of time it
begins to get somewhat colder."

" After the bandage has been kept thus for some time,
loosen it a little. . . . The whole hand and arm will now
instantly become deeply coloured and distended, and the
veins themselves tumid and knotted. After ten or twelve
pulses the hand will be excessively distended, injected,
gorged with blood. . . ."

" Now apply the finger attentively over the artery

HARVEY'S WORK 59

which is pulsating near the bandage. At the moment
of slackening the blood will be felt to glide underneath
the finger. Moreover, he on whose arm the experiment
is being made is distinctly conscious of a sensation
of warmth as the bandage is slackened. He feels too
something, namely, a stream of blood, suddenly making
its way along the course of the vessels and diffusing
itself through the hand, which at the same time begins to
feel hot, and becomes distended."

' In connection with the tight bandage we noted that
the artery was distended and pulsated above the bandage,
but not below it. In the case of the moderately tight
bandage, on the contrary, we find the veins below, never
above, the bandage, swell, and become dilated, while the
arteries [below it] shrink. ..."

The moderately tight bandage then renders the veins
turgid and distended, and the hand full of blood. I ask,
therefore, whence is this ? Does the blood that accumu-
lates below the bandage come through the veins, or
through the arteries, or does it pass by certain hidden
pores ? Through the veins it cannot come. Still less
can it come through any system of invisible pores. It
must needs then arrive by the arteries, in conformity
with all that has been already said. That it cannot flow
in by the veins appears plain from the fact that the blood
cannot be forced towards the heart unless the bandage
be removed, and when this is done, suddenly all the veins
collapse, and disgorge themselves of their contents into
the superior parts, the hand at the same time resuming its
natural pale colour. . . . Moreover, if a man has had his
arm thus bound for some little time with a moderately
tight bandage, so that it has not only got swollen and
livid, but cold, and if the bandage then is loosened, he
feels something cold make its way upwards along with
the returning blood. ..."

60 CIRCULATION OF THE BLOOD

1 Further, when the bandage is relaxed from extreme
tightness [to moderate tightness], we see the veins below
the bandage instantly swell up and become gorged, while
the arteries meantime continue unaffected, this is an ob-
vious indication that the blood passes from the arteries
into the veins, and not from the veins into the arteries."

This shows that there must therefore be either an
anastomosis of the two [kinds] of vessels, or passages in
the flesh and solid parts that are permeable by the blood.
It shows too that the veins themselves have frequent
communications with one another, because they all be-
come turgid together, with the moderately tight bandage
. . . and, moreover, if any single small vein be then
pricked with a lancet, they all speedily shrink."

15. " We have now spoken of the blood that passes
through the heart and the lungs . . . [and of the blood
that passes] from the arteries into the veins in the peri-
pheral parts and the body at large. We have yet to
explain, however, in what manner the blood finds its way
back to the heart from the extremities by the veins, and
how and in what way these are the only vessels that
convey the blood from the external to the central parts."

The celebrated Hieronymus Fabricius of Aquapen-
dente, a most skilful Anatomist, and venerable old man
. . . made representations of valves in the veins. . . .
These are situated at different distances from each other,
and diversely in different individuals . . . and are directed
upwards or towards the trunks of the veins. . . . (Plate
VII. Fig. 5.) If therefore anything attempted to pass from
the trunks into the branches of the veins, or from the greater
vessels into the less, they completely prevent it. ..."

The discoverer of these valves did not rightly under-
stand their use, nor have others added anything to our
knowledge. Their function is by no means explained
when we are told that it is to hinder the blood, by its

HARVEY'S WORK 61

weight, from all flowing into inferior parts." They do
not, in fact, always do this, " for the valves in the jugular
veins [in the neck] hang downwards, and are so arranged
that they prevent the blood from rising upwards ; in
a word, the valves do not invariably look upwards, but
always towards the trunks of the veins, invariably towards
the seat of the heart"

1 6. Now comes the real explanation of the action of
the valves of the veins, on which much of Harvey's
theory turns. These valves are solely lest the blood
should pass from the greater into the lesser veins . . .
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."

* And this I have frequently experienced in dissec-
tions of the veins. If I attempted to pass a probe from
the trunk of the veins into one of the smaller branches,
I found it impossible to introduce it far by reason of the
valves ; whilst, on the contrary, it was easy to push it
along in the opposite direction, from the branches to-
wards the trunk."

That all this may be made the more apparent, let an
arm be tied up above the elbow at A, A (Plate VII. Fig. i).
In the course of the veins, especially in labouring men and
those whose veins are large, are certain knots or elevations
as at B, C, D, E, and F, which will now be seen. These
knots are not only at the places where the veins branch, as
at E and F, but also where they do not, as at C and D.
These knots are formed by valves, which thus show them-
selves externally."

' If you now press blood from the space above one of
the valves, as from H to O (Plate VII. Fig. 2), and keep the
point of the finger upon the vein below, you will see no
influx of blood from above. The portion of the vein be-
tween the point of the finger and the valve O will remain

62 CIRCULATION OF THE BLOOD

empty. Yet the vessel will continue sufficiently distended
above that valve, as at O, G. ... If you now apply a
finger of the other hand upon the distended part of the
vein above the valve O (Plate VII. Fig. 3), and press down-
wards, you will find that you cannot force the blood
through or beyond the valve. . . . You will only see the
portion of vein between the finger and the valve become
more distended, while the portion of the vein below the
valve (H, O, Plate VII. Fig. 3) still remains empty."

" It therefore appears that the function of the valves
in the veins is the same as that of the three sigmoid valves
at the commencement of the aorta and pulmonary artery,
namely, to prevent all reflux of the blood that is passing
through them."

" Further, the arm being bound at A, A as before, and
the veins full and distended, compress a vein with one
finger L (Fig. 4), at a point below a valve or knot. Then
with another finger stroke the blood upwards beyond the
next valve N. You will now perceive that this portion
of the vein L, N still continues empty. . . . But if the
finger first applied (H, Fig. 2, L, Fig. 4) is removed, the
vein is immediately filled from below, and the arm be-
comes again as at D, C (Fig. i)."

" That the blood in the veins therefore proceeds from
more remote to less remote parts and towards the heart,
moving always in the vessels in this, and not in the con-
trary direction, appears most plain . . . for the veins
are free and open conduits of the blood returning to the
heart, and are yet effectually prevented from serving as its
channels of distribution from the heart."

(d) SUMMARY AND CONCLUSION

17. " Now I may give my view of the circulation of the
blood and propose it for general adoption."

" All things, both argument and ocular demonstration,

HARVEY'S WORK 63

confirm that the blood passes through lungs and heart by
the force of the ventricles, and is driven thence and sent
forth to all parts of the body. There it makes its way into
the veins and pores of the flesh. It flows by the veins
everywhere from the circumference to the centre, from
the lesser to the greater veins, and by them is discharged
into the vena cava and finally into the right auricle of the
heart. [The blood is sent] in such a quantity, in one
direction, by the arteries, in the other direction by the
veins, as cannot possibly be supplied by the ingested
food. ... It is therefore necessary to conclude that the
blood in the animals is impelled in a circle, and is in a
state of ceaseless movement ; that this is the act or func-
tion of the heart, which it performs by means of its pulse ;
and that it is the sole and only end of the movement and
pulse of the heart."

We have now come to an end of Harvey's discovery,
and have let him tell of it, as far as possible, in his own
words. We have seen how the power of words, words
such as innate heat, spirits, and anastomosis, had their
influence in helping or retarding the course of knowledge.
Words at different ages have different meanings, and at
any age the exact and precise meaning of a word is often
difficult to define. Often, however, much hangs on the
exact interpretation of a scientific term. Science is, of
course, concerned with observations and with inferences
from them, not with words about them. But our know-
ledge of observations and inferences can only be expressed
in words. Scientific nomenclature, therefore, though of
secondary importance, must not be despised. Harvey's
discovery introduced a very striking change into physio-
logical nomenclature, a change to which we have often
referred in the pages of this work.

In the old physiology the arteries were considered as

64 CIRCULATION OF THE BLOOD

distributing spirit and a higher form of vital activity,
while the veins distributed nourishment and the lowest
forms of vital activity. The arteries arose from the heart,
and the veins, it was thought, from the liver. The words
artery and vein meant something different of old to what
they mean to us. The two systems, arterial and venous,
were recognised to be intimately connected. Both were
linked with the heart, though the relation of the arteries
was the closer. One branch of the venous system,
however, opened into the right cavity of the heart.
The vessel, therefore, that arose from that cavity and
linked it with the lung was thus really a branch of the
venous system, and was therefore a " vein." It had thick
walls like an artery and was therefore called the arterial
vein. It is the vessel we now call the pulmonary artery.

A companion to this vessel connected also the left
cavity of the heart with the lung. As a derivative of the
left side of the heart from which the aorta arose, it was
regarded as an " artery." Its walls, however, were thin
like a vein, and it was called, therefore, the venal artery.
It is the vessel we now call the pulmonary vein.

A result of the discovery of Harvey was the intro-
duction of a new nomenclature. For us who look at the
circulation from his point of view, new names are needed.
The arterial vein has become the pulmonary artery, and
the venal artery has become the pulmonary vein. For
us an artery is a vessel which takes blood from the heart
and a vein is a vessel which takes blood to the heart.
For the men of Harvey's day arteries were distinguished
from veins by containing a different kind of blood. They
had no idea of the constant and massive change of arterial
into venous, and of venous into arterial blood. Our
conception of the difference between artery and vein
is controlled by our idea of the circulation introduced
by Harvey. A new nomenclature was therefore needed

HARVEY'S WORK 65

or, at least, a new application of the old nomenclature.
The test was specially applied in the case of the lesser
circulation, when the old arterial vein became the new
pulmonary artery, and the old venal artery became the
new pulmonary vein.

It is a change that Harvey himself foresaw, for he asks :
" Why does not the arterial vein pulsate seeing that it
should be numbered among the arteries, and why does the
venal artery have no pulse [though it is a vein] ? It is
because the pulse is the impulse of arterial blood."

" Why do the arteries have coats so much thicker and
stronger than those of the veins ? Because they have to
sustain the shock of the impelling heart and the blood that
bursts forth therefrom."

" Why has the so-called arterial vein the structure of
an artery, and the so-called venal artery the structure of
a vein ? Because in function and constitution and every-
thing else the former is in fact an artery, and the latter is
in fact a vein."

But almost in the last words in his book the great in-
vestigator returns again to Aristotle, with whom he started.
The imposing Aristotelian scientific system was at that
very moment tumbling about the ears of the philosophers,
destroyed by Galileo. But Harvey ends as he began,
relying on Aristotle for what, even in those days, was an
antiquated and demonstrably false view of the heart and
its place in the animal economy.

" Are we to agree the less with Aristotle," he asks,
' in regard to the sovereignty of the heart ? Or, on the
other hand, are we to inquire whether it receives sense
and motion from the brain, and blood from the liver ? and
whether it be the origin of the veins and of the blood ?
They who affirm these latter propositions against Aristotle,
overlook, or do not rightly understand . . . that the heart is
the first part which exists, and that it contains within itself

5

66 CIRCULATION OF THE BLOOD

blood, life, sensation, motion, before either the brain or
the liver were in being, or had appeared distinctly, or, at
all events, before they could perform any function. The
heart, ready furnished with its proper organs of motion,
like a kind of internal creature, is of a date anterior to the
body : first formed, nature willed that it should after-
wards fashion, nourish, preserve, complete the entire
animal, as its work and dwelling-place : the heart, like the
prince in a kingdom, in whose hands lie the chief and
highest authority, rules over all ; it is the original and
foundation from which all power is derived, on which all
power depends in the animal body."

Human beings are queer and incomprehensible
mixtures, and great scientific discoverers no less so
than other men ! Often accounts of great scientists
are written as though they had no faults or failings.
A wiser way is to remember that these exist, but to con-
centrate rather on the really important events in their
lives, the thoughts and influences and teaching that led up
to their great discoveries. This we have tried to do with
Harvey and the Circulation of the Blood.

How slight a thing determines a discovery ! An
accident, a suggestion, an analogy, a phrase, a word, even
a word misunderstood ! Many have tried to set forth a
complete method of research. One there was in England
in Harvey's time who devoted a vast amount of energy
and ability to the task. Francis Bacon, Lord Chan-
cellor of England, made such an attempt. Harvey
esteemed him and his method little. Of him he is
reported to have said, ' He writes philosophy like a
Lord Chancellor." Bacon, who himself showed little
skill in experiment and no aptness for discovery, yet
drew up a complete scheme for the investigation of
Nature ! It is a scheme that has never been acted on.

Such formulae for the conduct of scientific research

HARVEY'S WORK 67

have, in fact, seldom or never been used by working
scientists. For the truth is there is no one method of
science : there are as many methods as there are men of
science, though doubtless most of those working at any
particular science have much in common. The task of
the man of science is first to observe the appearances
which Nature presents, then to ascertain what lies behind
those appearances, and, lastly, to link together his con-
clusions and observations into general laws. How he
does this is not a matter of much concern, so long as he
does it. Nor need he, as a man of science, concern
himself with the question of what are the ultimate truths
behind all the appearances that Nature presents to us.
He has but to express general laws according to the know-
ledge of his day, knowing full well that a day will almost
certainly come when his general laws and the ideas on
which they are based will have to be modified or replaced.
What is a matter of concern, however, and what does
vitally affect the course of science is not how his ideas come
to him, but how he proves or verifies the statements that he
makes. The vague analogies, the loosely put suggestions,
the confused reasoning of a Servetus may have the same
source as the finely worked out conclusions of a Harvey.
The two men are poles asunder when it comes to verifica-
tion. Servetus is content with a statement, the other
passes cautiously from observation to inference, from
inference to verification in an orderly and stately sequence.
We may note, too, the careful way in which Harvey limits
his problem. He refuses to be drawn beyond his subject.
He will deal only with the knowledge that he has, knowing
full well that further work may throw new light on his in-
vestigations. He sets out to discover the mechanical explana-
tion of the movement of the heart, and he accomplishes
his task triumphantly. But he will not be led aside by
those ancient wills-o'-the- wisp, the discussion of the nature

68 CIRCULATION OF THE BLOOD

of the spirits or of the innate heat. " Whether or not the
heart," he says, " besides propelling the blood, giving it
movement and distributing it to the body, adds anything
else to it — heat, spirit, perfection — must be decided on
other grounds. So much may suffice at this time, when
it is shown that by the action of the heart the blood is
transfused through the ventricles from the veins to the
arteries, and distributed by them to all parts of the body."
A word may finally be added as to the reception of
Harvey's theory. On the whole he was fortunate in
meeting less opposition than most great innovators. In
the early years after the publication of his work, he might
reasonably have complained of neglect, but he met no very
great or embittered criticism. In spite of the dis-
belief of several eminent physiologists his views gained
ground, gradually and slowly it is true, but very surely
and steadily. He lived to have the rare pleasure of
seeing them generally accepted.

PLATE VII

FIGS. 1-4. EXPERIMENTS ON BANDAGED ARM. From HARVEY.
FIG. 5. DISSECTION OF VEIN IN THIGH AND LEG TO SHOW VALVES.

From FABRICIUS,

PLATE VIII

Fig.6.

FIG. i. LUNG OF FROG, MAGNIFIED, SHOWING CAPILLARIES. From MALPIGHI.
FIG. 2. CAPILLARY NETWORK IN TAIL OF EEL. FVom LEEUWENHOEK.

A, C, E are Veins, and B, D, F are Arteries.

FIG. 3. RED BLOOD CORPUSCLES OF SALMON. From LEEUWENHOEK.
FIGS. 4 AND 5. HUMAN RED BLOOD CORPUSCLES. From LEEUWENHOEK.
FIG. 6. HUMAN RED BLOOD CORPUSCLES DRAWN FROM THE OBJECT UNDER

A MODERN MICROSCOPE.

IX

THE DISCOVERY OF THE CAPILLARIES AND

BLOOD CORPUSCLES

HARVEY had demonstrated conclusively that the blood
did circulate. There was one part of the circulation,
however, that he left still a matter of inference. He had
shown that the blood passed from arteries to veins, but
he had not actually seen the passage. We now know that
the stream goes through the capillary network. To see
this, however, a microscope is necessary.

The microscope had been discovered in Harvey's
time and long before the publication of his work on the
circulation of the blood. Galileo had demonstrated its
value as early as 1610. A few years later the instrument
was brought to England. Nothing of real importance,
however, was revealed by microscopic research until
after Harvey's death in his eightieth year in 1657. ^
is therefore not remarkable that he made no use of the
instrument. A short time after his death his work
was completed by the investigations of certain micro-
scopic observers.

The compound microscope, as we have seen, was first
made into an effective instrument by Galileo. It was,
as it were, a by-product of his invention of the telescope.
With his new instrument Galileo explored the heavens and
made many new and important discoveries. He demon-
strated the rings of the planet Saturn, he saw the satellites

of Jupiter, and he examined the spots on the sun and the

69

70 CIRCULATION OF THE BLOOD

craters on the surface of the moon. Galileo saw enough
with his telescopes to convince himself that the movement
of the sun round the earth was but an appearance. At
the very time that Harvey was giving his first course of
lectures securely in London, Galileo's teaching was
attracting the unwelcome attention of the Inquisition in
Rome.

Galileo's microscopes, however, were far less satis-
factory than his telescopes. For optical reasons, the
nature of which we need not discuss, these early com-
pound microscopes failed to give a clear picture. With
any high degree of magnification the image was always
blurred and distorted. The seventeenth century had
more than passed its first half before a better device was
introduced. But soon after 1650 a way was found of
improving simple lenses of very high power. Even the
improved high power simple lenses only gave a clear
image of an exceedingly small area. Within that small
area, however, the image was quite clear and was not
much distorted. Many of the most important micro-
scopical discoveries of the second half of the seventeenth
century were therefore made with a simple lens. This
was notably the case with much of the work of the great
investigators, Marcello Malpighi, Jacob van Swammer-
dam, and Anthony van Leeuwenhoek, with whose work
on the circulation we must now briefly deal.

Malpighi was born near Bologna in northern Italy in
1628, the year that Harvey's work was published. He
went as a student of philosophy to the University of
Bologna, but, having lost his parents, he changed his
course for that of medicine. He very soon developed
great ability in scientific research, and was especially
skilled in minute investigation. He took a medical
degree, and soon after, in 1656, was elected professor of
medicine at his own university.

CAPILLARIES AND CORPUSCLES 71

Malpighi had as yet written nothing, but his penetra-
tion and sagacity were early recognised by his colleagues.
His singular beauty and simplicity of character were
evident to all. His special skill in minute anatomy also
soon drew attention. From an early date these qualities
of his became known in England, and nearly all his works
were published in London by and at the expense of our
own Royal Society. The only one of Malpighi's pub-
lications with which we are here concerned, however, is
his first. It was printed not in London but in Bologna,
in 1 66 1, under the title Anatomical Observations on the
Lungs.

In this work Malpighi supplied the missing element
in the investigations of Harvey. He was the first man
who saw the actual passage of blood from arteries to
veins. He saw the capillaries of the lesser or pulmonary
circulation. The object which first yielded up the secret
was the lung of the frog. This organ in the frog happens
to be almost transparent. It is also very simple in
structure, and is furnished on its surface with particu-
larly conspicuous capillary vessels. Malpighi could
hardly have selected a more suitable object for the
purposes of this research. We may let him tell his
own story.

He tells us that while to the naked eye " the frog's
lung is nought but a membranous bladder ... to
observation with the microscope it yields something
much more remarkable." In the tiny vessels on the
surface of the lung he could see that " the blood is forced
and scattered by the pulse through the arteries into a
network. ... As the blood stream, thus repeatedly
divided up, is carried round in a sinuous manner, its
colour fades. It is thus distributed until it approaches
the walls . . . receiving branches of the veins. . . .
While the heart is still beating, two movements in

72 CIRCULATION OF THE BLOOD

opposite directions can be seen, making the circulation
of the blood quite evident. The same may be seen even
better in the mesentery. ..."

" With unaided vision [and without the help of a
microscope] I might have believed that the blood escaped
into an empty space and was re-collected again by a
gaping vessel, but for the tortuous and scattered move-
ment of the blood in different directions and its union
again into a definite vessel. . . . Such is the branching
character of these vessels as they proceed on the one side
from the artery and [are gathered] again on the other
side to the vein . . . that there appears to be a network
made up of the continuations of the two vessels. . . .
Hence it appears to the senses that the scattered blood
flows along tortuous vessels, and is not poured out
into spaces, but always continues in tubules, and that
its dispersion is due to the multiple winding of the
vessels" (Plate VIII. Fig. i).

A few years later Malpighi made a further important
observation, the nature of which he failed to interpret
adequately. Till his time and beyond, the colour of the
blood was believed to be diffused through its substance.
We now know that it is concentrated in the so-called
red corpuscles, the minuteness of which gives the sus-
pension— for such it is — the appearance of being a uni-
form red fluid. Malpighi caught a sight of these particles
through his lenses, but he misinterpreted them. In
examining a hedgehog he tells us that in a blood-vessel
of the omentum ' I saw globules of fat, of a definite
outline and red colour. They were like a chaplet of red
coral." These globules were the red corpuscles, and in
the " chaplet " they were collecting together in rouleaux
as they are very liable to do.

Similar observation of blood corpuscles had been made
by several of Malpighi's contemporaries. Thus in 1658

CAPILLARIES AND CORPUSCLES 73

a German Jesuit named Kircher, in giving a very con-
fused account of the plague, had described microscopic
bodies in the blood of plague patients. He rushed to the
conclusion that they were the cause of plague, but they
were, in fact, rouleaux of blood corpuscles.

A better account was given by a Dutchman, Jacob van
Swammerdam, at a date somewhat later than Malpighi's
discovery. This Swammerdam was a most -remarkable
character, who in some respects resembled Servetus. Had
he lived a century or so earlier he might have suffered
the same fate. As it was, he passed his short life in com-
parative peace, though tortured by the misgivings of a
diseased mind. His unstable and fanatical temper pre-
vented him from publishing much work in his lifetime.
He died in 1680, and fifty years afterwards the manu-
script of his great Bible of Nature was rescued and pub-
lished. It is one of the most beautifully illustrated works
on natural history that has ever been produced, and is a
storehouse of valuable information, to which naturalists
often turn even nowadays.

In that work Swammerdam wrote : ' I saw a serum in
the blood [of a frog] in which were a vast number of
roundish particles, of a flat, oval, but regular form. . . .
When I viewed them sideways they resembled crystalline
clubs, or other figures, according as they were turned
about in various directions in the serum of the blood. I
observed besides that the colour of the objects always
appeared the more faint the more they were magnified
with a microscope." These were the red corpuscles.
It should be added that Swammerdam says elsewhere
that he thought he saw globules in the human blood,
though he was inclined to think that they were formed
after it had been removed from the body, and were
not found in the blood while still confined in the
vessels.

74 CIRCULATION OF THE BLOOD

The last writer whose work we have to consider is
Anthony van Leeuwenhoek, another Dutchman, whose life
covered nearly a century, for he lived from 1632 to 1723.
Leeuwenhoek was a man in a humble walk of life who
never rose above the station of usher to a court in a small
Dutch town. He owed nothing to any teacher or any
university, and spoke and wrote no language but his own.
In his youth there had been in Holland a widespread
interest in Optics, and he developed remarkable skill
as an amateur lens maker. His lenses got better and
better, until finally he was making the best high power
lenses in Europe.

At the same time Leeuwenhoek developed great talent
as an observer and as a shrewd interpreter of what he
observed. He did not publish anything until he was over
forty. In 1674, however, a specimen of his work was
sent to the Royal Society. The importance of it was at
once perceived, and it was translated and appeared in the
transactions of that learned body. From then on he
corresponded regularly with the Society, who printed all
or nearly all his work.

At first Leeuwenhoek did not believe in the circula-
tion of the blood. He remained sceptical long after most
better informed and better educated men had become
convinced. He retained this attitude as late as 1686,
when, however, he began to waver. By 1688 he had
completely changed his opinions, for, in that year, owing
to the perfection that his microscopes had then reached,
he clearly saw not only the systemic capillary circulation,
but also the actual passage of the blood corpuscles
through the minute capillaries. He described the
capillary circulation in the web of the frog's foot, in
the mesentery of the same animal, and in the tails
of young fish (Plate VIII. Fig. 2). He described and

CAPILLARIES AND CORPUSCLES 75

figured clearly and accurately enough the blood corpuscles
of frogs and other cold-blooded creatures (Plate VIII.
Fig. 3), and also saw and figured — though rather less
accurately — the blood corpuscles of man (Plate VIII. Figs.
4 and 5). The ocular demonstration of the circulation of
the blood was thus at last complete.

BIBLIOGRAPHY

I. GENERAL WORKS ON SCIENTIFIC METHOD.

NORMAN CAMPBELL, What is Science ? (Methuen.) 1921, 53.
Sir R. A. GREGORY, Discovery, the Spirit and Service of Science.

(Macmillan.) Tenth Edition, 1921, 73. 6d.
KARL PEARSON, The Grammar of Science. (A. & C. Black.)

Third Edition, 1911, los.
F. W. WESTAWAY, Scientific Method, its Philosophy and its

Practice. (Blackie.) Second Edition, 1919, IDS. 6d.

II. SPECIAL WORKS ON CIRCULATION OF THE

BLOOD.

ANTIQUITY.

CHARLES SINGER, Greek Biology and Greek Medicine. (Clar-
endon Press.) 1922, 35.

LEONARDO AND THE RENAISSANCE.

H. HOPSTOCK in Charles Singer's Studies in the History and
Method of Science. Vol.11. (Clarendon Press.) 1921,
483. Other material on this topic can be found in Vol. I.
(now out of print) of the same work.

VESALIUS AND HIS FOLLOWERS.

MICHAEL FOSTER, Lectures on the History of Physiology.
(Cambridge University Press.) 1901, I2S. 6d.

77

78 CIRCULATION OF THE BLOOD

SERVETUS.

The literature on Servetus is very scattered, but the article on
him by the Rev. ALEXANDER GORDON in the Eleventh
Edition of the Encyclopaedia Britannica is reliable.

HARVEY.

An Anatomical Disquisition on the Motion of the Heart and
Blood in Animals, by WILLIAM HARVEY, translated from
the Latin by ROBERT WILLIS. (Dent, Everyman
Library.) 2S.

J. G. CURTIS, Harvey's Views on the Use of the Circulation of
the Blood. (New York, Columbia University Press ;
London, Humphrey Milford.) 1915, 6s. 6d.

Portraits of Dr. William Harvey. (Milford.) 1913, 2is.

THE MICROSCOPISTS.

L. C. Mi ALL, The Early Naturalists, their Lives and Work,
1530-1780. (Macmillan.) 1912, los.

INDEX

ALEXANDRIA, school of, n.
Anastomosis between veins and

arteries, 33, 63.
,, meaning of the

Greek word, 32.
Aortic valves, 6, 8.
Aristotle on heart, 10, n.

,, on innate heat, 16.
Arterial vein = pulmonary artery,

6, 13, 38, 54, 64.
Arteries, distinction from veins,

3, 65.
Auricles, described by Leonardo,

20.

Bacon, Lord Francis, 66.
Berengar of Carpi, 21, 22.
Bologna, Malpighi at, 70, 71.

Caius, John, 42.

Calvin, 35.

Capillary blood-vessels, i, 7, 71,

74-
Circulation, lesser and greater,

distinguished, 5.
,, as first enunciated

by Harvey, 45.
,, described, i-io.

,, Harvey's work on,

epitomised, 50-68.
,, meaning of term, 5.

College of Physicians, 43, 47.
Columbus, Realdus, 36-37.
Corpuscles of blood, 72-75.

Egyptian ideas on pulse, 10.

Fabricius of Aquapendente, 38-
41, 43, 60.

,, on respiration, 41.

,, on valves of veins, 40.
Falloppius, Gabriel, 38.

Galen on anastomosis, 32, 33,

54-
,, on heart, 12-17.

Galen's physiology, persistence

of, 12, 18, 25, 54.
Galileo, 69.
Geneva, Calvin at, 35.

,, Servetus at, 35.
Greek, revived knowledge of,

18.

Harvey, 9, 43-68.

,, experiments on band-
aged arm, 58-62.
,, his death, 69.
,, in Cambridge, 42.
,, in London, 43 ff.
,, in Padua, 43.
Harvey's Anatomical Disserta-
tion, 47.

,, first enunciation of cir-
culation, 45.
,, handwriting, 43.
,, lecture notes, 43-46.

style, 43,48.

Heart, structure of, 6 and through-
out.
Hippocrates on pulse, 10.

Innate heat, 16, 17, 41, 63, 67.

Latin, importance of, in six-
teenth century, 24.
Leeuwenhoek, Anthony van, 74.
Leonardo da Vinci, 19.

,, on heart, 21.

,, on respiration, 20,

Malpighi, 70.

,, on capillaries, 71.

Methods, scientific, 67.
Middle Ages, physiology in, 18.

79

8o

CIRCULATION OF THE BLOOD

Padua, anatomy at, 24, 37, 38,

42,43-
,, ancient theatre at, 43.

Paris, anatomy at, 23.
Pulmonary artery =arterial vein,

6, 13, 38, 54, 64-
,, vein = venal artery,

14, 15, 20, 25, 38,

64.
Pulse, i, 10.

Renaissance, 18.

Royal Society publishes Leeuwen-
hoek's work, 74.
„ ,, publishes Mal-

pighi's work, 71.

Septum, supposed pores in, 6,
13, 14, 21, 25, 27, 28, 34,

37-

Servetus, 29-36.

,, his martyrdom, 35.

,, on nature of blood, 30-

32.

Spirits, 15, 16, 33, 37, 63, 67.
Swammerdam, Jacob van, 73.

Valves, aortic, 6, 21.

,, auriculo-ventricular, 6.

,, of veins, 3, 40, 60.

,, pulmonary, 6, 21, 53.
Veins, distinction from arteries,

3-
Ven-a cava, 3, 7, 53.

Venal artery =pulmonary vein,

14, 15, 20, 25, 38, 64.
Vesalius, 23-28.

,, his criticism of Galen,

27, 28.
Vienne, Servetus at, 34.

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