The importance of Harvey’s discovery
of the circulation of the blood can only be properly
estimated by bearing in mind what was done by his
predecessors in the same field of inquiry. Aristotle
had taught that in man and in the higher brutes the
blood was elaborated from the food in the liver, conveyed
to the heart, and thence distributed by it through
the veins to the whole body. Erasistratus and
Herophilus held that, while the veins carried blood
from the heart to the members, the arteries carried
a subtle kind of air or spirit. Galen discovered
that the arteries were not merely air-pipes, but that
they contained blood as well as vital air or spirit.
Sylvius, the teacher of Vesalius, was aware of the
presence of valves in the veins; and Fabricius, Harvey’s
teacher at Padua, described them much more accurately
than Sylvius had done; but neither of these men had
a true idea of the significance of the structures
of which they wrote. Servetus, the friend and
contemporary of Vesalius, writing in 1533, correctly
described the course of the lesser circulation in
the following words: “This communication
(i.e. between the right and left sides of the
heart) does not take place through the partition of
the heart, as is generally believed; but by another
admirable contrivance, whereby from the right ventricle
the subtle blood is agitated in a lengthened course
through the lungs, wherein prepared, it becomes of
a crimson colour, and from the vena arterialis (pulmonary
artery) is transferred into the arteria venalis
(pulmonary vein). Mingled with the inspired air
in the arteria venalis, freed by respiration
from fuliginous matter, and become a suitable home
of the vital spirit, it is attracted at length into
the left ventricle of the heart by the diastole of
the organ.” But when Servetus comes to speak
of the systemic circulation, what he has to say is
as old as Galen.
The opinions, therefore, on the subject of the blood and its
distribution which were prevalent at the end of the sixteenth century prove
(1) That although the blood was not regarded
as stagnant, yet its
circulation,
such as is nowadays recognized, was unknown;
(2) That one kind of blood was thought to flow
from the liver to the
right ventricle,
and thence to the lungs and general system by
the veins,
while another kind flowed from the left ventricle to
the lungs
and general system by the arteries;
(3) That the septum of the heart was regarded
as admitting of the
passage
of blood directly from the right to the left side;
(4) That there was no conception of the functions
of the heart as the
motor power
of the movement of the blood, for biologists of that
day doubted
whether the substance of the heart were really
muscular;
they supposed the pulsations to be due to expansion
of
the spirits
it contained; they believed the only dynamic effect
which it
had on the blood to be that of sucking it in during
its
active diastole,
and they supposed the chief use of its constant
movements
to be the due mixture of blood and spirits.
This was the state of knowledge before Harveys time.
By his great work he established
(1) That the blood flows continuously in a circuit
through the whole
body, the
force propelling it in this unwearied round being the
rhythmical
contractions of the muscular walls of the heart;
(2) That a portion only of the blood is expended
in nutrition each time
that it
circulates;
(3) That the blood conveyed in the systemic
arteries communicates heat
as well
as nourishment throughout the body, instead of exerting
a
cooling
influence, as was vulgarly supposed; and
(4) That the pulse is not produced by the arteries
enlarging and so
filling,
but by the arteries being filled with blood and so
enlarging.
We can now consider the method by
which Harvey arrived at these results. The work,
“De Motu Cordis et Sanguinis, after giving an
account of the views of preceding physiologists, ancient and modern, commences
with a description of the heart as seen in a living animal when the chest has
been laid open and the pericardium removed. Three circumstances are noted
(a) The heart becomes erect,
strikes the chest, and gives a beat;
(b) It is constricted in every
direction;
(c) Grasped by the hand, it
is felt to become harder during the
contraction.
From these circumstances it is inferred
(1) That the action of the heart is
essentially of the same nature as
that of voluntary muscles, which become hard
and condensed when
they act;
(2) That, as the effect of this, the
capacity of the cavities is
diminished, and the blood is expelled;
(3) That the intrinsic motion of the heart is
the systole, and not the
diastole,
as previously imagined.
The motions of the arteries are next
shown to be dependent upon the action of the heart,
because the arteries are distended by the wave of
blood that is thrown into them, being filled like sacs
or bladders, and not expanding like bellows.
These conclusions are confirmed by the jerking way
in which blood flows from a cut artery.
In the heart itself two distinct motions
are observed first of the auricles, and
then of the ventricles. These alternate contractions
and dilatations can have but one result, namely,
to force the blood from the auricle to the ventricle,
and from the ventricle, on the right side, by the
pulmonary artery to the lungs, and on the left side
by the aorta to the system.
These considerations suggest to the mind of Harvey the idea
of the circulation. I began to think, he says, whether there might not
be a motion, as it were, in a circle. This is next established by proving
the three following propositions:
(1) The blood is incessantly transmitted by
the action of the heart
from the
vena cava to the arteries in such quantity
that it
cannot be
supplied from the ingesta, and in such wise that the
whole mass
must very quickly pass through the organ;
(2) The blood, under the influence of the arterial
pulse, enters, and
is impelled
in a continuous, equable, and incessant stream
through
every part and member of the body, in much larger
quantity
than were sufficient for nutrition, or than the whole
mass of
fluids could supply;
(3) The veins in like manner return this blood
incessantly to the heart
from all
parts and members of the body.
As to the first proposition Harvey
says, “Did the heart eject but two drachms of
blood on each contraction, and the beats in half an
hour were a thousand, the quantity expelled in that
time would amount to twenty pounds and ten ounces;
and were the quantity an ounce, it would be as much
as eighty pounds and four ounces. Such quantities,
it is certain, could not be supplied by any possible
amount of meat and drink consumed within the time
specified. It is the same blood, consequently,
that is now flowing out by the arteries, now returning
by the veins; and it is simply matter of necessity
that the blood should perform a circuit, or return
to the place from whence it went forth.”
Demonstration of the second proposition that
the blood enters a limb by the arteries and returns
from it by the veins is afforded by the
effects of a ligature. For if the upper part of
the arm be tightly bound, the arteries below
will not pulsate, while those above will throb violently.
The hand under such circumstances will retain its natural
colour and appearance, although, if the bandage be
kept on for a minute or two, it will begin to look
livid and to fall in temperature. But if the
bandage be now slackened a little, the hand and the
arm will immediately become suffused, and the superficial
veins show themselves tumid and knotted, the pulse
at the wrist in the same instant beginning to beat
as it did before the application of the bandage.
The tight bandage not only compresses the veins, but
the arteries also, so that blood cannot flow through
either. The slacker ligature obstructs the veins
only, for the arteries lie deeper and have firmer coats.
“Seeing, then,” says Harvey, “that
the moderately tight ligature renders the veins turgid,
and the whole hand full of blood, I ask, Whence is
this? Does the blood accumulate below the ligature
coming through the veins, or through the arteries,
or passing by certain secret pores? Through the
veins it cannot come; still less can it come by any
system of invisible pores; it must needs, then, arrive
by the arteries.”
The third position to be proved is
that the veins return the blood to the heart from
all parts of the body. That such is the case might
be inferred from the presence and disposition of the
valves in the veins; for the office of the valves
is by no means explained by the theory that they are
to hinder the blood from flowing into inferior parts
by gravitation, since the valves do not always look
upwards, but always towards the trunks of the veins,
invariably towards the seat of the heart. The
action of the valves is then demonstrated experimentally
on the arm bound as for blood-letting. The point
of a finger being kept on a vein, the blood from the
space above may be streaked upwards till it passes
the valve, when that portion of the vein between the
valve and the point of pressure will not only be emptied
of its contents, but will remain empty as long as
the pressure is continued. If the pressure be
now removed, the empty part of the vein will fill instantly
and look as turgid as before.
Other confirmatory evidence is then
added, e.g. the absorption of animal poisons
and of medicines applied externally, the muscular structure
of the heart and the necessary working of its valves.
William Harvey, the illustrious physiologist,
anatomist, and physician, to whom this discovery is
due, was the eldest son of a Kentish yeoman, and was
born in April, 1578. At the age of ten he entered
the Canterbury Grammar School, where he appears to
have remained for some years. At sixteen he passed
to Caius-Gonvil College, Cambridge, and three years
afterwards took his B.A. degree and quitted the university.
Like most students of medicine of that day, he found
it necessary to seek the principal part of his professional
education abroad. He travelled to Italy, selected
Padua as his place of study, and there continued to
reside for four years, having as one of his teachers
the famous Fabricius of Aquapendente. On his
return to England, in 1602, he took his doctor’s
degree at Cambridge, and entered on the practice of
his profession.
In 1604 he joined the College of Physicians,
and three years later was elected a Fellow of that
learned body. Two years afterwards he applied
for the post of physician to St. Bartholomew’s
Hospital; and his application being supported by letters
of recommendation to the governor, from the king and
from the president of the College of Physicians, he
was duly elected to the office in the same year, as
soon as a vacancy occurred.
In 1615, when thirty-seven years of
age, Harvey was chosen to deliver the lectures on
surgery and anatomy to the College of Physicians, and
it is possible that at this time he gave an exposition
of his views on the circulation. He continued
to lecture on the same subject for many years afterwards,
although he did not publish his views until 1628, when
they appeared in the work “De Motu Cordis.”
Some few years after his appointment
as lecturer to the college, he was chosen one of the
physicians extraordinary to King James I., and about
five or six years after the accession of Charles I.
he became physician in ordinary to that unfortunate
monarch. The physiologist’s investigations
seem to have interested King Charles, for he had several
exhibitions made of the punctum saliens in the
embryo chick, and also witnessed dissections
from time to time.
When, in 1630, the young Duke of Lennox
made a journey on the Continent, Harvey was chosen
to travel with him, and probably remained abroad about
two years. During this time Harvey most likely
visited Venice. Of this tour the doctor speaks
in the following terms in a letter written at the
time: “I can only complayne that by the
waye we could scarce see a dogg, crow, kite, raven,
or any bird or any thing to anatomise; only sum few
miserable poeple the reliques of the war and the
plauge, where famine had made anatomies before
I came.”
Six years after this, in April, 1636,
he accompanied the Earl of Arundel in his embassy
to the emperor. Having to visit the principal
cities of Germany, he was thus afforded an opportunity
of meeting the leading biologists of the time, and
at Nuremberg he probably met Caspar Hoffmann, and
made that public demonstration of the circulation of
the blood which he had promised in his letter dated
from that city, and which convinced every one present
except Hoffmann himself. Hollar, the artist,
informs us that Harvey’s enthusiasm in his search
for specimens often led him into danger, and caused
grave anxiety to the Earl of Arundel. “For
he would still be making of excursions into the woods,
making observations of strange trees, plants, earths,
etc., and sometimes like to be lost; so that
my lord ambassador would be really angry with him,
for there was not only danger of wild beasts, but of
thieves.”
Soon after his return to England,
as court physician, his movements became seriously
restricted by the fortunes of the king. Aubrey
says, “When King Charles I., by reason of the
tumults, left London, Harvey attended him, and was
at the fight of Edgehill with him; and during the
fight the Prince and the Duke of York were committed
to his care. He told me that he withdrew with
them under a hedge, and tooke out of his pockett a
booke and read; but he had not read very long before
a bullet of a great gun grazed on the ground neare
him, which made him remove his station.... I
first sawe him at Oxford, 1642, after Edgehill fight,
but was then too young to be acquainted with so great
a doctor. I remember he came severall times to
our Coll. (Trin.) to George Bathurst, B.D., who
had a hen to hatch egges in his chamber, which they
dayly opened to see the progress and way of generation.”
In 1645, Charles, after the execution
of Archbishop Laud, took upon himself the functions
of visitor of Merton College, and having removed Sir
Nathaniel Brent from the office of warden for having
joined “the Rebells now in armes against”
him, he directed the Fellows to take the necessary
steps for the election of a successor. This course
consisted in giving in three names to the visitor,
in order that one of the three (the one named first,
probably) should be appointed. Harvey was so named
by five out of the seven Fellows voting, and was accordingly
duly elected. A couple of days after his admission
he summoned the Fellows into the hall and made a speech
to them, in which he pointed out that it was likely
enough that some of his predecessors had sought the
office in order to enrich themselves, but that his
intentions were quite of another kind, wishing as
he did to increase the wealth and prosperity of the
college; and he finished by exhorting them to cherish
mutual concord and amity. After the surrender
of Oxford, July, 1646, Harvey retired from the court.
He was in his sixty-ninth year, and doubtless found
the hardships and inconveniences which the miserable
war entailed far from conducive to health. The
rest and seclusion to be had at the residence of one
or other of his brothers offered him the much-needed
opportunity of renewing his inquiries into the subject
of generation, and it is of this time that Dr. Ent
speaks in the preface to the published work on that
subject which appeared in 1651. “Harassed
with anxious and in the end not much availing cares,
about Christmas last, I sought to rid my spirit of
the cloud that oppressed it, by a visit to that great
man, the chief honour and ornament of our college,
Dr. William Harvey, then dwelling not far from the
city. I found him, Democritus-like, busy with
the study of natural things, his countenance cheerful,
his mind serene, embracing all within its sphere.
I forthwith saluted him, and asked if all were well
with him. ‘How can it,’ said he, ’whilst
the Commonwealth is full of distractions, and I myself
am still in the open sea? And truly,’ he
continued, ’did I not find solace in my studies,
and a balm for my spirit in the memory of my observations
of former years, I should feel little desire for longer
life. But so it has been, that this life of obscurity,
this vacation from public business, which causes tedium
and disgust to so many, has proved a sovereign remedy
to me.’”
Harvey died in June, 1657. Aubrey,
his contemporary, says, “On the morning of his
death, about ten o’clock, he went to speake,
and found he had the dead palsey in his tongue; then
he sawe what was to become of him, he knew there was
then no hopes of his recovery, so presently sends
for his young nephews to come up to him, to whom he
gives one his watch, to another another remembrance,
etc.; made sign to Sambroke his Apothecary to
lett him blood in the tongue, which did little or no
good, and so he ended his dayes.... The palsey
did give him an easie passeport.... He lies
buried in a vault at Hempsted in Essex, which his
brother Eliab Harvey built; he is lapt in lead, and
on his brest, in great letters, ‘Dr. William
Harvey.’ I was at his Funerall, and helpt
to carry him into the vault.”
The publication of Harvey’s
views on the movement of the blood excited great surprise
and opposition. The theory of a complete circulation
was at any rate novel, but novelty was far from being
a recommendation in those days. According to
Aubrey, the author was thought to be crackbrained,
and lost much of his practice in consequence.
He himself complains that contumelious epithets were
levelled at the doctrine and its author. It was
not until after many years had elapsed, and the facts
had become familiar, that men were struck with the
simplicity of the theory, and tried to prove that
the idea was not new after all, and that it was to
be found in Hippocrates, or in Galen, or in Servetus,
or in Caesalpinus anywhere, in fact, except
where alone it existed, namely, in the work, “De
Motu Cordis et Sanguinis.”
No one seems to have denied, while Harvey lived, that
he was the discoverer of the circulation of the blood;
indeed, Hobbes of Malmesbury, his contemporary, said
of him, “He is the only man, perhaps, that ever
lived to see his own doctrine established in his lifetime.”
In one important respect Harvey’s
account of the circulation was incomplete. He
knew nothing of the vessels which we now speak of as
capillaries. Writing to Paul Marquard Slegel,
of Hamburg, in 1651, he says, “When I perceived
that the blood is transferred from the veins into
the arteries through the medium of the heart, by a
grand mechanism and exquisite apparatus of valves,
I judged that in like manner, wherever transudation
does not take place through the pores of the flesh,
the blood is returned from the arteries to the veins,
not without some other admirable artifice” (non
sine artificio quodam admirabili). It was
this artificium admirabile of which Harvey was
unable to give a description. On account of the
minuteness of their structure, the capillaries were
beyond his sight, aided as it was by a magnifying
glass merely. He indeed demonstrated physiologically
the existence of some such passages; but it remained
for a later observer, with improved appliances, to
verify the fact. This was done by Malpighi in
1661, who saw in the lung of a frog, which was so mounted
in a frame as to be viewed by transmitted light, the
network of capillaries which connect the last ramifications
of the arteries with the radicles of the veins.
Harvey rightly denied that the arteries
possessed any pulsific power of their own, and maintained
that their pulse is owing solely to the sudden distension
of their walls by the blood thrown into them at each
contraction of the ventricles. But the remission
which succeeds the pulse was regarded by him as caused
simply by collapse of the walls of the arteries due
to elastic reaction. Knowing nothing of the muscular
coat of the arteries, he was unaware of the fact that
the elastic reaction of the arteries, after their
distension, is aided by the tonic contractility of
their walls; the two forces, physical and vital, acting
in concert with each other the former converting
the intermittent flow from the heart into an even
stream in the capillaries and veins; the latter, through
the vaso-motor system, regulating the flow
of blood to particular parts in order to meet changing
requirements.
It is somewhat surprising to find
that such an accurate observer as Harvey should have
failed to recognize the significance and importance
of the system of lacteal vessels. But such was
the case. Eustachius, in the sixteenth century,
had discovered the thoracic duct in the horse, although
he seems to have thought that it was peculiar to that
animal. Aselli, while dissecting the body
of a dog in 1622, accidentally discovered the lacteals,
and thought at first that they were nerves; but upon
puncturing one of them, and seeing the milky fluid
which escaped, found them to be vessels. He,
however, failed to trace them to the thoracic duct,
and believed them to terminate in the liver. Pecquet
of Dieppe followed them from the intestines to the
mesenteric glands, and from these into a common sac
or reservoir, which he designated receptaculum
chyli, and thence to their entry by a single slender
conduit into the venous system at the junction of the
jugular and subclavian veins. The existence of
the lacteals had not entirely escaped Harvey, however.
He had himself noticed them in the course of his dissections
before Aselli’s book was published, but “for
various reasons” could not bring himself to
believe that they contained chyle. The smallness
of the thoracic duct seemed to him a difficulty, and
as it was a demonstrated fact that the gastric veins
were largely absorptive, the lacteals appeared to
him superfluous. He is not “obstinately
wedded to his own opinion,” and does not doubt
“but that many things, now hidden in the well
of Democritus, will by-and-by be drawn up into day
by the ceaseless industry of a coming age.”
Late in the author’s life, as
we have seen, the work on the “Generation of
Animals” appeared; but neither physiological
nor microscopical science was sufficiently advanced
to admit of the production of an enduring work on
a subject necessarily so abstruse as that of generation.
It was impossible, however, for so shrewd and able
an investigator as Harvey to work at a subject even
as difficult as this without leaving the impress of
his original genius. He first announced the general
truth, “Omne animal ex ovo,”
and clearly proved that the essential part of the
egg, that in which the reproductive processes begin,
was not the chalazae, but the cicatricula.
This Fabricius had looked upon as a blemish, a scar
left by a broken peduncle. Harvey described this
little cicatricula as expanding under the influence
of incubation into a wider structure, which he called
the eye of the egg, and at the same time separating
into a clear and transparent part, in which later
on, according to him, there appeared, as the first
rudiment of the embryo, the heart, or punctum saliens,
together with the blood-vessels. He was clearly
of opinion that the embryo arose by successive formation
of parts out of the homogeneous and nearly liquid
mass. This was the doctrine of epigenesis, which,
notwithstanding its temporary overthrow by the erroneous
theory of evolution, is, with modifications, the
doctrine now held.
Of Harvey’s scholarship and
culture we are not left in ignorance. Bishop
Pearson, writing about seven years after the doctor’s
death, and Aubrey have told us of his appreciation
of the works of Aristotle, and in his own writings
he refers more frequently to the Stagirite than to
any other individual. Sir William Temple has
also put it on record that the famous Dr. Harvey was
a great admirer of Virgil, whose works were frequently
in his hands. His store of individual knowledge
must have been great; and he seems never to have flagged
in his anxiety to learn more. He made himself
master of Oughtred’s “Clavis Mathematica”
in his old age, according to Aubrey, who found him
“perusing it and working problems not long before
he dyed.”
Nor should it be forgotten that this
illustrious physiologist and scholar was also the
first English comparative anatomist. Of his knowledge
of the lower animals he makes frequent use, and he
says (in his work on the heart), “Had anatomists
only been as conversant with the dissection of the
lower animals as they are with that of the human body,
many matters that have hitherto kept them in a perplexity
of doubt, would, in my opinion, have met them freed
from every kind of difficulty.” Aubrey
says that Harvey often told him “that of all
the losses he sustained, no grief was so crucifying
to him as the loss of his papers (containing notes
of his dissections of the frog, toad, and other
animals), which, together with his goods in his lodgings
at Whitehall, were plundered at the beginning of the
rebellion.”