work to the functions of the organs which he describes. Where he differs
from Galen on these matters he does so apologetically. He follows him in
regarding the heart as the seat of the emotions and passions--the
hottest of all the viscera and source of heat of the whole body;
although he does not, as Aristotle did, look upon the heart as giving
rise to the nerves. He considers the heart to be in ceaseless motion,
alternately dilating and contracting, but the diastole is in his opinion
the influential act of the organ. He knows that eminences or projections
are present in the veins, and indeed speaks of them as being analogous
to the valves of the heart, but he denies to them the office of valves.
To him the motion of the blood was of a to-and-fro kind, and valves in
the veins acting as such would have interfered with anything of the
sort. He expresses clearly the idea, that was entertained in the old
physiology, of the attractions exerted by the various parts of the body
for the blood; and especially that of the veins and heart for the blood
itself. "The right sinus of the heart," he says, "attracts blood from
the vena cava, and the left attracts air from the lungs through the
_arteria venalis_ (pulmonary vein), the blood itself being attracted by
the veins in general, the vital spirit by the arteries." Again, he
speaks of the blood filtering through the septum between the ventricles
as if through a sieve, although he knows perfectly well from his
dissection that the septum is quite impervious.
It will thus be seen that the physiological teaching of Galen was left
undisturbed by Vesalius.
FOOTNOTES:
[19] See Professor Morley's article on "Anatomy in Long Clothes," in
_Fraser's Magazine_, 1853, from which most of the facts in this sketch
have been taken.
HARVEY.
_HARVEY._
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 Harvey's 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
Cæsalpinus--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."