|
"Toward the end of the fourth day and the beginning of the
fifth
the sanguineous point is already increased in size and is
seen
to be turned into a small and very delicate vesicle
containing
blood within itself; which blood it drives out at
every
contraction, and receives afresh when its diastole takes
place.
"Up to this stage I have found it impossible to
discriminate
between the vessels; for the arteries are not to be
distinguished from the veins either by their coats or by
the pulse; and
so I think it best to style all the vessels,
indiscriminately, veins or,
with Aristotle,[186] venous
canals....[187]
"On the sixth
day ... the parenchyma of the heart grows on to
the pulsating vesicle;
and shortly afterward the rudiments of
the liver and of the lungs are
discernible."[188]
It is clear that Harvey's hens did not very often take
such
well-timed steps against Aristotle; for in another passage of
his
treatise on generation, in summing up its events and their order,
he
frankly states the difficulties which render uncertain the
question of
priority between the blood and the heart. He speaks of
"the first generated
and generative part; that is to say, the blood
together with its receptacles
or, if you prefer, the heart with its
veins."[189] A few lines further on he
says:--
"In the generation of this first part (which is
accomplished
in the egg on the fourth day) although I have not been able
to
observe any order, because all portions of the part aforesaid
(namely, the blood, the veins and the pulsating vesicle) appear
at the
same time; nevertheless, my belief would be, as I have
said, that the
blood is present before the pulse; and that,
therefore, in obedience to
a law of nature the blood is prior to
its receptacles, that is, to the
veins."[190]
In Harvey's first publication, of 1628, we have
read:--
"If you turn to the formation of the chick in the egg, the
first
thing to exist therein, as I have said, is a mere vesicle,
or
auricle, or pulsating drop of blood. Afterward, when growth
has
gone on, the heart is completed."[191]
In his last
publication, of 1651, we have read:--
"So far as can be discerned by
accurate inspection, the blood
is made before the leaping point is
formed, and the blood
is endowed with vital heat before it is set in
motion by
pulsation; and further, as pulsation is begun in and by
the
blood, so at last it ends in the blood at the final instant
of
death."[192]
Harvey's own words in the foregoing two passages
effectively sum up
both the nature of his doctrine that the blood is the
first part of
the body to live, and the nature of his evidence. But the words
of
the second passage foreshadow a closely related doctrine, advanced
and
held by him on the evidence of observation, viz.: that the
blood, being the
first part to live, is also the last part of the
body to die. That the first
part to live is always the last to die,
is a doctrine set forth by Aristotle.
This, Harvey seems to accept
without question and to apply upon proper
evidence to the blood; as
he accepts and warmly upholds the ancient master's
doctrine that
there is a primacy of the body. The results of observation
have
forced Harvey to transfer this primacy from the heart to the
blood,
but it is the Aristotelian primacy still. Presently he shall show
us
that the blood is not only the first part to live, but the last to
die.
Before he does so, however, let Aristotle speak for himself,
saying
briefly:--
"The point[193] of origin [of the rest of the body] is
the
first thing generated. The point of origin in the animals
which
possess blood is the heart; in the rest, the analogue
thereof,
as I have often said. Moreover, the fact that the heart is
the
first thing generated is evident, not only to the senses,
but
from its death.[194] For therein life ceases the last; and
in
all cases the last generated is the first to make an end, the
first generated, the last to make an end; nature, as it were,
doubling
back and returning upon her point of origin whence
she came.[195] For
generation is the change from not being to
being; destruction is the
reverse change, from being to not
being."[196]
Aristotle does not
tell us why "in all cases ... the first
generated" is "the last to make an
end," and _vice versa_. Let
it suffice that Harvey accepts this sweeping
doctrine. Now let
him complete his evidence in favor of the primacy of the
blood by
showing that the blood is not only the first part to live and
to
live tenaciously, but the last part to die.
In a passage of the
treatise On the Motion of the Heart and Blood,
we have already read Harvey's
promise to publish observations
"on the formation of the fœtus,
where numerous problems of
the following order can find a place: Why
should this part be
made or perfected earlier, that later? As regards
the dominance
of the members: Which part is the cause of the other?
There are
very many problems connected with the heart, such as: Why
should
it be the first thing (as Aristotle says in his third book
On
the Parts of Animals)[127] to acquire consistency, and be
seen
possessed of life, motion, and sensation, before anything
has
been perfected in the rest of the body? And in like manner
regarding the blood: Why is it before all, and how possessed
of the
beginnings[128] of life and of the animal, and of the
craving to move
and be impelled hither and thither, to which end
the heart would seem to
have been made?"[129]
That Harvey should have printed this passage in
1628, in the same
work with his repeated eulogies of the Aristotelian heart,
shows
that the idea of the possible primacy of the blood must have been
in
his mind early. It was, indeed, so from the jotting down of
his private notes
of 1616, to the publication of the Exercises to
Riolanus in 1649 and the
treatise On Generation in 1651. The same
mental attitude is revealed, perhaps
more strongly, in the following
passage of an earlier chapter of Harvey's
treatise of 1628. Here
we come upon the thought that it may be the blood, and
neither
ventricle nor auricle, which is the last to die. Harvey
says:--
"Besides this, however, I have occasionally observed,
after
the heart and even its right auricle[197] had ceased their
pulsations as though in the act of dying, that an obscure
motion and
flow and a sort of palpitation manifestly remained
in the blood itself
contained in the right auricle, so long,
that is, as the blood appeared
to be imbued with heat and
spirits. Something of the sort is very
plainly to be seen at
the beginning of the generation of an animal, in
the hen's egg
within the first seven days of incubation. There is
present,
first and before all else, a drop of blood which palpitates
(as
Aristotle also noted); from which, when growth has taken
place
and the chick has been formed to some extent, the auricles
of
the heart are made; and in these, which pulsate perpetually,
life inheres....
"Whoever, therefore, shall choose to investigate
more closely
will say that the heart is not the first to live and the
last to
die, but that the auricles, and the part which answers
thereto
in serpents, fishes, and such animals, are alive sooner than
the
heart itself and also die later than the heart. Whether even
earlier the blood itself, or the spirit, have not an obscure
palpitation
of its own, which it has seemed to me to retain
after death, may well be
questioned; and whether we should not
speak of life as beginning with
palpitation."[198]
It is plain that fibrillar contractions of cardiac
muscle misled
Harvey into thinking and writing of "an obscure motion and
flow,"
of "an obscure palpitation," of the blood itself within the
dying
auricle. It is plain that when he wrote his most famous treatise
he
was loath, even under Aristotle's leadership, to reach out so
far
beyond the evidence of the senses as to attribute the palpitation
of
the visible drop of blood in the very early embryo to anything
but the hot
blood itself. Later, in his treatise On Generation,
he published a passage
which in some ways runs parallel with the
foregoing. In the earlier passage
the results of observation are
brought forward as food for thought; in the
later one, as proofs of
a theory, fully, clearly, and emphatically stated by
a thinker who
is near the end of life and is imparting his final judgment.
This
later passage is as follows:--
"In whatsoever part of the
body heat and motion have their
beginning, in that same part life also
first arises and therein
is extinguished last; nor may it be doubted
that there, too,
life has its innermost home, that there the soul itself
has
fixed its seat.
"The life then inheres in the blood (as
we read also in Holy
Writ[199]), because therein the life and the soul
are manifest
first and fail last. For, as I have said, in the dissection
of
living animals I have found repeatedly that, though the
animal
be dying and breathe no longer, nevertheless, the heart
pulsates
for some time and keeps the life in it. Moreover, when the
heart
is quieted you may see movement surviving in the auricles,
and
latest in the right auricle; and at length all pulsation
ceasing
there, you may find in the blood itself a kind of undulation
and
obscure agitation or palpitation, the last indication of
life.
And anyone can perceive that the blood retains in itself to
the
last the heat which is the author of pulsation and life; if
this
heat is once wholly extinguished and the blood now is blood
no more, but cruor, so there is left no hope of a return to
life again.
Nevertheless, after all pulsation has disappeared,
both in the egg, as I
have said, and in dying animals, if you
will make a gentle warm
application, in the former case to the
leaping point, in the latter to
the right auricle of the heart,
you shall see movement, pulsation, and
life, renewed immediately
by the blood; provided it have not utterly
lost all its innate
heat and vital spirits."[200]
How readily
heat from without can revive the cool leaping point, is
strikingly set forth
by Harvey in another chapter of this treatise
On Generation. He
says:--
"Moreover, if an egg be exposed too long to a colder
atmosphere,
its leaping point pulsates less often and stirs more
languidly;
but if a warm finger be applied to it, or any other bland
source
of warmth, straightway it recovers strength and vigor.
Indeed,
when such a point has become gradually weak and though full
of
blood ceases to move at all and gives no sign of life,
seeming
utterly to have succumbed to death, if my lukewarm finger
be
placed over it for the space of twenty pulsations of my
artery,
behold! the little heart revives once more, becomes erect,
and
renews its pristine dance as though come back from Hades.
This
I myself and others, too, have brought about again and again
by
means of gentle warmth of any kind, such as that of a fire or
of
tepid water; thus at our pleasure being able to give over the
poor little soul to death, or call it back to the light."[201]
As in the
embryo the leaping point may be revived by external
warmth, so may the heart
in the full-grown bird. In his treatise of
1628 Harvey says:--
"In the pigeon, at any rate, at an actual experiment, after the
heart
had wholly ceased to move and even the auricles had left
off moving, I
placed my finger, wetted with saliva and warm,
upon the heart and kept
it there for a while; as the result of
which fomentation the heart, as
though restored to strength and
life again, and its auricles with it,
were seen to move and
contract and relax themselves and, as it were, to
be recalled
from death."[202]
In his treatise On Generation,
Harvey confirms the doctrine of the
primacy of the blood by citing
observations made upon sluggish or
hibernating animals and also certain
morbid phenomena in man, as
follows:--
"This, too, clearly
follows from many observations; especially
the cases of certain animals
which possess blood yet live a long
time without a pulse; and of some
which lie hidden the whole
winter and, nevertheless, continue alive,
although meanwhile all
movement of the heart has ceased and their lungs
enjoy a rest
from breathing, like people who lie half dead and pulseless
in
syncope or faintness or hysterical affections."[203]
So Harvey
convinced himself, by observation, that the first part of
the developing
embryo to appear is the blood of the "sanguineous
lines"; after this the
blood which seems to palpitate of itself at
the leaping point, which later
develops into a pulsating vesicle
wherein blood is contained within a
contractile wall; to this being
superadded still later the contractile
parenchyma of the heart.
Also, by observation, he convinced himself that in a
dying animal
the blood within the right auricle may palpitate of itself after
the
palpitations due to contractions of the auricular wall have
ceased.
Thus was Harvey led to believe that the blood and not the heart
is
the first part to live and the last to die, the principal part of
the
body, the generator of the heart and of all the rest. In spite
of his appeal
to observation, his impressive primacy of the blood is
now as completely
forgotten in its turn as is Aristotle's impressive
primacy of the heart,
which Harvey felt called upon to supersede.
Naturally in this matter the
great discoverer used true methods of
investigation; and doubtless his
imperfect conclusions were due in
large part to the weakness of his
magnifying glasses and to the
deficient technique of his day. Harvey said of
himself, speaking
generally, that he trusted much to the plain use of his
senses.[204]
That he did so, was well for him and for all mankind; yet
because of
this very trust he did not always escape the pitfalls dug by what
we
now call "naked-eye" appearances.
CHAPTER
VII
THE CAUSE OF THE HEART-BEAT
The primacy of the blood was
no isolated fact for Harvey, but one
linked with the very existence of the
circulation. This primacy
depended largely upon the blood being the primal
abode of the innate
heat. Palpitation produced by the innate heat in the
blood itself,
he held to be the first sign of life in the embryo and the last
sign
of life in the dying creature; and a swelling produced by the
innate
heat, he held to take place throughout life, localized in the
blood
just outside of the entrance to the heart. This local swelling
of
the blood was, to him, the exciting cause of the heart-beat
and,
therefore, of the circulation. We have heard him deny that the
blood
possesses motion "as the gift of the heart."[205] We can now
grasp the
probable meaning of this denial. He would not have been
illogical had he said
also that the heart possesses motion as the
gift of the blood. This view of
the cause of the heart-beat was
first set forth by Harvey in 1649 in the
Exercises to Riolanus,
and in immediate connection with declarations in favor
of the
primacy of the blood, which also was first formally advocated
in
those Exercises. As we know, the question of this primacy had
given
Harvey food for thought long before. But his view of the cause
of
the heart-beat is not to be found in his lecture notes, nor in
the
treatise of 1628, and may well have been a later outgrowth from
the
larger doctrine of the primacy of the blood.
Let us now turn to
the Exercises and to Harvey's own account of the
cause of the heart-beat. The
first passage to be quoted begins with
a few sentences which have been
introduced previously, but which
form a necessary cue for the statement we
are to study. Harvey says
to Riolanus:--
"For the present I will
only say and set forth without
demonstration--by good leave of the
learned and with due respect
to the ancients--that the heart, as the
beginning, author,
source, and origin of everything in the body and the
first
cause of life, should be held to include the veins and all
the arteries and also the contained blood; just as the brain,
including
all its nerves and sensory organs and spinal marrow,
is the one adequate
organ of sensation, as the phrase is. If by
the word 'heart,' however,
only the body of the heart be meant
with its ventricles and auricles, I
do not believe that it is
the manufacturer of the blood; nor that the
blood possesses
vigor, faculty, reason,[168] motion, or heat, as the
gift of the
heart. Moreover, I judge the cause of diastole and expansion
not
to be the same as that of systole and contraction, either in
the
arteries, or in the auricles or the ventricles of the heart;
but that part of the pulse which is called diastole has another
cause,
different from the systole, and always and everywhere
must precede every
systole; I judge the first cause of expansion
to be the innate heat and
expansion to occur first in the
blood itself, gradually thinned and
swelling up like matters
in fermentation, and to be extinguished last in
the same; and
I accept Aristotle's parallel with pottage or milk with
this
proviso, that the rising or falling of the blood is not
brought
about by vapors, or exhalations, or spirits, excited into
some
vaporous or aerial form, and is caused, not by an external
agent, but by an internal principle, and is regulated by nature.
"Nor is the heart (like a hot kettle), as some imagine, the
origin of
the heat and of the blood in the same sense as a hot
coal or a
fire-place. The blood rather imparts heat to the
heart, as to all other
parts, than receives heat from it, for
the blood is, of all things
within the body, the hottest; and
so the heart is provided with coronary
arteries and veins for
the same purpose as that of the arteries and
veins of other
parts, viz.: to secure an influx of heat which shall
foster and
preserve. Hence it is to use convertible terms to say that
all
the hotter parts contain more blood and that the richer they
are in blood, the hotter they are. It is in this sense that the
heart,
so remarkable for its cavities, should be reckoned a
workshop, source,
perpetual fire-place; it is like a hot kettle
by virtue, not of its
body, but of its contained blood, in the
same sense in which the liver,
the spleen, the lungs, and other
parts are reckoned hot; because they
contain many veins or
vessels containing blood. In this way also I
maintain that the
native heat, or innate warmth, being the common
instrument of
all the functions, is likewise the prime efficient cause
of the
pulse. This I do not now assert positively, but only propose
as
a thesis. Whatever may be brought forward to the contrary by
learned and upright men without scurrilous language, clamor, or
contumely, I shall be glad to know, and whoever shall do that
will earn
my gratitude."[206]
Harvey has thus transferred to the blood the primacy
of the body,
making the blood in place of the Aristotelian heart the primal
abode
of the innate heat, "the common instrument of all the
functions."
Nevertheless, the blood of the Harveian circulation cannot
perform
the duties of the primacy without the aid of Aristotle.
If we
turn from the Exercises to the treatise On Generation,
published about two
years later, we find the author saying:--
"The primacy of the blood
is evident from this also, that
the pulse has its origin in the blood.
For since a pulsation
consists of two parts, to wit: an expansion and a
contraction,
or a diastole and systole, and since the prior of
these
movements is the expansion, it is plain that this action is
due
to the blood, but that the contraction is set a-going in the
egg by the pulsating vesicle, as by the heart in the chick, by
means of
its own fibres as though by an instrument devised for
that purpose. It
is certain also that the aforesaid vesicle
and, at a later time, the
cardiac auricle from which pulsation
starts, is excited by the blood,
which expands to the motion
which constricts. The diastole, I say, is
produced by the blood
which swells up as if with interior spirits; and
so Aristotle's
opinion as to the heart's pulsation--namely, that it is
produced
after the manner of ebullition--is in some measure true. For
the
same thing which we see every day in milk heated over the
fire
and in the fermentation of our beer, comes into play also in
the
pulsation of the heart, in which the blood swells as from
some
fermentation, is expanded, and subsides; and what is
brought
about in the cases aforesaid by accident and by an
external
agent, to wit, by adventitious heat from somewhere, is
effected
in the blood by the internal heat or innate spirits, and
is
also regulated by the soul in conformity to nature, and is
kept
up for the health of living things. Pulsation, therefore,
is
accomplished by a double agency: that is to say, the
expansion
or dilatation is accomplished by the blood, but the
contraction
or systole is accomplished in the egg by the membrane of
the
vesicle, in the fœtus after birth by the auricles and
ventricles of the heart; and these alternate and mutually
associated
efforts once begun, the blood is impelled through the
whole body, and
thus the life of animals is perpetuated."[207]
Nearly two thousand years
before Harvey's time Aristotle had said:--
"The volume of
leaven[208] changes from small to great,
by its more solid part becoming
liquefied and its liquid,
vaporized.[209] This is brought about in
animals by the nature
of the psychical heat, but in the case of leaven
by the heat of
the blended juices."[210]
Moreover, Aristotle, as
Harvey says, had likened to
"ebullition"[211] what Aristotle himself
described as "the pulsation
which occurs at the heart, at which the heart is
always to be seen
incessantly at work." "For," says Aristotle, "ebullition
takes place
when liquid is vaporized[212] by heat; for it rises up owing to
its
bulk becoming greater."[213] He continues:--
"In the heart
the swelling up from heat of the liquid which
is always arriving from
the food produces pulsation, for the
swelling rises against the outer
tunic[214] of the heart; and
this process is always and incessantly
going on, for the liquid
is always and incessantly flowing in, out of
which the nature
of the blood arises; for the blood is first worked up
in the
heart. The thing is plain in generation from the beginning;
for
before the vessels have been marked out the heart is to be
seen
containing blood. Hence, too, it pulsates more in the young
than
in the old; for the vapor[215] arises more abundantly in
the
young.
"All the vessels also pulsate and do so
simultaneously one with
another, because they are dependent upon the
heart.[216] This
is always moving, so that they, too, are always moving,
and
simultaneously one with another, when[217] the heart moves.
Leaping [of the heart],[218] then, is the reaction which takes
place
against the condensation produced by cold, and pulsation
is the
vaporization[219] of heated liquid."[220]
In another treatise Aristotle
says: "In all animals the blood
pulsates in the vessels everywhere at the
same time."[221] It
is interesting, in a negative way, that his sweeping and
faulty
references to the pulsation of the vessels put into words
no
physiological idea except the vague one of "dependence" on the
heart.
One may be tempted to see in the seething of the heart's blood
the
source of some of those spirits within the body elsewhere than in
and
about the heart, of which one gets brief ill-defined glimpses
here and there
in the genuine works of Aristotle. But no words of
his can be adduced to
confirm such a conjecture.
Evidently, however, the seething of the
nascent blood suffices, in
Aristotle's eyes, to explain both the phases of
the heart-beat;
for both the rising and the falling of the wall of the hot
central
laboratory of the blood are movements as passive apparently
as
those of the lid of a boiling pot. One may be excused for wondering
at
the crudity of such a conception; nor is one's wonder lessened by
recalling
that elsewhere in Aristotle's works he places at the heart
the central origin
of the bodily movements. But when it is recalled,
as well, that Aristotle was
totally ignorant of the function of
muscle and, therefore, even of the mode
of working of the limbs, his
doctrine of the heart-beat may seem less
amazing.
There are indications that the function of muscle, though
unknown to
Aristotle, was known not long after his time,[222] and in
Galen's
time that function was entirely familiar, he styling the
muscles
"the organs of voluntary movement," and calling their
contraction
their "systole," a term which has survived only in connection
with
the heart and arteries.[223] For Harvey, born more than
thirteen
centuries after Galen's death, the function of muscle was a
portion
of ancient knowledge; and in his treatise On the Motion of
the
Heart and Blood, he expressly states that the heart, including
the
auricles, is muscular both in structure and in function. The
opinions of
Harvey's day rendered these statements by no means
superfluous.[224]
Naturally, therefore, in accepting the aid of the
Aristotelian seething of
the blood in connection with the heart-beat
Harvey utilized only the force of
expansion thus generated, and
obtained from muscle the force of contraction
which he required.
Indeed, the conception of the auricles and ventricles as
muscular
force-pumps was fundamental to his doctrine of the
circulation.
Moreover, we have found Harvey careful to limit and mitigate
the
expansion of the blood, he saying to Riolanus:--
"I accept
Aristotle's parallel with pottage or milk with this
proviso, that the
rising or falling of the blood is not brought
about by vapors, or
exhalations, or spirits, excited into some
vaporous or aerial form, and
is caused, not by an external
agent, but by an internal principle, and
is regulated by
nature."[225]
Long before, indeed, he had jotted
down a terse statement among
his lecture notes which is fatal to any extreme
development of the
Aristotelian idea. In dealing with the action of the heart
he had
written:--
"To what end? Aristotle: To none, but a passive
process, as in
boiling pottage. But when wounded it gives out not wind,
but
blood."[226]
Harvey, therefore, could do no less than
criticize adversely his
famous contemporary, the philosopher Descartes, for
accepting in
its entirety Aristotle's doctrine of the heart-beat. Referring
to
Descartes he says:--
"Nor in the matter of the pulse am I
satisfied with the
efficient cause thereof which he, following
Aristotle, has
laid down as the same at the systole as at the diastole,
to
wit: an effervescence of the blood like that produced in
boiling. For the movements aforesaid are sudden strokes and
swift beats;
while in fermentation or ebullition nothing rises
up and collapses thus,
as it were in the twinkling of an eye,
but there is a slow swelling with
a sufficient subsidence. By
means of dissection, moreover, one can
discern for oneself that
the ventricles of the heart are expanded as
well as filled by
the constriction of the auricles and are increased in
size
proportionately, according as they are filled more or less;
and that the expansion of the heart is a movement of a certain
violence,
produced by impulsion, not by attraction[227] of some
sort."[228]
In a letter written four years after the publication of
the
Exercises to Riolanus and two years after that of the treatise
On
Generation, Harvey sets forth anew, with admirable clearness
and
brevity, his doctrine as to the nature and cause of the systole
of the
ventricles. In this he stands upon purely modern ground as
an observer, and
his words are free from all Aristotelian tinge.
Referring to another
physiologist he says:--
"I could wish, however, that he had observed
this one thing,
namely, that the motion which the heart enjoys is of a
threefold
kind, to wit: a systole, in which the heart contracts
itself
and drives out the blood contained in it; and then a
certain
relaxation, of a character contrary to the foregoing
motion,
a relaxation in which the fibres of the heart which make
for
motion are slackened. The two motions aforesaid are inherent
in the very substance of the heart, just as in all other
muscles.
Finally, there takes place a diastole, in which the
heart is expanded by
blood impelled into its ventricles out of
the auricles; and the heart is
incited to its own contraction
by this filling and expansion of the
ventricles; and the
motion aforesaid always precedes the systole, which
follows at
once."[229]
Harvey materially clarifies his doctrine
of the nature and cause of
the heart-beat in the following admirable summary.
In the second
Exercise to Riolanus he says:--
"Since I see that
many are embarrassed and doubt the
circulation, and that some attack it,
because they have not
understood me thoroughly; for their sake I will
recapitulate
briefly what I meant to say in my little book on the motion
of
the heart and blood. The blood contained in the veins, where
its deeps are, as it were, where it is most abundant, that is,
in the
vena cava close to the base of the heart and to the
right auricle,
gradually grows warm and thin by reason of its
own internal heat, and
swells and rises up like matters in
fermentation; whereby the auricle is
dilated, contracts itself
by reason of its own pulsific faculty, and
propels the blood
promptly and frequently into the right ventricle of
the heart.
This, when filled, frees itself of blood at its
succeeding
systole by the impulsion thereof and, as the tricuspid valve
is
a bar to the egress of the blood, drives it where an open
door
is offered, into the arterial vein, and thereby brings
about
the expansion of the latter. The blood within the arterial
vessels cannot now go back in opposition to the sigmoid valve,
while at
the same time the lungs are widened and enlarged and
then narrowed by
inspiration and expiration--and with the lungs
their vessels also--and
offer to the blood aforesaid a path and
transit into the venous artery.
The left auricle accomplishes
its movement, its rhythm, its order [of
events], its function,
at the same time and in the same way as the right
auricle,
and in like manner sends on into the left ventricle out
of
the vessels aforesaid the same blood which the right auricle
had sent on into the right ventricle. As a result the left
ventricle, at
the same time and in the same way as the right,
impels the blood into
the cavity of the aorta and consequently
into all the branches of the
artery, the return of the blood
whence it had come being prevented in
the same way as before by
the barrier of an opposing valve. The arteries
are filled by
this sudden impulsion and, as they cannot unload
themselves as
suddenly, are expanded, receive an impulse, and undergo
their
diastole."[230]
Harvey seems to have attributed more
importance to the auricular
systoles than do the physiologists of to-day, he
making the
ventricles depend very greatly for their charge of blood upon
the
systole of the auricles. This view appears in three passages
already
quoted; and is tersely put by Harvey when he says elsewhere
that
the heart "is dilated by the auricle, contracts of itself";[231]
that
"the auricles are prime movers of the blood."[232] The unduly
high value set
by him upon the auricular systole agrees well
with the polemical vigor with
which Harvey exalted impulsion and
rejected suction,[233] in his general
physiology as well as in
the physiology of the heart. In the heart especially
the force of
suction had played for centuries a part which Harvey rejected
more
completely than the physiologists of to-day feel warranted in
doing.
Again he shall speak for himself, saying tersely:--
"Hence
it is made plain how the blood enters the ventricles;
not by reason of
being drawn in, or of the heart expanding, but
because sent in by the
pulse of the auricles."[234]
"The expansion of the heart," he has told us
already, "is a movement
of a certain violence, produced by impulsion, not by
attraction of
some sort." He says that he maintains these views
"against the commonly received opinion; because neither the
heart nor
anything else can so expand itself that it can draw
anything into itself
in its diastole, unless as a sponge does
which has first been forcibly
compressed and is returning to its
natural state."[235]
But, one
may ask oneself, how does that modified seething in the
vena cava which
produces the diastole of the right auricle produce
the diastole, the
simultaneous diastole, of the left auricle? In his
lecture notes Harvey had
stated, as Columbus had before him, that
the venous artery does not
pulsate--at least, he means, not in the
same sense as the auricle, or
ventricle, or artery.[236] Obviously
regarding the left auricle there could
be available, for Harvey, no
explanation parallel to that of to-day, viz.:
the swift conduction
of a stimulus from point to point of the texture of a
wall which is
common to both auricles. He is careful to state that
corresponding
auricular events occur simultaneously and in the same way in
the
two auricles; and incidentally but frankly he confesses ignorance
of
the reasons why, in the following passage:--
"From those who
declare the causes and reasons of all things
in such a smattering way, I
would be glad to learn how it is
that both eyes move together hither and
thither and in every
direction when they look; how it is that this eye
does not turn
by itself in that direction, that eye in this; likewise,
both
auricles of the heart; and so forth."[237]
The circulation
of the blood, then, according to the final view
of its discoverer, is
maintained by a self-regulating mechanism
worked by causes operating within
the blood itself, the "principal
part" of the body. The systolic muscular
contractions of the walls
of the ventricles are caused by direct mechanical
stimulation (in
modern language) due to diastolic distension by blood of the
relaxed
muscular walls of these chambers. The blood which distends
the
ventricles is driven forcibly into them by the auricular systole,
the
muscular walls of the auricles having been stimulated to
contract by
diastolic distention due likewise to blood.
So much of Harvey's doctrine
of the heart-beat, although not that
of to-day, is very effective as
physiology, and has advanced with
modern swiftness far beyond that of his
predecessors. It seems
strange, therefore, even to one familiar with the
movement of the
Renaissance, to be swept back nearly two thousand years
under
Harvey's guidance to reach the underlying cause of the
phenomena.
According to him the distention which stimulates the right
auricle
to contract is produced by an expansion of the blood of the
great
veins, due to the innate heat. The Harveian heart-beat is caused
and
initiated by an Aristotelian swelling up of the hot blood. Both
this
expansion and the fiery central hearth at which it is produced
have been
expelled by Harvey from within the fully developed heart;
and the primal
abode of the innate heat has been transferred to the
blood, with which that
heat has been intimately incorporated by him.
Just without the heart,
moreover, Harvey has established anew the
Aristotelian seething; making this
the result of what we to-day may
style a localized automatism of the
conjoined heat and blood. He
has localized this automatism of the hot blood
"in the vena cava,
close to the base of the heart and to the right auricle,"
_i.e._,
close to that region at and between the mouths of the two venæ
cavæ
of our present terminology, where the physiology of to-day
places,
not within the blood but in the texture of the walls which
contain
it, the seat of what is prepotent in determining the rhythm of
the
mammalian heart-beat.
Observation shows that from seemingly
pulseless peripheral veins
the blood continuously enters the venæ cavæ, which
pulsate visibly
in the region of Harvey's swelling of the blood. Yet in his
lecture
notes, in dealing with the significance of the thick resistent
walls
of the arterial vein and the aorta, he wrote: "Neither the vena
cava
nor the venous artery is of such construction, because they do
not
pulsate but, rather, are attracted."[238] On a neighboring page he
had
written:--
"At the same time [that] the pulse of the artery is
perceived by
touch, the vena cava is attracted, as it
were."[239]
We will not now search for what he meant by saying that "the
vena
cava is attracted, as it were." Clearly, however, in denying that
it
pulsates, he meant not to deny that its wall moves rhythmically, but
to
deny only that this movement is of the nature of what he styles
pulsation in
the case of the auricles or the ventricles, or the
arteries, or the arterial
vein.
We know not what influence the rhythmic movements of the wall
of
the vena cava may have had upon Harvey's transfer to its cavity of
the
Aristotelian seething of the blood. To this was referable the
palpitation
seen by him in the blood itself as the first sign of
life in the embryo and
the last sign of life in the dying animal;
and in this same familiar seething
he found ready to his hand a
life-long cause for the visible sharp expansion
of the auricle in
its diastole, for which expansion he could find no such
obvious
muscular cause as for the corresponding expansion of the
ventricle
or the arteries. The seething of the blood, however, was
carefully
kept by him below the point of vaporization and adapted to
maintain
the circulation by keeping the muscular cardiac pump at
work.
Connected with Harvey's doctrine of the cause of the
heart-beat
there is a point which a student of his thought may find
knotty,
despite the aid of a well-developed historical sense. Harvey
made
the systolic contraction of auricle or ventricle dependent on
the
mechanical stimulus of its next preceding diastolic distension.
It is
not quite easy to see how he found this process compatible
with the orderly
recurrence of all the systolic contractions in the
beating of a nearly empty
heart. It is well known that the heart may
beat for a while when cut out of
the body, when, therefore, the
heart is nearly drained of blood. In the
treatise of 1628 Harvey
himself speaks of studying the ventricular systole of
"the heart of
an eel, taken out and laid upon the table or the hand"; and
says
that the phenomena seen in this are seen likewise "in the hearts
of
little fishes, and in those colder animals in which the heart
is conical or
elongated."[240] In his lecture notes he says, we
remember, that "the
auricles pulsate after removal of the heart,
because of the multitudinous
blood."[241] But this jotting, written
only as a brief reminder for himself,
is obscure to others. By the
word "heart" Harvey means sometimes the
ventricular mass without the
auricles and sometimes the ventricular mass and
the auricles taken
together. Hence it is uncertain whether the above
reference be to
auricles left attached to the body or removed with the
ventricular
mass. In neither case is it easy to imagine effective
distention
produced by the seething even of "the multitudinous blood."
However,
in the same lecture notes a few pages farther on Harvey
says:
"Nevertheless, the heart pulsates, cut away from the
auricles;"[242]
and in the treatise of 1628 he says:--
"The heart
of the eel and of some fishes, and of animals even,
when taken out,
pulsates without auricles; indeed, if you cut
it in pieces you shall see
its divided parts contracting and
relaxing separately; so that in these
creatures the body of the
heart pulsates and palpitates after the
auricles have ceased to
move. Is this, however, peculiar to the animals
which are more
tenacious of life, whose radical moisture is more
glutinous, or
rich, and sticky,[243] and not so readily dissolved? For
in eels
the thing is apparent even in their flesh, which retains
the
power of motion after they have been skinned, drawn, and cut
in
pieces."[244]
At this point we may recall the following words
of our author:--
"I affirm also that in this way the native heat or
innate
warmth, being the common instrument of all the functions,
is
likewise the prime efficient cause of the pulse."[245]
Should
we hazard the improbable guess that Harvey meant his cause
of the heart-beat
to be effective only in warm-blooded animals, we
must remind ourselves that
it certainly was well known to him as to
all the other physicians of his day
that the heart of the mammal
beats after excision. If few had made
experiments, all had studied
Galen; and Galen cites the beating of the heart
after excision as
evidence that its beat does not depend upon the nervous
system, the
context making it obvious that he refers to the heart-beat of
the
mammal. Moreover, he makes it evident that the striking phenomenon
in
question must have been seen by the ancients at the altar, as
an incident of
sacrificial rites.[246] This fact makes it easy
to understand how it happened
that earlier still, at least two
centuries before Galen's time, the layman
Cicero, one of Harvey's
favorite authors, should have made a stoic
say:--
"It has often been observed that, when the heart of some
animal
has been torn out, it palpitates with a mobility which
imitates
the swiftness of fire."[247]
Moreover, thirty-five years
before Harvey was born, even the beating
of the excised human heart had been
seen by Vesalius, and referred
to in his celebrated treatise on anatomy, as
an incident of one of
the barbarous executions of the sixteenth
century.[248]
By no means in accord with the cause of the heart-beat
first
advocated by Harvey in 1649, is an experiment which he himself
had
brought forward in support of the circulation in 1628. In the
famous
treatise of that year he tells us that if the vena cava of a
living
snake be compressed at a point some distance away from the
heart,
the vein between that point and the heart is nearly emptied by
the
heart-beat, and the heart itself becomes paler and shrinks from
lack
of blood "and at length beats more languidly."[249] These words
show
that in this experiment the orderly heart-beats must have
continued
after the blood remaining in the vena cava had become too scanty
to
excite them by its expansion in accordance with his doctrine. It
is,
therefore, an interesting question how Harvey could reconcile
the beating of
the empty heart with his belief as to the "prime
efficient cause" of its
beat.
CHAPTER VIII
HARVEY'S DELINEATION OF THE VENOUS
RETURN
It may seem surprising that the discoverer of the venous
return
felt the need of a _deus ex machina_ to distend the right
auricle.
On reflection, however, ought it to surprise us that, although
we
find the muscular power of the heart sufficient to complete
the
Harveian circulation, Harvey himself did not, but eked it out
with
Aristotelian forces? Vigorous as Harvey was, he could not make
smooth
the road which he himself had broken. For instance, he could
not study, like
ourselves, the return of the blood to the heart
in the opened chest of an
animal anæsthetized and curarized. The
knowledge gained by his own tireless
investigations did not suffice
to teach him what we now know, viz.: that the
unaided force of the
systole of the left ventricle is sufficient to distend
the right
auricle with blood and to charge with blood the right ventricle
as
well.
The essence of Harvey's great discovery is his reversal of
the
immemorial direction of the venous flow, which he also proved to
be
abundant and rapid. But the laws which rule this flow were not,
and could not
be, patent to him as to us, owing to the imperfect
physiological knowledge of
his day. Hence at times his statements
as to the movement of the blood are
conceived in what, to borrow
an architectural phrase, may be called a
"transition style." As a
sequel to his doctrine of the cause of the
heart-beat let us pass
in review some of these statements; but, first, let us
briefly note
a few facts which may help us to realize the imperfect state of
the
science of physics in Harvey's day.
Harvey was fourteen years
younger than Galileo, who struck crippling
blows at the Aristotelian physics,
yet could not explain the common
pump;[250] and Harvey's discovery of the
circulation was made
public thirteen years before the momentous work on the
movement
of liquids done by Torricelli, who was thirty years younger
than
Harvey.[250] Moreover, it was only a year before the publication
of
the Exercises to Riolanus in Harvey's old age that Blaise
Pascal
supplied the final proof that the mercurial column below the
vacuum
of Torricelli's barometer is really sustained by the pressure of
the
atmosphere.[250] It was not till one hundred years after
the
publication of Harvey's discovery that the Reverend Stephen
Hales
published the first comparative manometric measurements of
the blood-pressure
in the arteries and the veins of the same living
animal, and stated in his
preface that "the animal fluids move by
Hydraulick and Hydrostatical
Laws."[251]
Now let us turn to some delineations of the movement of the
blood
made by Harvey himself. I have found no evidence that he knew
the
venous flow to be promoted by the aspiration of the chest; but he
knew
well the effect of the muscular movements of the body upon that
flow. Of
course he had a perfect grasp of the fundamental truth that
the main cause of
the venous return is the forcible emptying of the
ventricles into the
arteries. He says to Riolanus:--
"Among these things should be noted
the force and violence and
rapid vehemence which we perceive by touch
and sight in the
heart and greater arteries; and the systole and
diastole of
the pulse in the larger and warmer animals I do not affirm
to
be the same in all the vessels which contain blood, nor in
all
blood-containing animals; but to be such and so ample in all
that as a result thereof a streaming and an accelerated course
of the
blood through the small arteries, the porosities of
the parts, and the
branches of all the veins are necessarily
brought about; and as a result
thereof a circulation....[252]
In the case of the arteries, over and
above the shock, pulse,
or vibration of the blood (which is not equally
perceptible in
all), a continual flow and movement thence take place
until the
blood returns to the point whence it started first, namely,
the right auricle."[253] |
|
댓글 없음:
댓글 쓰기