|
Even in the days of Empedocles and Hippocrates, in the fifth
and
fourth centuries before Christ, men wrote of something derived
from
the outer air being present, for the use of the organism, in
the
vessels which also contain the blood.[46] To express this
derivative
of the outer air the ancient Greeks employed the word
"_pneuma_"
(πνεῦμα), the fundamental meaning of which seems
to have been
"air in motion." Various meanings were acquired by
"_pneuma_," such as the
breath of living things, the wind, or simply
the air, or what we mean by the
words "gas," "vapor," "steam,"
"exhalation," "emanation." The Latin word
equivalent to "_pneuma_"
is "_spiritus_," and so the English derivative of
this, the word
"spirits," came into use to express various meanings of the
Greek
"_pneuma_." A Hippocratic writer tells us that "the spirits
cannot
stand still, but go up and down" in the blood vessels. The
word
"spirits" here designates a derivative of the outer air
crudely
mingled with the blood.[47] To this writer the distinction
between
veins and arteries was unknown.
In the genuine works of
Aristotle this Hippocratic doctrine does
not reappear, though it is fairly
certain that Hippocratic treatises
which contain it were written before
Aristotle's time. We have
seen that the entrance of air into the heart, to
cool the same, is
an important feature of the Aristotelian physiology. Beyond
the
Aristotelian heart, however, we cannot trace the air which enters
it.
Yet we find "_pneuma_," "spirits," referred to by Aristotle,
not seldom
obscurely or in very general terms, as doing service,
sometimes momentous
service, in the physiology of generation and
in certain workings within the
bodies of full-grown creatures.
In disease also spirits may play a very
important part. These
Aristotelian spirits, however, when their origin can be
traced
at all, are either innate or appear to be vapor produced within
the
body itself by heat or by disease. They do not appear to be
recruited from
the outer air which has penetrated the lungs and
heart, that air seeming to
complete its function within the lungs or
within the heart itself by
sustaining the native heat which is the
great instrument of the soul, and in
which the very soul itself is
fired.[48]
Physicians of Aristotle's
time, however, revived and handed on
the doctrine that not only blood but a
derivative of the air is
distributed to the body at large through the
vessels. After the
distinction between veins and arteries had been clearly
made and
the latter had received their present name, a striking
modification
of this doctrine of the spirits was adopted and pressed by
the
Greek physician Erasistratus, about 300 B.C., not many years after
the
death of Aristotle. This modified doctrine separated the paths
taken within
the vessels by the blood and the spirits derived from
the air, and declared
the transmission of the necessary blood to
the body at large to be by the
veins only, that of the necessary
spirits, styled "vital," to be by the
arteries only. More than four
hundred and fifty years later Galen shattered
this doctrine and
incorporated the vital spirits in the arteries with the
blood, which
he proved by epoch-making experiments to be normally present in
the
arteries, he, however, clearly recognizing differences between
the
cruder blood in the veins and the spirituous blood in the
arteries.
The tissues, therefore, still received vital spirits by way of
the
arteries, according to Galen, but not spirits in their pure
gaseous
Erasistratean state.[49] Now let Galen tell us more in his
own
words:--
"The breath from the windpipes, which had been drawn
in from
without, is worked up in the flesh of the lungs in the
first
place; in the second place in the heart and arteries, and
especially in those of the net-like plexus; and to perfection in
the
ventricles of the brain, where the spirits become completely
animal. But
what the use may be of these animal spirits and
why we have the temerity
to call them so, when we confess that
we are still utterly ignorant as
to the substance of the anima
[_i.e._, of the soul], this is not the
moment to say."[50]
The complex physiology of this passage is so obsolete
that its very
phraseology is meaningless without a commentary. In the first
place,
what are the animal spirits? This expression, once a technical
term
of physiology, survives only in colloquial English, and even
there
merely as a label of which the origin is known to few. In
this
phrase the adjective "animal" does not refer to lower creatures
as
opposed to man, but is used in its obsolete original sense of
"pertaining to
the soul," for which latter the Latin word is
"_anima_," the Greek word
"_psyche_" (πσυχή). "Psychical
spirits" would best translate into the English
of to-day either
the original Greek expression "_pneuma psychikon_"
(πνεῦμα
ψυχικόν) or its Latin equivalent "_spiritus animalis_." But
the
expression "animal spirits" was for too long a time an
English
technical term to be superseded now. These animal spirits, that
is,
spirits of the soul, were not peculiar to man, but were possessed
by
lower creatures also; for neither the Latin word "_anima_" nor
the Greek word
"_psyche_" implied immortality, as the English
word "soul" is now so commonly
understood to do. Plato formally
recognized a mortal and an immortal part of
the human psyche;[51]
and Aristotle admitted the existence in animals lower
than man of
the lower grades of psyche, and conceded the lowest grade even
to
plants.[52] The perfected animal spirits were of the very
highest
physiological importance, as their name implies, they being
for
Galen no less than "the first instrument of the soul,"[53] and
thus
assuming the lofty rank given by Aristotle to the native heat.
For
Galen the animal spirits were the medium of sensation and volition
and
were imparted by the ventricles of the brain to the spinal cord
and nerves,
the fibers of which were believed, accordingly, to
consist of tubes in which
the subtile animal spirits were contained,
the bore of these tubes being too
small to be visible.
We can now follow the quoted Galenic passage and
trace the full
significance of that entrance of the substance of the air
into
the heart which Galen repeatedly acknowledged, though
sometimes
grudgingly. According to Galen whatever air was taken into the
heart
had first been "concocted" in "the flesh of the lungs." Next,
this
aerial substance had been worked up in the heart with the vapor
of
the blood into vital spirits, and these became incorporated with
the
finer blood destined for the arteries. Moreover, as each
arterial
diastole was due to an active expansion of the arterial wall,
at
each diastole there became blended with the contents of the
arteries
still more of the substance of the air, which was sucked into
the
arterial skin through the countless pores of the bodily skin,
these
being too fine to permit bleeding. The vital spirits, thus
formed and
modified, were blended with the blood of the arteries
and supplied to the
body at large. A part of these vital spirits
mounted with the blood into the
carotid arteries. In the swine and
the ruminants, notably in the calf, the
branch given to the brain by
each carotid artery breaks up at the base of the
skull within the
cranial cavity into numerous fine twigs, which form
collectively
a net-work, styled in the passage from Galen already quoted
the
"net-like plexus." This plexus is called by modern anatomists
the
_rete mirabile_. It was falsely assumed by Galen to exist in man.
The
plexuses of the two sides anastomose freely across the median
line, and
through them passes the entire blood supply of the brain;
in the animals
which possess them these plexuses seem the terminal
branches of the vertebral
arteries also. The small vessels of each
net-like plexus reunite, and thus
reconstitute the artery of the
brain before this artery has pierced the dura
mater. Galen regarded
the net-like plexus as an organ of much importance
intercalated in
the course of the artery for the still further elaboration of
the
vital spirits, which, thus altered, were exhaled from the
cerebral
arteries into the cerebral ventricles.[54] In these
ventricles
the spirits attained their final perfection, becoming
"completely
animal," by the aid of still more of the substance of the air,
which
the diastole of the pulsating brain had drawn into its
cavities
directly from the nares through the numerous holes in the
ethmoid
bones. It is a striking fact in this connection that in some of
the
domestic animals on each side of the head the cavity of the nares
is
separated from the ventricular cavity of the brain by an
exceedingly
thin, though complex, partition: as may be seen on dissection,
if
the nares and the brain _in situ_ be opened at the same time.
Now
let Galen speak again as follows:--
"I have clearly shown that the
brain is, in a way, the source of
the animal spirits, watered and fed by
inspiration and by the
abundance supplied from the net-like plexus. The
proof was not
so clear as to the vital spirits, but we may deem it not
at all
unlikely that they exist, contained in the heart and
arteries,
they, too, fed by respiration mainly, but to some degree by
the
blood also. If there be such a thing as the natural spirits,
these would be found contained in the liver and veins."[55]
The animal
spirits were sustained, as we have seen, by three kinds
of respiration which
might be called pulmonary, cutaneous and
cerebral. We may perhaps conjecture
that it was largely Galen's
acceptance of the two latter, the last
especially, which enabled him
sometimes to treat as doubtful the entrance
into the heart of that
air from which the vital spirits were held to be
derived. Of the
natural spirits he evidently made small account.[56]
A
modern physiologist, musing upon all this, might see in the vital
spirits a
dim foreshadowing of oxyhæmoglobin; might see in the
operation of the animal
spirits a plainer foreshadowing of the nerve
impulse of to-day.
Some
account, such as the foregoing, of the very complex ancient
doctrine of the
spirits is indispensable for the study of Harvey;
for that doctrine, more or
less modified, was still the accepted
medical doctrine of his time. After
this renewed study of the
ancients let us now return again to Harvey's
note-book at the place
where he takes up the question of the action of the
lungs upon the
blood otherwise than by the cooling and ventilation of the
innate
heat. It is necessary in his opinion that a further concoction
of
the blood into spirituous arterial blood should be accomplished
by the
fleshy parenchyma of the lungs in animals which require a
warmer, thinner,
"sprightly kind of aliment," as his own English
styles it.[57] The
probability of such a concoction is shown by
the separation of excreta which
indicate it, such as sputa, at the
lung.[58] On the other hand, in such
creatures as frogs and turtles
the lungs are fleshless, spongy, and
vesicular, and give no sign of
blood or excreta. Hence we may infer that the
pulmonary concoction
of the blood, though it probably occurs, is limited to
such animals
as possess fleshy and sanguinolent lungs. Hence, again, it
follows
that the concoction aforesaid is a function of secondary
importance,
because it is not universal; and that the foremost function
of
the lungs is their motion, the windpipes constituting their
most
important part, rather than the parenchyma.[59] Two functions of
the
lungs, says Harvey, are affirmed by the medical authorities:
first,
the cooling and tempering of the blood; second, the preparation
of
natural spirits and air to be made into vital spirits in the
heart.
From all this there result the excreta of pulmonary
concoction,
which are something between water and air, and the fumes which
are
breathed out in expiration continually and incessantly.
Harvey
observes correctly that Realdus Columbus had declared himself
to
have discovered the continual motion of the lung to be the
means
whereby the spirits are prepared; the blood being thinned by
the
agitation, thoroughly mixed with air, beaten, and prepared.[60]
Harvey
also cites Galen as saying that the parenchyma of the lung
concocts spirits
out of air as the flesh of the liver concocts the
blood.[61] On turning to
the Galenic passage cited by Harvey one
finds that it is out of the food that
the blood is thus concocted by
the liver.
Realdus Columbus, to whom
Harvey refers, was the Italian anatomist
who in 1559, fifty-seven years
before the Harveian circulation was
verbally announced, gave to the world the
important truth that such
blood as the right ventricle imparts to the left
reaches the latter
by traversing the pores of the texture of the lungs,[62]
instead
of the pores of the septum of the ventricles, as Galen had
taught.
The existence of these pores of the septum Vesalius had
pointedly
wondered at in 1543 and had emphatically doubted in 1555.[63]
Four
years later his former assistant and temporary successor,
Columbus,
flatly denied the existence of the pores. It was natural,
therefore,
that in the same book in which Columbus brought forward the
path
through the lungs to replace that through the septum he
should
declare that the vital spirits are made out of air worked up
with
the blood in the lungs and then merely perfected in the left
ventricle. This
doctrine was an important advance beyond what Galen
had taught, viz.: that
the spirits are but slightly prepared in the
lungs out of air and then sent
to the left ventricle to undergo
their main preparation and to be worked up
therein with the blood
which had filtered into it directly out of the right
ventricle.
So much for the views of the medical authorities. We have
found
Harvey agreeing with them that the ancient doctrine of the
cooling
and ventilation of the native heat by respiration is sound. We
have
found him acknowledging that in some animals some sort of
concoction
also of the blood destined for the arteries may be brought about
by
the pulmonary parenchyma as a function of secondary importance. But
now
we shall find him rejecting the second accepted doctrine of the
physicians,
viz.: that some of the substance of the air is taken
into the pulmonary
vessels and enters the blood. This conjecture had
had believers for two
thousand years, and was destined to be proved
true triumphantly after
Harvey's death. In rejecting it he threw
away a precious clue to the meaning
of his own great discovery.
"It is more philosophical," he says,
"not to share the common
belief that the spirits are distinct and
separate from the
humors and parts because the spirits are produced in
diverse
places or contained in diverse things," but to hold that
the
spirits and the blood are one thing, like the cream and
watery
part (serum) in milk or, to borrow a simile from
Aristotle's
reasonings about the blood,[64] like heat and water in
hot
water, or like flame and a vapor which feeds it (_nidor_).
As
light is to a candle, so are the spirits to the blood.[65]
In
this passage the discoverer's thought rises high, but in the next
it stoops
again. The next passage is headed "Spirits not from air";
and Harvey says in
effect, as I understand his difficult words:--
If spirits are made
by concoction out of air, the air is made
either thinner or thicker in
the process. If made thick, how
does it get from the windpipes into the
venous artery? If the
spirits be thinner than air, how are they held[66]
by the
tunic of the lung, since this lets pass the pus and serum
of
empyema?[65]
In the treatise of 1628 Harvey says that
Laurentius
"asserts and proves that, in empyema, serosities and
pus
absorbed from the cavity of the chest into the venous artery
may
be expelled and got rid of with the urine and fæces through
the
left ventricle of the heart and the arteries."[67]
Harvey's
argument in his note-book continues thus:--
"How, since mixture
consists in the union of altered matters,
can air be thoroughly mixed
and made one with blood? What is
that which mixes and alters? If it be
heat, the air is made
thinner thereby. If it be urged that the air is
thickened by
cold during preparation (which is impossible in the lungs),
then
Aristotle's[68] argument holds good: if spirits be from the
air,
how about fishes, which are agile and abound in
spirits?"[69]
At this point we may call to mind passages in the
introduction to
Harvey's treatise of 1628, published more than eleven years
after
he had written the notes which we are now studying. In one of
these
passages he speaks of what is now called the pulmonary
vein,
saying:--
"If it be contended that fumes and air pass to
and fro by this
road, as through the bronchia of the lungs, why can we
find
neither air nor fumes on dissection, when the venous artery
has
been cut out or cut into? And how comes it that we always
see
the aforesaid venous artery to be full of thick blood and
never
of air, while we perceive that there is air remaining in
the
lungs?"[70]
Immediately after the foregoing passage Harvey
says that should an
experimenter
"make a cut in the trachea of a
living dog, forcibly fill the
lungs with air by means of a bellows and,
when they have been
distended, apply a firm ligature, on opening the
chest shortly
after, he would find great abundance of air in the lungs,
up to
their outermost tunic, but none at all in the venous artery
or
in the left ventricle of the heart. If in the living dog the
heart drew air out of the lungs or the lungs transmitted it,
much more
ought they to do so in this experiment. Who, indeed,
could doubt that
even in a dissection, if the lungs of a dead
body had been inflated, air
would enter at once, as aforesaid,
did any passages
exist?"[71]
Yet we have found Aristotle, more than nineteen centuries
before
Harvey, recognizing that no passages are needed for the transfer
of
air out of the windpipe, and saying, of the channels from the
heart,
that "it is by contact that they receive the breath[72] and
transmit
it to the heart."[73] Moreover, sixty-nine years before
Harvey's
publication Columbus had repeatedly recommended the experiment
of
opening the venous artery[20] in a living dog and noting that the
"said
venous artery" is full of blood, not of air or fumes. But
Columbus held this
observation rather to confirm than to disprove
his doctrine that the blood in
the venous artery is imbued with
vital spirits derived in the lungs from the
substance of the air.
Indeed, he goes so far as to call the contents of this
vessel
"modified blood and air."[74] In this matter the earlier
observer,
Columbus, shows keener insight than the later,
Harvey.
Decidedly, however, the stage waits for the chemists,
despite
Harvey's poor opinion of them. Despite that poor opinion,
too,
Harvey himself turns to making chemical conjectures in the
next
passage of his note-book, to the study of which latter we will
now
return. The passage is as follows:--
"Conclusion. Opinion of
W. H.
"In animals in which lungs are fleshy and full of blood
these
concoct the blood, seeing that spirits and blood are one
thing, in the same way that the liver does and by reason of
the same
arguments; indeed, the lungs may rather detain fatty
and oleaginous
vapor by a cooling process, as oil or balsam or
nutritious fat is cooled
in alembic and serpentina"[75]--
"alembic" and "serpentina" answering to
the "still" and "worm"
of the modern distiller. Harvey, therefore, utilizes
the Galenic
analogy between concoction in the lungs and that of the
blood
and the vapors thereof, rejecting not only Galen's
preliminary
concoction of air into spirits in the lungs, but also
Columbus's
union in the lungs of blood with spirits produced in the
lungs
themselves out of air. Of the entrance of "the substance of
air"
into the blood Harvey makes emphatic denial and, by so doing,
reduces
the spirits either to emanations from ingredients of the
body itself (thus
reminding us of Aristotle), or to a mere name with
which to label qualities
of the blood, in treating of which he often
uses the word "spirits" as a
current term. Naturally, therefore,
where in his lecture notes he treats of
the spirits in relation
to the brain and nerves his conclusions are not
clearly defined,
but seem consistent with his views as to the spirits in the
blood,
though his jotted words are not very easy to understand. On
this
subject he refers by name to Galen, three alternatives discussed
by
whom appear to be reviewed by Harvey, viz.: that sensation and
motion result
either from a progression from elsewhere of spirits
in substance along and
within the nerves; or from a vibration of
spirits in substance which have
their native seat within the nerves;
or, lastly, from no movement of a
substance, but from a transfer
of "faculty" along the nerves by means of
progressive qualitative
alteration thereof, "such as is produced in air by
the brightness
of the sun."[76] Of these three alternatives, the last seems
to
commend itself most to Harvey, as we should expect; the second,
next;
and the first, not at all;--that is, if one may so interpret
the following
brief passage of his lecture notes:--
"I believe that in the nerves
there is no progression of
spirits, but irradiation; and that the
actions from which
sensation and motion result are brought about as
light is in
air, perhaps as the flux and reflux of the
sea."[77]
Also we find Harvey long years afterward saying to
Riolanus:--
"Moreover, the spirits, animal, natural, vital, which
dwell,
contained within blind windings, in solid parts, to wit,
in ligaments and nerves (especially if there be so many
kinds),--these
spirits are not to be regarded as so many diverse
aereal forms, nor as
so many kinds of vapors."[78]
In Harvey's lecture notes the subject of
respiration is brought to
an end with an abrupt interrogation, which seems to
reveal a sudden
return of doubt as to whether too much may not have been
conceded in
admitting a pulmonary concoction of any sort. We
read:--
"N.B. If the blood receive concoction in the lungs, why does
it
not traverse the lungs in the embryo?"[79]
It would seem to be
Harvey's tendency to adhere to the view
which limited the use of respiration
entirely to the cooling and
ventilation of the innate heat, by which
according to ancient
doctrine the heart was the central hearth, embedded in
the cooling
and ventilating lungs; although this ancient doctrine tallied
well
in most eyes with the belief that only a portion of the blood
ever
entered the heart at all.[80] In the first of the two Exercises
which
Harvey, when seventy years old, in 1649, addressed to Riolanus
in defense of
the circulation, the ancient respiratory cooling and
ventilation take their
place again as follows:--
"Thus by the aid of two extremes, viz.:
cold and heat, is the
temperature of the animal body retained at its
mean. For as
the air inspired tempers the too great heat of the blood
in
the lungs and centre of the body and effects the expulsion of
suffocating fumes, so in its turn does the hot blood, thrown
through the
arteries into the entire body, cherish and nourish
and keep alive all
the extremities, preventing extinction due to
the power of external
cold."[81]
In none of the writings of his old age does Harvey deal
expressly
with concoction in the lungs, or more than cursorily with
the
entrance of the substance of air into the blood. But he repeatedly
and
emphatically reaffirms that blood and spirits are one thing;[82]
he even
declares the blood in comparison with the other parts of
the body to be
"possessed of powers of action beyond all the rest,
and therefore, in virtue
of its preeminence, meriting the title
of spirit."[83] He castigates those
who give the rein to overmuch
speculation about the spirits. We learn that
some suppose that the
spirits "are engendered and are fed and increased from
the thinner
part of the blood"; that others suppose "the primigenial
moisture"
to engender and support them.[84] Then there are "those who tell
us
that the spirits are formed in the heart, being compounded of
the
vapours or exhalations of the blood (excited either by the heat of
the
heart or the agitation) and the inspired air"[85]--the
Galenic
doctrine.
"Such spirits," says Harvey of these last
mentioned, "are rather
to be regarded as fumes and excrementitious
effluvia of the
blood and body, like odours, than as natural artificers;
...
whence it seems probable also that pulmonary expiration is
for
the ventilation and purifying of the blood by the breathing
out of these; while inspiration is in order that the blood, in
passing
through between the two ventricles of the heart, may
be tempered by the
ambient cold; lest the blood, being hot and
swollen, blown up in a sort
of ferment, like milk and honey
boiling up, should so distend the lungs
that the animal would be
suffocated."[86]
As we read these words,
published in Harvey's old age, we recollect
the following words, written in
his note-book more than thirty-three
years before, viz.: "So there is cooling
and ventilation of the
native heat, ventilation especially."[87]
We
may recall also that the preservation of the native heat had
sufficed to
explain respiration to Harvey's ancient teacher,
Aristotle, while the tenor
of Aristotle's genuine works well accords
with the following dictum which we
have found in Harvey's note-book:
"Spirits not from air." Yet the more firmly
this dictum was upheld,
and the more simply Aristotelian in principle did
Harvey's doctrine
of respiration remain, so much the less called for must
have
seemed that swift and endlessly repeated passage through the lungs
of
the whole mass of the blood, which was involved in the
Harveian
circulation.
In the actual phenomena of respiration, however,
positive obstacles
confronted the doctrine of the circulation which were
harder to
surmount than cobwebs of speculation, or than the mere
question
"_cui bono_" which latter the steadfast observer could
simply
wave aside. Spirits or no spirits, there were opponents of
the
circulation, even in Harvey's old age, who insisted that the blood
in
the arteries was so different from the blood in the veins that
the same blood
could not be changing perpetually from arterial to
venous, and _vice versa_.
There was always that stubborn difference
of color, plainly to be seen in man
and beast, but so hard to
account for in Harvey's day. Therefore, we find
Harvey leaving the
realm of subtleties and taking up his old weapon of
demonstration,
in order to minimize the differences between arterial and
venous
blood. Twenty years after the publication of his discovery he
says
to Riolanus:--
"You may also perform another experiment at
the same time.
If you fill two cups of the same measurement with blood,
one
with that which issues by leaps from an artery, the other
with
venous blood from a vein of the same animal, you can
observe
the sensible differences between the two, both immediately
and
later, when the blood in either cup has become coagulated
and
cold. This experiment will contradict those who pretend that
the blood in the arteries is of one kind, that in the veins of
another,
on the ground that that in the arteries is more florid
and seethes and
is blown up with copious spirits, I know not
how, like milk or honey
boiling upon the fire, swelling and
filling a larger space. For, were
the blood which is thrown
from the left ventricle of the heart into the
arteries fermented
thus into a frothy and flatulent condition, so that a
drop or
two distended the whole cavity of the aorta,
unquestionably,
upon the subsidence of this fermentation, the volume of
the
blood would return to that of a few drops (and this is,
indeed,
the reason that some assign for the empty state of the
arteries
in the dead body); and this would be apparent in the cup
which
is full of arterial blood, for so we find it to happen in
milk
and honey when they come to cool. But if in both cups you
find blood nearly of the same colour, not of very different
consistency
in the coagulated state, forcing out serum in
the same manner and
filling each cup to the same height when
cold that it did when hot, this
will be enough for any one
to rest his faith upon, and afford argument
enough, I think,
for rejecting the dreams of certain people. On
investigation
sense and reason alike assure us that the blood of the
left
ventricle is not of a different kind from that of the
right....
The blood, then, when imbued with spirits to the utmost, is
not
swollen with them, or fermented or blown up so as to crave
and
require more ample room (as can be determined with the
greatest
certainty on trial by the measurement of the cups); we
should
rather understand this blood to be possessed, after the
manner
of wine, of greater strength, and of an impetus to action
and
effectiveness, in accordance with the view of
Hippocrates.
"So the blood in the arteries is the same as that in
the veins;
even though the former be acknowledged more spirituous
and
possessed of greater vital force; but the blood in the
arteries
is not converted into something more aereal or rendered
more
vaporous; as though there were no spirits not aereal, nor
anything which gives an impetus except wind and flatulence."[88]
It is
well, one may be inclined to mutter, as one reads this, but
how about the
color? It may be nearly the same, but certainly
there is a difference. In his
book "On Generation" Harvey himself
describes in more detail the changes
which occur in shed blood on
standing, and says: "Of the red parts the upper
are more florid,
those below are blackish." In the same description he
refers
shortly after to "the florid and ruddy part which is
commonly
thought to be arterial blood."[89] The words last quoted
evidently
refer to the upper part of coagulating blood as commonly seen.
This
in medical practice would be blood drawn from a vein, and Harvey
says
nothing of arteriotomy in this passage. Indeed, he refers
in the context to
venesection; and earlier in the same chapter
he wrote: "Physicians observe
only human blood, and this shed by
venesection into a basin, and
coagulated."[90]
The foregoing passages show at once that opinions had
been clarified
very little by the suggestive change of color caused in shed
blood
by contact with air. Years before, in jotting down his
lecture
notes, Harvey had noted that the arterial blood is redder;[91]
Galen
had known it;[92] it must always have been known. In 1649
Harvey
wrote:--
"Three things are especially apt to give rise to
this opinion of
the diversity of the blood: the first is that the blood
which
is drawn in arteriotomy is more florid....[93] Whenever
and
wherever blood issues through a narrow orifice it is
strained,
as it were, and the thinner and lighter part, which
usually
swims on top and is the more penetrating, is
emitted."[94]
A number of observations follow, of appearances noted in
nosebleed,
in the use of leeches, in cupping, and in blood-letting from
veins
and arteries. All these appearances are adduced in support of
the
view that it is the straining of the blood which renders it
more
florid, and they all show that the brightening of the color of
shed
blood on exposure to air served only to lead Harvey off on a
false
scent. Continuing he refers, as follows, to direct inspection of
the
dissected lungs:--
"The blood is found to be much more florid
within the lungs and
after it is squeezed out of them, than in the
arteries."[95]
A few pages farther on he states, categorically, the
false
conclusion to which he has been driven, saying:--
"It is no
less plain why the blood of the lungs is so ruddy; for
it is thinner,
because there it is filtered through."[96]
Nothing indicates better
Harvey's readiness to minimize the
essential differences between venous and
arterial blood than a
passage in the treatise of 1628, in which he says that,
compared
with the left ventricle, the right ventricle "is of
greater
capacity, that it may supply not only matter to the left
ventricle,
but also nourishment to the lungs."[97] It should be
remembered
that, in Harvey's day, the so-called bronchial arteries were
still
unknown, through which the tissues of the lungs are supplied
with
arterial blood from the aorta.[98] Not only Columbus,[99] but
even
Galen,[100] had each devised an erroneous way in which to provide
the
lungs with "spirituous" or "vital" blood, in addition to the
venous blood
from the right ventricle; but Harvey is obviously
content to let the latter
suffice for their nutrition.
What has gone before indicates how erroneous
it is to speak of the
pulmonary transit, as Columbus had set it forth in
1559, nineteen
years before Harvey's birth, as though Columbus were in some
sort
a sharer in the discovery of the circulation. Those who so speak
fail
to note the difference between blood and _the_ blood. Although
Columbus
girded at Galen and corrected him, Columbus's pulmonary
transit of a fraction
of the blood by curing more than one defect of
the Galenic doctrine
strengthened the erroneous Galenic physiology
of the blood-movement. Of these
larger features Columbus not
only was no enemy, but remained a devoted
adherent. His doctrine
certainly paved the way for Harvey's, but in no more
immediate sense
than did Galen's doctrine that blood is naturally contained
in the
arteries.[80]
Indeed, Harvey categorically stated that the
movement of blood
through the lungs had nothing to do with his discovery. In
a Latin
letter from London written in 1651 to P. M. Siegel in
Hamburg,
Harvey says in his old age:--
"Meantime, as Riolanus
uses his utmost efforts to oppose the
passage of blood into the left
ventricle through the lungs, and
brings it all hither through the
septum, and so vaunts himself
as having upset the very foundation of the
Harveian circulation,
(although I have nowhere laid that down as a
foundation for
my circulation; for the blood fetches a circuit in very
many
red-blooded animals in which no lungs are to be found), it
may
be well here to relate an experiment which I lately tried in
the
presence of several of my colleagues, and from the cogency
of
which there is no escape."[101]
The parenthesis certainly is a
striking one.
No less striking is the last word published by Harvey
about
respiration. We have heard him deny the entrance of air into
the
blood and doubt the occurrence of any concoction in the lungs. Now
we
shall hear him throw over even the cooling of the innate heat, a
respiratory
doctrine to which he has seemed hitherto to hold with
conviction. In the
essay "On Parturition" published in 1651 with the
treatise "On Generation,"
he says:--
"In the meantime I would propose this question to the
learned:
How comes it that the fœtus continues in its mother's
womb
after the seventh month? If brought forth at that time it
breathes at will, indeed could not survive one little hour
without
breathing; yet, as I have said, if it remain in the womb
it keeps alive
and well beyond the ninth month without the aid
of respiration.... Whoso
shall attend carefully to these things
and consider more closely the
nature of air, will, I think,
readily grant that air is given to animals
neither for cooling
nor as nutriment; for it is a fact that after the
fœtus has
once drawn breath it may be suffocated more quickly than
when
entirely excluded from the air; as though heat were unkindled
by
air within the fœtus rather than allayed. Thus much, merely
by the way, on the subject of respiration; perhaps I shall treat
of it
more fully in its proper place. Surely a more knotty
subject could
hardly be found, as the arguments on both sides
are very evenly
balanced."[102]
So we find Harvey in his old age induced by lifelong
study to
question, if not deny, even the cooling effects of
respiration,
and to end with a practical confession of ignorance.
Instead,
therefore, of the circulation and its swiftness being explained
by
the urgent need of "the substance of the air" experienced by
certain
tissues, that movement of the whole mass of the blood through
the
lungs, which was so novel a physiological fact, does not seem to
have
affected his view of the problems of respiration. Nor could he
properly
explain the respiratory change in the color of the blood,
which seemed to
support the ancient doctrine that the blood is
of two different kinds. Since
he could not invoke respiration to
elucidate the circulation and its
rapidity, and since he himself
declared that such rapidity could not be
needed for the simple
feeding of the tissues, what was left to be invoked? It
is no wonder
that eight years[103] after the publication of his discovery
Harvey
denied that he had ever seriously undertaken to explain the use
of
the circulation; that at the end of thirteen years more he
repeated
this denial in his old age;[104] although he had not refrained
from
expressing such conjectures as must always be evoked in the mind
of a
great observer by a discovery of the first importance made by
himself. Yet
the phenomena of the very circulation used were so
striking as to cry aloud
for elucidation; for Harvey's own clinching
statement that the heart drives
into the aorta at least one thousand
drachms of blood in half an hour,[105]
this _reductio ad absurdum_,
which cut the ground from under the feet of his
opponents, left him
helpless in his turn to account for the need of so huge a
flooding
of the arteries.
Since it was not to be swiftly altered in
the lungs that the whole
mass of the blood hurried back from all parts of the
chest, what
then?
CHAPTER IV
THE CIRCULATION AND
THE ARISTOTELIAN PRIMACY OF THE HEART
It has been stated already that
the first announcement of the
circulation is to be found in Harvey's lecture
notes. The following
is the text of the memorable passage in question, which
I have
translated from Harvey's Latin. He says:--
"It is proved
by the structure of the heart that the blood is
perpetually transferred
through the lungs into the aorta, as
by two clacks of a water-bellows to
rayse water. It is proved
by the ligature that there is a transit of the
blood from
the arteries to the veins; whereby it is demonstrated that
a
perpetual movement of the blood in a circle is brought about
by
the beat of the heart. Is this for the sake of nutrition, or
of
the better preservation of the blood and members by infusion
of
heat, the blood in turn being cooled by heating the members
and
heated by the heart?"[106]
The words "as by two clacks of a
water-bellows to rayse water"
are Harvey's own racy English, embedded in his
Latin text. The
"ligature" is the flat band which is tied about the upper arm
when
bleeding from a vein is to be practised at the bend of the elbow.
The
Hippocratic physicians called this band a "_taenia_,"[107] and
even in their
day it was known to hasten the flow of blood from
the opened vein when
applied as above stated, but yet to check the
flow if tied too tight. This
clinical observation had awaited
a rational explanation for more than
nineteen centuries.[108]
[Illustration:
Page 80, right, of William
Harvey's _Prelectiones Anatomiæ
Universalis_, or Lecture Notes of 1616. The
passage contains the
first recorded mention of the movement of the blood in a
circle.]
[Illustration:
WH constat per fabricam cordis
sanguinem
per pulmones in Aortam perpetuo
transferri, as by
two clacks of a
water bellows to rayse water
constat per
ligaturam transitum sanguinis
ab arterijs ad venas
vnde Δ
perpetuum sanguinis motum
in circulo fieri pulsu cordis
An?
hoc gratia Nutritionis
an magis Conservationis sanguinis
et
Membrorum per Infusionem calidam
vicissimque sanguis
Calefaciens
membra frigifactum a
Corde
Calefit
Transcript of the preceding page.]
Our
most immediate interest in the foregoing passage lies in this:
that on the
very same page, with the few clear simple words which
tell for the first time
of Harvey's facts and proofs, he has briefly
written down conjectures as to
the meaning of the circulation.
These are as strikingly put as certain
jottings are obscure which
deal on a neighboring page with some possible
meanings of the
heart-beat.[109] In neither group of conjectures do the
functions of
the lungs play a part; but the discoverer asks himself whether
it
be not to revisit the heat of the heart that the whole mass of
the
blood circles back to the chest in its Harveian course! More
than
thirty-two years after the date of Harvey's note-book Harvey wrote
to
Riolanus:--
"There are some who consider that as no impulsion of
nutriment
is required for the nutrition of plants, their
particles
attracting little by little whatever they need to replace
what
they have lost, so in animals there is no need of any
impulsion,
the vegetative faculty in both working alike. But there is
a
difference. In animals a perpetual flow of warmth is required
to
cherish the members, to keep them alive by the aid of
vivifying
heat, and to restore parts injured from without. It is
not
merely nutrition that needs to be provided for."[110]
In the
first Exercise to Riolanus Harvey had touched also upon the
use of the
circulation, interweaving this doctrine of heat with the
doctrine of
respiration as he then held it, in a passage the last
part of which I have
quoted already. Quoted more fully he says:--
"And this, indeed, is
the principal use and end of the
circulation, for which the blood
revolves with perpetual
influence in its ceaseless course and is driven
along its
circuit: namely, that all the parts in dependence upon
the
blood may be kept alive by the primary innate heat and in
their
state of vital and vegetative being, and may perform all
their
functions; whilst, to use the language of physiologists,
they
are sustained and actuated by the inflowing heat and vital
spirits. Thus by the aid of two extremes, viz.: cold and heat,
is the
temperature of the animal body retained at its mean. For
as the air
inspired tempers the too great heat of the blood in
the lungs and center
of the body and effects the expulsion of
suffocating fumes, so in its
turn does the hot blood, thrown
through the arteries into the entire
body, cherish and nourish
and keep alive all the extremities, preventing
extinction due to
the power of external cold."[111]
"The innate
fire is not in the right ventricle," a Hippocratic
author had written, who
had written also that the wall of the
left ventricle is dense, to guard the
strength of the heat.[112]
Aristotle, too, had placed in the heart the
"origin" of the "natural
innate heat";[113] had likened the heart to "the
hearth on which
shall lie the natural kindling, well protected also, as being
the
acropolis of the body."[114] At a later day Galen had affirmed
the
same doctrine.[115]
Let us turn now to the famous treatise of
1628, published twelve
years after the note-book had been written. In the
chapter in which
Harvey says "I tremble lest I have mankind at large for my
enemies"
and then publishes and names the circulation,--in this
chapter,
before passing to his proofs, he published the following
words
which resound in a way very different from the simplicity of
the
note-book:--
"So probably it may come to pass in the body
through the
movement of the blood that all the parts are
nourished,
cherished, quickened, by the hotter, perfected,
vaporous,
spirituous, and, so to speak, alimentive blood; that the
blood,
on the other hand, is cooled, coagulated, and rendered, as
it
were, effete in the parts; whence it returns to its origin,
namely, the heart, as to its fountain, or the hearth of the
body, to
regain perfection. There by the potent and fervid
natural heat, a
treasury of life, as it were, the blood is
liquefied anew and becomes
pregnant with spirits and, so to
speak, with balsam. Thence the blood is
distributed again; and
all this depends upon the motion and pulsation of
the heart.
"The heart, therefore, is the origin of life and the sun
of the
microcosm, even as the sun in his turn might well be called
the
heart of the world; by the vigor and pulsation of the heart
the blood is moved, perfected, quickened, and delivered from
corruption
and thickening; and the function of nourishing,
cherishing, quickening
the entire body is performed by that
intimate hearth, the heart, the
foundation of life, the author
of all. But of these matters more
conveniently when I shall
speculate as to the final cause of motion such
as this."[116]
Upon this florid passage follow the classic six chapters
which bring
forward with such power and calm the proofs of the
circulation.
These are succeeded in their turn by words which echo their
sobriety, as follows:-- |
|
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