RESPIRATION AND THE CIRCULATION
So the feeding of the tissues could not sufficiently account, to
Harvey's mind, for the swiftness of the circulation. What could?
It is easy for us to recite the multitudinous modern duties of the
blood as a bearer of cells and of chemicals from point to point and
as a protector against poisoning; above all it is easy to exclaim
"respiration";--to read the most striking part of the riddle by
knowing the answer which was wrung laboriously from Nature after
Harvey had died. It is easy for us to see that speedy death from
loss of the circulating blood is practically the same as death
from ligature of the arteries of the brain, or from drowning,
or strangulation, or a broken neck. But this was veiled from
him, and what best accounts for the volume and swiftness of the
Harveian circulation was, in Harvey's day, a stumbling block to its
acceptance; for no adequate reason was apparent why the whole mass
of the blood should traverse the lungs, or why, if the veins receive
their blood from the arteries, the venous blood should differ in
color from the arterial.
Let us remember that throughout Harvey's life air was still an
elementary body in the eyes of many and, for all, blood was a quite
mysterious, ruddy, hot, vital liquid. Only weak magnifying glasses
were available for him, and the powerful lenses of Malpighi and van
Leeuwenhoek had not yet revealed to the world either capillary or
blood-corpuscle. Moreover, the gossiping John Aubrey, the man who
had been advised about his youthful studies by Harvey, wrote of him
some years after his death, that "he did not care for Chymistrey,
and was wont to speake against them [the chemists] with an
undervalue."[19] Where would physiology be to-day, had not histology
and chemistry long stood in the forefront beside her?
In a passage of the treatise of 1628 Harvey speaks of respiration,
as follows:--
"And now it has come to this, that it would seem better worth
while and more straightforward for those who seek the path by
which in man the blood passes through the vena cava into the
left ventricle and the venous artery,[20] to be willing to
search for the truth by dissecting animals, in order to look
for the reason why in the larger and more perfect animals, when
full grown, nature chooses to make the blood percolate through
the parenchyma of the lungs rather than take wide open paths as
in all other animals (it being understood that no other path
and transit can be thought out):--whether it is because the
larger and more perfect animals are hotter and when they are
full grown their heat is more ignited, so to speak, and prone
to be smothered, that there is this permeation and transfer
through the lungs in order that the heat may be tempered by the
inspired air and guarded from boiling up and smothering--or for
some other similar reason. But to determine these matters and
explain them completely were to enter on a speculation as to the
purpose for which the lungs are made. About these and their use
and motion, and the whole subject of ventilation and the need
and use of air, and other matters of this sort, and about the
various different organs created in animals by reason thereof,
although I have made a vast number of observations, I shall not
speak till I can more conveniently set them forth in a treatise
apart, lest by wandering at this point too far from my subject,
which is the motion and use of the heart, I should seem to deal
with something else and leave my position, to confuse and evade
the question."[21]
Farther on in the same treatise Harvey says:--
"Moreover, the reason why the lungs have vessels so ample, both
vein and artery, that the trunk of the venous artery exceeds
in size the crural and jugular branches taken both together;
and the reason why the lungs are so full of blood as we know
them to be by experience and inspection (heeding Aristotle's
warning,[22] and not deceived by the inspection of such lungs as
we have removed from dissected animals from which all the blood
had flowed out)--the reason is, that in the lungs and heart
is the storehouse, the source, the treasury of the blood, the
workshop of its perfection."[23]
So the great Englishman gropes for a moment or two by the light of
ancient Greek doctrines and puts the question of respiration by. But
this very attitude shows Harvey's thought to be in such contrast
with the thought of to-day that in order to understand him we need
to learn more fully his views of respiration; and we find with
satisfaction that in his lecture notes of more than eleven years
before he had not put this question by, for he had been called upon
to lecture upon the uses of the lungs. We must seek in his lecture
notes, therefore, for what he had thought those uses to be. These
notes, however, we shall be unable to follow unless now, first of
all, we shall give the floor for a while to the ancients; for from
their doctrines Harvey necessarily took his cue, like the other
thinkers of his time.
The momentous physiological facts that the living body of man,
beast, or bird, is warm of itself and that its cooling means its
death, must always have struck and impressed the human mind, whether
trained or untrained. More than nineteen centuries before Harvey
certain thoughts of Aristotle were recorded as follows:--
"In animals all the parts and the entire body possess a certain
innate natural heat; wherefore they are sensibly warm when
living, the reverse when making an end and parting with life.
In the animals which have blood the origin of this heat is
necessarily in the heart, in the bloodless kinds in the analogue
thereof; for all work up and concoct the nourishment by means of
the natural heat, the master part most of all. Life persists,
therefore, when the other parts are chilled; but if what
resides in this one be so affected total destruction ensues,
because upon this part they all depend as the source of their
heat, the soul being as it were afire within this part; that
is, within the heart in the animals which have blood, in the
bloodless kinds in the analogue thereof. Necessarily, therefore,
the existence of life is coupled with the preservation of the
heat aforesaid, and what is called death is the destruction
thereof."[24]
This heat which is innate in all living animals was styled by
Aristotle not only "innate" but "natural," "vital,"[25] and
"physical,"[26] it being indispensable to life and to the working
of the soul. He held the continued existence of the innate heat to
depend upon conditions similar to those under which a fire is kept
alive, viz.: protection both from burning out and from extinction
due to external forces. Yet the true nature of combustion was not
settled till more than a century after Harvey's death. The fact
that air is necessary to fire must always have been a matter of
common knowledge. Therefore, the views of the relations of air to
fire maintained by Aristotle nearly twenty-one centuries before the
discovery of oxygen did not seem naïve to Harvey, whatever they
may seem to us. Aristotle held that air exerts upon fire a cooling
influence which saves it from burning out too fast; and that the
same influence is exerted upon the vital innate heat of animals
by the air which they breathe in, or the water which bathes their
gills.[27] Moreover, Aristotle says:--
"Why those animals breathe most which have lungs containing
blood, is plain from this: that the warmer an animal is, the
greater need it has of cooling, while at the same time the
breath passes easily toward the source of warmth within the
heart. But the way in which the heart is pierced through toward
the lung must be studied from dissections and from the history
of animals which I have written. In general terms, then, it is
the nature of animals to need cooling on account of the firing
of the soul within the heart."[28]
In the treatise styled the "History of Animals," to which he refers
us, Aristotle says:--
"There are also channels from the heart which lead into the lung
and divide in the same way as the windpipe, and they accompany
the channels from the windpipe throughout the entire lung. The
channels from the heart lie uppermost; but no common channel
exists, for it is by contact[29] that they receive the breath
and transmit it to the heart."[30]
The collection of ancient Greek commonly called the "Works of
Hippocrates" is judged to be of the fifth and fourth centuries B.C.
There is included in this collection a brief treatise on the heart;
and in this occurs the earliest known account of the structure and
use of the semilunar valves, which together with the rest of the
cardiac valves were unknown to Aristotle. In the same Hippocratic
treatise the doctrine is adhered to of the entrance of air into the
heart for cooling purposes, both the right and the left ventricle
being specified as receiving it. The author says:--
"The vessel which leads out of the right ventricle ... closes
toward the heart, but closes imperfectly, in order that air may
enter, though not very much."[31]
This piece of incorrect physiology may well have received support
from the fact that the pulmonary semilunar valve is commonly found
to be not quite competent when the dead and dissected pulmonary
artery of the bullock is distended with water--an observation which
the ancient author intimates that he has made,[32] though he does
not specify the creature dissected.
Nearly five hundred years after the death of Aristotle, the analogy
between life and flame was discussed, formally and at some length,
by Galen. He knew his Aristotle well, and agreed with him as to the
importance of respiratory cooling for protracting the indispensable
heat of animals.[33] But we find Galen dealing with the uses of
respiration in a less simple way than Aristotle. In a polemical
treatise Galen debates the question whether "the breath drawn in
in respiration" actually enters the heart, or whether it cools it
without entering it. He says:--
"It is possible that the whole is breathed out again, as was
believed by most physicians and philosophers, and those the
keenest, who say that the heart, while it craves to be cooled,
is in need not of the substance, but of the quality[34] of the
breath, and that the use of respiration is indicated by the
part.... I have shown in my treatise on the use of respiration
that either an absolutely minute quantity, or none at all, of
the substance of the air, is taken into the heart."[35]
It is clear, however, that Galen, when delivering himself of the
foregoing, was a trifle carried away by the ardor of contention; for
in the very treatise to which he refers us, as well as elsewhere,
he not only dilates upon the cooling effects of breathing,
but admits the entrance of air into the heart for a definite
physiological purpose. This purpose, however, which we shall study
later, is not cooling and is counted of secondary importance by
Galen. Nevertheless, he goes so far as to say this:--
"That some portion of the air is drawn into the heart in its
diastole and fills the vacuum which is produced, is sufficiently
shown by the very magnitude of the dilation."[36]
In his treatise "On the Use of the Parts of the Human Body" Galen
takes a more judicial tone in the following brief, calm summary:--
"The use of the respiration of animals arises from the heart,
as has been shown. The heart itself needs in some sort the
substance of the air; but, first and foremost, it craves to
be cooled, because it boils with heat. The heart is cooled by
the cool quality of inspiration; but expiration also cools, by
pouring out that which seethes within the heart and is, in a
way, burned up and sooty."[37]
Thus do we see the modern products of respiration foreshadowed.
Galen believed that the heat of animals is safeguarded also by the
entrance of cooling air through the pores of the skin into the
arterial system, and by the exit through these pores of injurious
fumes out of the arteries.[38] In the introduction to Harvey's great
treatise of 1628[39] the English physician riddles with adverse
arguments this doctrine of Galen; to this we shall return later, as
we shall to Galen's belief that the brain draws cooling air directly
into its ventricles out of the nares through the cribriform plate of
the ethmoid bone.[40]
In passing from Aristotle to Galen we have crossed nearly five
centuries. Now let us pass at a leap across fourteen centuries
more, from Galen at imperial Rome under Septimius Severus to Harvey
at London under King James the First. Having briefly scanned the
doctrines of the Greeks, let us take up our study of respiration
in Harvey's private lecture notes of 1616. His crabbed handwriting
has been deciphered by experts, and his notes have been both
photographed and printed. If we seek therein for his thoughts about
respiration, and track them through the jungle of abbreviated
careless Latin and racy English in which they were jotted down, we
shall find them Galenic in part, but also denying a truth which
Galen had accepted. Harvey's notes are often too disconnected for
quotation, calling rather for paraphrase or summary; and to make
either is a task which one cannot approach without diffidence,
especially as this task involves translation also. Of what I have
ventured to prepare to represent parts of Harvey's note-book in the
present paper some passages are simple translations, such English
words as Harvey interspersed being transcribed. Naturally such
passages are included between quotation marks. These are not used,
however, in the case of a paraphrase or summary, even if it contains
scattered English words which are Harvey's own.
Harvey fully shared the ancient view of the supreme importance
of the heat of animals. In his note-book he, like Galen, deals
with respiration under the heads: first, of a possible absorption
of some of the substance of the air; and, second, of cooling and
ventilation. Let us first take up the second head. Harvey says:--
"Without nourishment life cannot be, nor nourishment without
concoction, nor concoction without heat, nor heat without
ventilation;" for heat perishes either of wasting or of
smothering; "so there is cooling and ventilation of the native
heat, ventilation especially."[41]
His words contain reminders of Aristotle;[24] and he continues about
respiration in a vein as ancient as Hippocrates,[42] as follows:--
"Nothing is so necessary, neither sense nor food. Life and
respiration are convertible terms, for there is no life without
breathing and no breathing without life. If the eye be cut out
there is an end of seeing; if the legs be cut off there is
an end of walking; if the tongue, of speech, _et cetera_; if
respiration, there is an end of everything immediately."[43]
When Harvey jotted this down he had in mind a Galenic passage which
doubtless had become the common property of all physicians in his
day; for the removal of eye and legs figures in the first chapter of
Galen "On the Use of Respiration."[44] Harvey continues:--
"Hence large animals are much warmer and breathe frequently,
because they have need of greater cooling and ventilation
inasmuch as they very greatly abound in blood and heat."[45]
In the margin opposite this passage there is written:--
"Why and how air is needed by animals which breathe and also air
is necessary to a candle and to fire see W. H."
We may conjecture that this note refers to Harvey's promised
treatise on respiration, which was never published.
So far Harvey has simply reiterated the ancient doctrine of cooling
and ventilation, as in the passages quoted previously from the
treatise of 1628. We shall find it very interesting to see how he
deals with the other ancient doctrine that some of the substance
of the air joins the blood in respiration. That this is true, gas
analysis and the mercurial air-pump have taught us; but in this
matter modern demonstration does but confirm, extend, and make
precise one of the oldest of physiological beliefs. Regarding this
we must now give the floor once again to the ancients, in order to
make Harvey comprehensible.
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
aërial 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
aëreal 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 preëminence, 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 aëreal or rendered more
vaporous; as though there were no spirits not aëreal, 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?