By no means in accord with the cause of the heart-beat first advocated by Harvey in 1649, is an experiment which he himself had brought forward in support of the circulation in 1628. In the famous treatise of that year he tells us that if the vena cava of a living snake be compressed at a point some distance away from the heart, the vein between that point and the heart is nearly emptied by the heart-beat, and the heart itself becomes paler and shrinks from lack of blood "and at length beats more languidly."[249] These words show that in this experiment the orderly heart-beats must have continued after the blood remaining in the vena cava had become too scanty to excite them by its expansion in accordance with his doctrine. It is, therefore, an interesting question how Harvey could reconcile the beating of the empty heart with his belief as to the "prime efficient cause" of its beat.
It may seem surprising that the discoverer of the venous return felt the need of a deus ex machina to distend the right auricle. On reflection, however, ought it to surprise us that, although we find the muscular power of the heart sufficient to complete the Harveian circulation, Harvey himself did not, but eked it out with Aristotelian forces? Vigorous as Harvey was, he could not make smooth the road which he himself had broken. For instance, he could not study, like ourselves, the return of the blood to the heart in the opened chest of an animal anæsthetized and curarized. The knowledge gained by his own tireless investigations did not suffice to teach him what we now know, viz.: that the unaided force of the systole of the left ventricle is sufficient to distend the right auricle with blood and to charge with blood the right ventricle as well.
The essence of Harvey's great discovery is his reversal of the immemorial direction of the venous flow, which he also proved to be abundant and rapid. But the laws which rule this flow were not, and could not be, patent to him as to us, owing to the imperfect physiological knowledge of his day. Hence at times his statements as to the movement of the blood are conceived in what, to borrow an architectural phrase, may be called a "transition style." As a sequel to his doctrine of the cause of the heart-beat let us pass in review some of these statements; but, first, let us briefly note a few facts which may help us to realize the imperfect state of the science of physics in Harvey's day.
Harvey was fourteen years younger than Galileo, who struck crippling blows at the Aristotelian physics, yet could not explain the common pump;[250] and Harvey's discovery of the circulation was made public thirteen years before the momentous work on the movement of liquids done by Torricelli, who was thirty years younger than Harvey.[250] Moreover, it was only a year before the publication of the Exercises to Riolanus in Harvey's old age that Blaise Pascal supplied the final proof that the mercurial column below the vacuum of Torricelli's barometer is really sustained by the pressure of the atmosphere.[250] It was not till one hundred years after the publication of Harvey's discovery that the Reverend Stephen Hales published the first comparative manometric measurements of the blood-pressure in the arteries and the veins of the same living animal, and stated in his preface that "the animal fluids move by Hydraulick and Hydrostatical Laws."[251]
Now let us turn to some delineations of the movement of the blood made by Harvey himself. I have found no evidence that he knew the venous flow to be promoted by the aspiration of the chest; but he knew well the effect of the muscular movements of the body upon that flow. Of course he had a perfect grasp of the fundamental truth that the main cause of the venous return is the forcible emptying of the ventricles into the arteries. He says to Riolanus:—
"Among these things should be noted the force and violence and rapid vehemence which we perceive by touch and sight in the heart and greater arteries; and the systole and diastole of the pulse in the larger and warmer animals I do not affirm to be the same in all the vessels which contain blood, nor in all blood-containing animals; but to be such and so ample in all that as a result thereof a streaming and an accelerated course of the blood through the small arteries, the porosities of the parts, and the branches of all the veins are necessarily brought about; and as a result thereof a circulation....[252] In the case of the arteries, over and above the shock, pulse, or vibration of the blood (which is not equally perceptible in all), a continual flow and movement thence take place until the blood returns to the point whence it started first, namely, the right auricle."[253]
The Title-page of William Harvey's Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, Frankfort, 1628.
With the calm quantitative account which a reader of Hales' "Statical Essays" will find given by that clergyman of his epoch-making physical experiments upon the blood-pressure, it is interesting to compare the following vivid qualitative recital of inferences made from surgical observations by his great predecessor. Harvey says:—
"Moreover, whoever shall have seen and thought upon the amount of difficulty and exertion with which the blood is stanched by compression, ligatures, or various appliances, when it leaps impetuously out of a petty artery, even the smallest, which has been cut or torn in two; and shall have seen or thought upon the amount of force with which the blood, as though thrown out from a syringe, flings off and drives before it the whole of the appliances, or traverses them—that man will hardly believe it probable, I think, that any of the blood can pass backward against so great an impulse and influx of the entering blood, unless from a point whence it is driven back with equal force."[254]
Harvey rightly discountenanced the ancient idea of direct anastomoses between the mouths of veins and the mouths of arteries, as opposed to fine and multiplied communications. In some situations, however, he admitted that ampler communications exist comparable to such anastomoses; and it throws light upon his state of mind as to the movement of the blood that, despite his recognition of the very forcible exit of the blood from the arteries, he suggested in his old age that in the cases aforesaid regurgitation from vein to artery is guarded against by a valvular arrangement, the terminal part of the artery traversing the wall of the vein obliquely, as the ureter traverses the wall of the bladder and as the biliary duct traverses the wall of the duodenum.[255] We should not forget that in his day the capillary vessels, the existence of the corpuscles, and the chemistry of the blood were still unknown; so that the passage into the veins of the mysterious hot vital liquid through the "porosities" of the parts might naturally present itself to his mind in a way very strange to us. He tells us this:—
"The blood does not take its course through the looser texture of flesh and parenchyma in the same way as through the more compact consistency of tendinous parts. Indeed, the thinner and purer and more spirituous part passes through more quickly; the thicker, more earthy, ill-composed[256] part tarries longer and is rejected."[257]
After more than twenty years of the comment and criticism, called forth by his treatise of 1628, he said to Riolanus:—
"As to whether the moving blood be attracted, or impelled, or move itself by virtue of its own intrinsic nature, enough has been said in my little book on the motion of the heart and blood."[258]
Yet about two years after the Exercises to Riolanus, Harvey, in writing a private letter, judged it necessary to accentuate, as follows, his denial that forces of attraction really play the part in physiology which the ancients had conceded to them. Speaking of the impulsion of the blood through the arteries, he says:—
"Indeed, the passage of the blood into the veins is brought about by that impulsion and not by any dilatation of the veins whereby, like bellows, they draw in the blood."[259]
But, despite the foregoing utterances and other such, his statements are sometimes vague and sometimes quite unexpected, regarding the nature of the movement of the blood in the veins. Indeed, in 1628 he speaks quite as a disciple of Aristotle. He says regarding the flow in the arteries:—
"For this distribution and movement of the blood there is need of impetus and violence and of an impeller such as the heart. Partly because the blood readily concentrates and gathers together of itself—toward its seat of origin, as it were,[260] or as a part to the whole, or as a drop of the water sprinkled upon a table to the mass thereof—as the blood habitually and very speedily does from slight causes, from cold, fear, horror, and other causes of this sort; partly, also, because the blood is pressed out of the capillary veins into the small branches and thence into the greater by the movements of the limbs and the compression of the muscles; the blood is more disposed and prone to move from the circumference on the center than the other way, even supposing no valves to be present as a hindrance. In order, therefore, to relinquish its seat of origin, and enter constricted and colder places, and move in opposition to its bent,[261] the blood has need not only of violence but of an impeller, such as is the heart alone, and after the fashion described already."[262]
This picture of the blood hesitating to leave its warm cardiac birthplace for the chill regions of the periphery, but very ready to return, has a tone far from hydraulic, but may so much the better prepare us for the view, made public by Harvey in his old age, that the blood is the primal seat of the soul itself. Except in the light of the foregoing passage the following words would be quite obscure. He says that the auricles
With due allowance for the use of modes of expression no longer familiar we find Harvey in 1649 handling the venous flow with no very modern touch, in the following passage—a passage which also reminds us that not till twelve years later, four years after Harvey's death, did Malpighi announce his discovery of the capillary blood-vessels in the lung of the frog.[265] Harvey says to Riolanus:—
"The arteries are never depleted except into the veins or the porosities of the parts, but are continually stuffed full by the pulse of the heart; but in the vena cava and the circulatory vessels, into which the blood glides at a quick pace and hastens toward the heart, there would be the greatest scarcity of blood, did not all the parts incessantly pour out again the blood poured into them. Add, also, that the impetus of the blood which is urged and driven at every pulsation into all parts of the second and third regions, forces the blood contained therein from the porosities into the little veins and from the branches into the larger vessels; this being effected also by the motion and compression of the surrounding parts; for contents are squeezed out of whatever contains them, when it is compressed and narrowed. So by the movements of the muscles and limbs the venous branches which creep on between are pressed upon and narrowed, and push on the blood from the lesser toward the greater."[266]
A similar touch of vagueness is perceptible when the venous flow is dealt with by Harvey in that very same résumé of the circulation which seats the underlying cause of the pulse in the hot blood of the vena cava close to the auricle. In that résumé he says to Riolanus:—
"I assert, further, that the blood in the veins courses always and everywhere from the lesser into the greater and hastens from all parts toward the heart; whence I gather that the amount, continuously sent into the arteries, which the arteries have received is transferred through the veins, and at length returns and flows back whence it first was impelled; and that in this wise the blood is moved in a circle in flux and reflux by the heart, by an impulsion the impetus of which forces the blood through all the arterial filaments; and that afterward in a continuous flow from all parts it goes back through the veins, one after another, by which it is absorbed, drained away, and transported."[267]
As to the flow in the lungs Harvey says in the treatise of 1628:—
"It being the will of nature that the blood itself be strained through the lungs, she was obliged to superadd the right ventricle, in order that by the beat thereof the blood might be driven through the lungs themselves, out of the vena cava into the cavity of the left ventricle."[268]
We have already found Harvey saying to Riolanus, in regard to the pulmonary transit, that the blood within the branches of the arterial vein
"cannot now go back in opposition to the sigmoid valve, while at the same time the lungs are widened and enlarged and then narrowed, by inspiration and expiration, and with the lungs their vessels also, and offer to the blood aforesaid a path and transit into the venous artery."[269]
More than thirty-two years earlier Harvey had written in his note-book the following words:—
"N.B. The lungs by their movement in subsiding propel blood from the arterial vein into the venous artery and thence into the left auricle."[270]
When we review and ponder the foregoing delineations of the character of the movement of the blood, we may cease to wonder that Harvey did not recognize the simple hydraulic cause of the distention of the right auricle and felt obliged to seek a more recondite explanation thereof, finding this in an Aristotelian expansion of the hot blood.
No doctrine of Harvey sounds stranger to a biologist of to-day than his doctrine that the blood is the seat of the soul; nor does any other belief of the great discoverer reveal him more clearly to be a link between the old and the new; not simply an innovator who fixed a gulf between them. We have heard him explicitly deny in his old age the Aristotelian doctrine that the heart "is endowed with soul." We have seen that thirty-five years earlier he had jotted down in his note-book these words: "The soul is in the blood."[271] Let us study him now as he lays stress, not merely on the primacy of the blood, but on its psychological endowments.
Thirteen years before the date of Harvey's note-book Shakspere's play of "Hamlet" had appeared in print; in which the prince speaks thus of following his father's ghost:—
It has been foreshadowed that for Harvey, the graduate of Cambridge and of Padua, the physician of the Renaissance, the word "anima"—"soul"—did not simply mean the immortal part of man, as for Hamlet, but was equivalent to the "psyche" of ancient philosophy. In order, therefore, readily to follow Harvey's thought at this juncture, we must first, like him, go to the fountain head; for only sayings of Aristotle can give us a sufficient clue to what he, and after him Harvey, meant by "soul."
Aristotle says in his treatise On Soul:—
"Some natural bodies have life and some have not. By life we mean the being nourished, and growing, and decaying, of oneself."
In the same treatise he says further:—
"The soul is that by which primarily we are alive, and display sensation and intellect; ... but it is not matter and substratum."
Again he says:—
"Were the eye an animal, vision would be the soul thereof; for reason indicates that vision is the essence of the eye.[273] The eye in its turn is the material [basis] of vision; which latter failing, the eye is not an eye except in name, like an eye of stone or in a drawing."
The doctrines of the foregoing three passages are developed and made more explicit in the following, still from the treatise On Soul:—
"It is the presence of life, we say, which makes the difference between that which has soul and that which has not. To amplify regarding life: we call anything alive which possesses even a single one of the following: intellect, sensation, motion and rest in space, and also the motion[274] involved in nutrition, and both decay and growth. Therefore, even all the plants are held to be alive."
A few lines further on Aristotle says, speaking of the power or faculty[275] of taking nourishment:—
"This can exist without the others, but not the other faculties without this, in mortal beings. The aforesaid is clear in the case of plants; for they possess no other faculty of the soul. To this faculty then life owes its origin in living things; but the being an animal owes its origin primarily to sensation; for beings that neither move nor change their place but yet possess sensation, we call animals and not merely living things. The primary sense, which exists in all, is touch; and just as the nutritive faculty can exist without touch or sensation of any kind, so can touch exist without the other senses. The "nutritive" is our term for such part of the soul as is shared even by plants, all animals, however, evidently possessing the sense of touch. The cause of the presence of each of the two aforesaid shall be told later. Now let us only go so far as to say that the soul is the source of the [faculties] aforesaid, and is defined by means of them, to wit: the nutritive, the sensory, the intellectual, the motor.[276] As to whether each of these is a soul or is a part of the soul; and if a part, whether in the sense that it is only separable by reasoning,[277] or locally as well—as to some of these points, it is not hard to see our way, but some present difficulties."[278]
If we turn to Aristotle's treatise On Generation we find him dealing with the relations of the body to the nutritive soul, in virtue whereof the body is alive; with its relations to the sensory soul, in virtue whereof it is an animal body; and, finally, in man with its relations to the intellectual soul. Of these three kinds of soul or parts of the soul, he concludes, the mind "is alone divine; for in the working thereof no bodily working is involved."[279] Only soul of this divine quality does he admit to be separable from body.[280]
The master has spoken. Now let the great pupil speak. In the last Exercise but one of his treatise On Generation, Harvey says, referring to the blood:—
"It assuredly contains the soul first and foremost, not only the nutritive, but the sensory soul as well, and the motor. The blood penetrates in all directions and is present everywhere; if it be taken away, the soul itself is made away with also and at once; so that the blood would seem to be wholly indistinguishable from the soul or, at least, should be reckoned the substance of which the soul is the activity. The soul I aver to be such that neither is it body at all, nor yet entirely without body, but comes in part from without, in part is born on the premises,[281] and in a manner is part of the body; in a manner, however, is the origin and cause of everything within the body of an animal, certainly of nutrition, sense, and motion, and hence, in like manner, of life and death; for whatsoever is nourished, that same is living, and vice versa. So, likewise, whatsoever is nourished abundantly, increases; but whatsoever too sparingly, dwindles; and whatsoever is nourished perfectly, keeps its health; whatsoever otherwise, lapses into disease. Therefore, as is the soul, so also is the blood to be reckoned the cause and author of youth and old age, of sleep and of waking, and even of respiration also—especially in view of this, that in the things of nature the first instrument contains within itself an internal moving cause. Therefore, it comes to the same whether one say that the soul and the blood, or the blood together with the soul, or, if preferred, the soul together with the blood, bring everything within an animal to pass."[282]
Only two years before these words were published the aged Harvey had said the following:—
"Nor does the blood possess vigor, faculty, reason, motion, or heat, as the gift of the heart."[283]
A comparison of the foregoing passages from Harvey with the preceding passages from Aristotle makes it clear that, for Harvey, although the soul dwells no longer in its Aristotelian seat, it is no other than the Aristotelian soul which pervades the "principal part" of the body, the living blood of the Harveian circulation.
What proofs does Harvey offer that the soul is in the blood? He has offered already one weighty piece of evidence noted by many from of old in the chase, in butchery, in sacrifice, in battle—the evidence from fatal hæmorrhage. This had been set forth nineteen centuries before him by one of his Hippocratic predecessors, who had referred to the reasoning
"used by those who say that the blood is the man; for, seeing men slaughtered and the blood running out of the body, they conclude that the blood is the soul of man."[284]
Presently Harvey himself shall tell us that in placing the soul in the blood he is consciously reaffirming one of the most ancient of beliefs; but he is far from basing his adhesion to it merely on such immemorial evidence, known to all, as the result of loss of blood, for he also adduces once more his own observations of the early embryo of the fowl, to prove not only the primacy of the blood but the presence of the soul therein. His testimony follows, and in reading it one must bear carefully in mind that in Harvey's time no clear scientific distinction had yet been worked out between movements which imply sensation, and movements, whether reflex or not, which do not depend upon consciousness. In his treatise On Generation Harvey says:—
"For my own part I am sure from numerous experiments that not only motion is inherent in the leaping point,—which no one denies—but sensation also. For you will see this point thrown into varied commotion and, as it were, irritated, at any touch whatever, even the slightest, just as sensitive bodies in general usually give evidence of sensation by movements proper to themselves. Moreover, if the injury be repeated often, the leaping point becomes excited and the rhythm and order of its pulsations disturbed. In like manner do we infer the presence of sensation in the so-called sensitive plant and in zoöphytes, from the fact that when they are touched they draw themselves together as though taking it ill.... So there is no doubt that the leaping point lives, moves, and feels like an animal."[285]
In a later part of the same treatise he says:—
"It is manifest that all motion and sensation do not proceed from the brain, since we plainly perceive the presence of motion and sensation before the brain has come into existence; what I have related proves that clearly sensation and motion dawn forthwith in the first droplet of blood in the egg, before a vestige of the body has been formed. Moreover, in that first state of the structure or constitution of the body which I have called the mucilaginous, before any members are discernible and when the brain is nothing but limpid water, if the body be only lightly pricked it moves, contracts, and twists itself obscurely like a worm or caterpillar; so that it gives clear evidence of sensation."[286]
In another Exercise of the same treatise he says:—
"It is evident also from the generation of the chick, that whatever the source of its life or the vegetative first cause of it may be, this had a prior existence in the heart. Wherefore, if the said first cause be itself the soul of the chick, it stands proved likewise that this had a prior existence in the leaping point and the blood; seeing that we observe therein motion and sensation; for it moves and leaps like an animal. If, then, there exist in the leaping point the soul, which (as I have taught in my account) constructs for itself the rest of the body, nourishes and increases it, certainly from the heart as from a fount the soul flows out[287] into the entire body.
"So, likewise, if the egg be prolific because there is a soul in it, or (as Aristotle would have it) the vegetative part of the soul, it is clearly proved that the leaping point, in other words the generative part endowed with soul, springs from the soul of the egg, for nothing is the author of itself, and that the soul is transferred from the egg to the leaping point, next to the heart, and then to the chick."[288]
In still another chapter of his treatise On Generation Harvey says:—
"Nor does the blood deserve to be called the original[289] part and the principal part, merely because in it and by it motion and pulsation are originated, but also because in the blood the psychical heat first comes into existence, the vital spirits are generated, and the soul itself inheres. For wherever the immediate and principal instrument of the vegetative faculty is first found, there probably the soul also is first present and takes its origin thence; since the soul is inseparable from the spirits and the innate heat....[290]
"The life then inheres in the blood (as we read also in Holy Writ),[291] because therein the life and the soul are manifest first and fail last....[292]
"It stands clearly proved that the blood is a generative part, the source of life, the first to live and the last to die, the primary seat of the soul; that in the blood, as in its source, the heat first and chiefly abounds and flourishes; and that by and from the blood all the other parts of the whole body are fostered and obtain their life by means of the influx of heat. Indeed, the heat which accompanies the blood floods, fosters, and preserves the entire body, as I have demonstrated already in my book on the motion of the blood."[293]
Harvey's proof that the blood is "the first to live and the last to die," we have scanned already in an earlier chapter of this paper. In the next chapter of his treatise On Generation he says:—
"No heat is to be found, either innate or inflowing, other than the blood, to be the soul's immediate instrument."[294]
On the next page, after briefly making certain suppositions, he says further:—
"Why should we not affirm with equal reason that there is soul in the blood; and also, since the blood is the first thing generated, nourished, and moved, that out of the blood the soul is first evoked and kindled? Certainly it is the blood in which vegetative and sensitive workings first come to light; in which heat, the primary and immediate instrument of the soul, is innate; it is the blood which is the common bond of body and soul, and in which as a vehicle soul flows into all parts of the whole body."[295]
But no matter how far on high the blood may have been exalted by Harvey the physician and psychologist, it is still subject to the lancet of Harvey the clinician, the heir of Hippocrates; for in his treatise On Generation, in the same Exercise with the foregoing passage, occurs the following:—
"While I assert that the seat of the soul is in the blood, first and foremost, I would not have the false conclusion drawn from this that all blood-letting is dangerous or hurtful; nor have it believed, as the multitude believes, that just to the degree that the blood is taken away does the life pass away at the same time, because holy scripture has placed the life in the blood. For it is known from everyday experience that the taking of blood is a wholesome aid against very many diseases and is chief among the universal remedies; seeing that depravity of the blood, or excess thereof, is at the bottom of a very great host of diseases; and that the timely evacuation of blood often brings exemption from most dangerous diseases and even from death itself. For just to the degree that the blood is taken away as our art prescribes, is an addition made to life and health. This very thing has been taught us by Nature, whom physicians set themselves to imitate; for Nature often makes away with the gravest affections by means of a large and critical evacuation by the nares, by menstruation, or by hæmorrhoids."[296]
Not only does Harvey affirm that "the soul is in the blood" and, as we have seen, appeal to observation and experiment in support of this doctrine; but he refers to those who had believed it before him, and maintains it against Aristotle's express denial. We have heard him testify as an observer; now let us hear him deal historically and polemically with the doctrine in question. Quite simply, in the final work of his old age, does the veteran tell of the wide acclaim which at last has greeted his discovery of the circulation—the most modern and revolutionary achievement of his time. The contrast is startling when, in the same breath, with equal simplicity he proceeds formally to identify his own latest view of the significance of the circulating blood with a doctrine which had been ancient in ancient times; a doctrine not only found in the Old Testament, but held by Greek thinkers who were historic figures even in the eyes of Aristotle. In his treatise On Generation Harvey says:—
"I see that the admirable circulation of the blood which I discovered long ago has proved satisfactory to nearly all, and that so far no one has made any objection to it which greatly calls for answer. Therefore, if I shall add the causes and uses of the circulation and reveal other secrets of the blood, showing how much it conduces to mortal happiness and to the welfare of soul as well as body, that the blood be kept pure and sweet by a right regimen, I truly believe that I shall do a work as useful and grateful to philosophers and physicians as it will be new; and that the following view will seem to nobody so improbable and absurd as it formerly seemed to Aristotle, viz.: that the blood, a domestic deity as it were, is the very soul within the body, as Critias and others thought of old; they 'believing that capacity for sensation is the most special attribute of the soul, and exists because of the nature of the blood.' By others again that which derives from its own nature the power of causing motion was held to be the soul; as Thales, Diogenes, Heraclitus, Alcmæon, and others believed.[297] It is made plain, however, by very numerous signs that both sensation and motion inhere in the blood in spite of Aristotle's[298] denial."[299]
We have noted with Harvey the doctrine of Leviticus, which still rules the procedure of the Jewish butcher; and as we look backward to Athens across the centuries, we find Plato putting this question into the mouth of Socrates: "Whether it be the blood with which we think, or air, or fire, or none of these."[300] In Hellas this doctrine had been well known before Plato, Socrates, or the Hippocratic writers, one of whom we have found referring to it. The Sicilian Greek Empedocles, a philosopher and physician born at Acragas about 495 B.C., is said to have held, long before Aristotle, that the heart is the part formed first in the embryo;[301] and in a line of verse which has come down to us Empedocles said: "In the blood about man's heart is his understanding."[302] Empedocles is reported to have held to this because in the blood "are most perfectly blended the elements of the parts,"[303] that is, earth, water, air, and fire.
The accomplished and wicked Athenian Critias, to whom Harvey refers, was that chief of the Thirty Tyrants who was slain in 403 B.C., four years before Socrates drank the hemlock and nineteen years before the birth of Aristotle. With the opinion of "Critias and others" Harvey, as we have seen, identifies his own view that the soul is in the blood. They held capacity for sensation to be the mark of soul and to be due to the nature of the blood; and Harvey's statement of these views is a literal quotation from the second chapter of the first book of Aristotle's treatise On Soul, which Harvey cites. This chapter is also the source of his summary and not quite exact reference to those other ancients who, as he avers, held spontaneous motor power to be the mark of soul—a power which Harvey unites in the blood with capacity for sensation.[304]
In the aforesaid chapter of Aristotle's work On Soul this philosopher had curtly reckoned among the "cruder" thinkers those of his predecessors who, "like Critias," had held the soul to be blood. Harvey notes the master's condemnation, but, as we have seen, stoutly ranges himself with the condemned ancients and affirms that sensation is inherent in the blood despite the master's denial. It is strange to note how the London physician seems less modern, for the moment, than the ancient philosopher of Athens. Aristotle, like a man of to-day, treats the blood simply as the immediate food of the tissues, noting expressly that it has "no feeling when touched in any animal, just as the excrement in the belly has no feeling."[305] Harvey deals as follows with this obvious truth in dealing with the question whether the blood can properly be reckoned a part of the body in the technical sense. He says:—
"At this time I will only say this: Even if we concede that the blood does not feel, nevertheless, it does not follow that it is not a part of a sensitive body and the principal part at that."[306]
We do not know that Aristotle ever saw or noted in the dying auricle the "undulation" by which Harvey was so much impressed; but we have seen that, like Harvey, Aristotle treated of the development of the early embryo within the hen's egg and that, like Harvey, he laid special stress upon the red "leaping point." Aristotle concluded that the heart is the first generated living part, that it makes and will make throughout life the blood which it contains and distributes. In the heart he fixed the focus of the innate heat and, knowing nothing of the nervous system, he fixed in the heart the seat of the soul also. Harvey came to the conclusion that the blood is the first generated living part; that it has made the heart which contains it and which keeps it circulating and which it will nourish throughout life, as it will the other parts. In the blood itself he placed the innate heat and, though he knew the nervous system, he placed in the circulating blood the seat of the soul, which animates every part.
"We conclude," he says, "that the blood lives and is nourished of itself and in no wise depends upon any other bodily part either prior to or more excellent than itself."[307]
Thus the rigorously proved and demonstrated circulation of the blood was linked by its discoverer with the speculations of remote antiquity.
As we have seen, the use of the circulation became to Harvey a life-long subject of speculation, because this discovery had raised questions which no man could answer before the finding of oxygen. How obscure a problem Harvey found the functions of the blood to be, is nowhere better indicated than where he says in his old age:—
"So with better right one might maintain that the blood is equally the material of the body and its preserver, but not merely its food. For it is well known that in animals that perish of hunger, and also in men who waste away and die, there is abundance of blood to be found in the vessels, even after death."[308]
Is it the least part of Harvey's glory that his mind had cloven its way through long-lived beliefs to a truth which he could demonstrate but could not explain, and which seemed to other eminent men to be no truth, because too senseless to be true?[309] When he finally broke with the ancient master, Harvey could not be content with sheer ignorance; and the same observations and experiments which led him out of Aristotelian error misled him into error quite as grave. As to the venerable doctrine regarding the seat of the soul, which he at last embraced upon grounds now seen to be too slender, was not this doctrine one with which the Harveian circulation could harmonize well and which in turn could greatly glorify the circulation? Let us pause, think, and read further.
The latter part of Harvey's treatise On Generation is devoted to that of the mammal; but the treatise does not end with the end of this subject, for from his account of generation the author turns abruptly to append two Exercises on other topics. The first of these two is entitled "On the Innate Heat," and the second, which is very brief, is entitled "On the Primitive Moisture."
The Exercise On the Innate Heat is Harvey's express and polemical contribution to this subject, which had been much discussed both during and before his time;[310] a subject with which the famous discoverer deals roundly by maintaining that the innate heat is neither more nor less than the circulating blood. So the last words as to the significance of the circulating blood which he wrote for publication are contained in this Exercise. It begins as follows:—
"Since mention is often made of the innate heat, I propose now, by way of dessert, briefly to discuss the same and the primitive moisture also; and this the more willingly that I see there are many who take the greatest delight in those names and yet, in my judgment, comprehend but little of the things themselves. Truly, there is no need to seek for any spirits distinct from the blood, or to bring in heat from elsewhere, or call gods upon the stage and load philosophy with fanciful opinions; for what we so commonly would fetch from the stars is born at home. In truth, the blood alone is the innate warmth, or the first-born psychical heat;[311] as is proved excellently well by our observations of the generation of animals, especially of the chick in the egg; so that it were superfluous to multiply entities. Indeed, there is nothing to be met with in the animal body prior to the blood, or more excellent; nor are the spirits which they distinguish from the blood to be found anywhere separate from it; for the very blood itself, if without spirits or heat, does not deserve the name of blood, but of cruor....
"Scaliger, Fernelius, and others lay less weight on the extraordinary endowments of the blood and imagine other spirits to exist, aërial or ethereal or composed of substance both ethereal and elemental, constituting an innate heat more excellent and more divine, as it were; and these spirits they believe to be the soul's most immediate instrument, the fittest for every use. They rely especially upon this argument, viz.: that the blood, being composed of elements, can exert no activity beyond the powers of the elements or of bodies consisting of a mixture thereof. Therefore, they imagine a spirit, another innate heat, of celestial origin and nature, to wit: a body most simple, most subtile, most fine, most mobile, most swift, most clear, ethereal, and sharing in the quintessence. Nowhere, however, has any such gift of spirit been demonstrated by them, nor that the same acts beyond the powers of the elements, or accomplishes greater works than could the blood alone. As for us who use our senses to guide us in the scrutiny of things, nowhere have we been able to find anything of the kind. Furthermore, there exist no cavities destined for the generation or preservation of these spirits, or even assigned thereto by the persons aforesaid."[312]
A little farther on we read:—
"I deem it, however, most wonderful that spirits which draw their origin from heaven and are adorned with such surpassing endowments should be nourished by our common and elemental air; especially seeing that their advocates hold that none of the elements can act beyond its own powers....[313] What need then is there, say I, of that foreign guest, ethereal heat, since all can be accomplished by the blood, even as by it; while from the blood the spirits cannot withdraw a hair's breadth without perishing? Most assuredly nowhere do they wander or penetrate as separate bodies without the blood. For whether it be said that they are generated, nourished, and increased from the thinner part of the blood, as some believe, or from the primitive moisture, as others hold; yet it is confessed that they are never found outside the blood but forever cleave to the same as to their sustenance, as flame does to oil or to a wick. Wherefore their tenuity, subtility, mobility, and so forth, confer no greater advantage than does the blood which they continually accompany. It follows that the blood suffices and is fit to be the immediate instrument of the soul, since the blood is present everywhere and most swiftly permeates hither and thither."[314]
The two opponents named by Harvey were not his contemporaries, but worthies of the Renaissance who had written about one hundred years before the publication of his treatise On Generation and had died before he was born. The Italian physician Julius Cæsar Scaliger had written learned commentaries on Aristotle, as well as other works; and the Frenchman Jean Fernel, physician to King Henri II of France, had taught anatomy at Paris and had been a medical writer of importance. Each of these two authors was nearly sixty years of age in 1543, in which memorable year were first published the revolutionary writings of the aged astronomer Copernicus and of the young anatomist Vesalius, in the second year after the death of the hardy innovator Paracelsus. Such were the men against whose doctrines Harvey was impelled in his old age to launch his vigorous criticism, in order to clear the way for his own doctrine of the preëminence of the blood. What can we workers of to-day make of their opinions, which were living for Harvey but now are so deeply buried? Test-tube and balance, telescope, spectroscope, microscope, manometer, and the rest, have served their purpose so well since Harvey's time that even he, one of the foremost worthies of science, must seem merely to beat the air with words in his last message to us, unless we can recover his standpoint. Happily he himself shall attempt to clarify the meaning of his polemic by setting before us certain words of Aristotle, embodying far-reaching speculations as to body and soul in relation to the universe. Yet we shall find these not easy to understand.
Let Harvey continue his criticism of his predecessors. He says:—
"But while they believe that there are found in animals spirits and ultimate or primitive nourishment, or something else, which acts beyond the powers of the elements more than does the blood, they do not seem to have a sufficient grasp of what it may be to 'act beyond the powers of the elements'; nor have they rightly interpreted the words of Aristotle where he says:[315] 'The virtue or potency of every soul[316] seems to be associated with a body[317] other than the so-called elements and more divine.'"
And a little farther on:[318]—
"'For there exists in the semen of all [animals] that which makes their semen generative, the so-called heat. Yet this is not fire, nor any such power, but the spirits[319] included in the semen and in foaminess, and in the spirits the nature which is analogous to the element of the stars.[320] Wherefore fire generates no animal, nor does anything [animal] appear in process of formation in that, whether moist or dry, which is undergoing the action of fire;[321] whereas the heat of the sun and that of animals—not only that [which acts] through the semen,[322] but also, should there occur some excretion of a different nature[323]—even this, too, possesses a life-giving principle. It is patent, then, from such [facts] as these that the heat in animals is not fire and does not take its origin from fire.'[324]
"I, too, would say the same, for my part, of the innate heat and the blood, to wit: that it is not fire and does not take its origin from fire, but is associated with another body and that more divine, and, therefore, does not act by reason of any elemental faculty; but, just as there exists in the semen something which makes it generative and exceeds the powers of the elements in building an animal—to wit, spirits, and in the spirits a nature analogous[325] to the element of the stars—so likewise in the blood there exist spirits or some power which acts beyond the powers of the elements, a power very conspicuous in the nourishing and preserving of the several parts of an animal; and in the spirits and blood exist a nature, yea, a soul, analogous to the element of the stars. It is manifest, therefore, that the heat in the blood of animals during life is not fire and does not take its origin from fire; and this is taught excellently well by our own observations....[326]
"Therefore, those who assert that nothing composed of the elements can work beyond the powers of these, unless it be associated at the same time with another body and that more divine, and maintain, therefore, that the spirits aforesaid consist in part of the elements, in part of some ethereal and celestial substance—truly, such persons seem to me to have drawn their conclusions ill. For you shall find scarcely any elemental body which, when in action, will not exceed its own proper powers."[327]
On reaching the end of the last quoted words of Harvey's polemic, a physician or biologist of to-day may easily be conscious of disappointment, even of a mild despair; for the once celebrated passage from Aristotle, about the interpretation of which Harvey gives battle, seems at first the source of all the obscurities of the controversy, rather than of the promised light which shall clear them away. Yet that light must come by way of that rugged passage. The gist of the first part of the Aristotelian passage may be set forth as follows: In the semen soul is potential, being associated therein with a "body" or "nature" which possesses a "life-giving principle" and is in the spirits, i.e., in the hot vapor, within the foam-bubbles of the semen. This body or nature is called heat, yet it is not that one of the four elemental bodies which is known as fire, nor yet a derivative of this, but is "a body other than the so-called elements and more divine," a "nature analogous to the element of the stars." What is this "element of the stars"? It is clear that only from the answer to this question can the light which we are seeking begin to shine. To find this celestial element we must immediately take a rapid glance at the Aristotelian universe—that grand conception which the master mainly accepted from his predecessors and contemporaries, but owed, in part, to the work of his own mind. Let us swiftly scan what he styled the "Cosmos."
At the center thereof is the earth, spherical and motionless. The core of the universe consists not only of this central globe with everything in or upon it, but also of the atmosphere or, more correctly, of all which extends between the surface of the globe and the nearest of the distant revolving hollow spheres of heaven, in some of which spheres are set the heavenly bodies. Below the heavenly spheres this core of the universe is made up of the four elements, earth, water, air, and fire; and all things composed of these are subject to opposed and limited and compounded motions, to generation, alteration, and corruption. The inclosing heaven, on the other hand, is unchangeable and eternal, has never been created, and will never be destroyed. Its many component hollow spheres are contiguous and concentric, and concentric also with our globe. In a single sphere, the outermost, called the "first heaven," all the fixed stars are set. In separate spheres, nearer to the earth, are set the seven bodies which the astronomy of Aristotle's day styled "planets." To these (here designated by their present names) that ancient astronomy assigned the following order from the earth outward toward the fixed stars: the moon, the sun, Venus, Mercury, Mars, Jupiter, and Saturn. Each of the celestial spheres revolves with simple circular motion in one direction forever. The "first heaven," the sphere of the fixed stars, needs but the one simple motion which is its own, and it carries with it in its daily revolution all the inner spheres. These are more numerous than the seven planets; for though each planet is set in but a single sphere, each planet's complex course results from the combined simple motions of more spheres than one. In spite of these more or less intimate relations, the spheres of heaven are separate existences, self-moved, like animals; and, like animals, possess activity, life, and soul. But the motion and life of the heavenly existences are continuous and eternal, and hence these existences—the spheres, and the planets and fixed stars set therein—are all divine; much more divine than man, though man possesses a far larger share of the divine than other animals.[328]
Just as the troubled regions which lie below the sphere of the moon are contrasted with the serene heaven which incloses and limits them, so the changing forms of matter which compose our globe and its nearer surroundings are contrasted with the simple unalterable substance of the heavenly spheres. "Of necessity," says Aristotle, "there exists a simple body whose very nature it is to be borne on in circular motion."[329] Elsewhere he says that the men of old "would seem to have assumed that the body which moves forever is likewise divine by nature."[330] This is "an embodied substance different from the compounds here, more divine and prior to them all";[331] a body "of a nature the more precious the farther it is withdrawn from what is here."[332] After reasoning about this body Aristotle says:—
"If what has been laid down be accepted, it is plain from the foregoing why the first of bodies is eternal, and shows neither growth nor decay nor old age nor alteration, and is affected by nothing. The conception seems to testify to the phenomena and the phenomena to the conception.... Therefore, as the first body is something different from earth and fire and air and water, [the ancients] gave the name of ether to the region most on high, naming it from its moving always during all eternity."[333]
The place in nature of "the first element," so grandly conceived, is fixed more definitely by Aristotle when he says "that the whole universe in the region of the courses on high is filled with that body."[334]
Now, therefore, we have attained the object of our rapid quest; at last we have reached "the element of the stars"; for Aristotle tells us that not only heaven, but all the heavenly bodies as well, consist of the ether, saying:—
"It is most reasonable and consequent, in view of things already said, for us to make each of the stars out of that body in which it has its course, since we have declared the existence of something of which the nature is to be borne in a circle."[335]
At a later day the ethereal element of the stars was distinguished from the four inferior elements not by its Aristotelian name of first element but by that of fifth element, or fifth existence, or fifth "essence." Hence arose and was applied to the fifth element the name "quintessence"; a word which in its turn acquired various meanings.
Ten years after Harvey's death Milton published his description of the creation of heaven; a description couched, however, in terms of the uncreated heaven of Aristotle. Milton wrote:—