Volume 1 — From The Fortnightly Review. THE HEART AND THE BRAIN. BY GEORGE HENRY LEWES.

Heart and brain are the two lords of life. In the metaphors of ordinary speech and in the stricter language of science, we use these terms to indicate two central powers, from which all motives radiate, to which all influences converge. They rule the moral and the physical life: the moral owes to them its continuous supply of feelings and ideas; the physical its continuous supply of food and stimulus. All the composite material which serves to build up the bodily fabric, and repair its daily waste, is only so much "carted material" awaiting the architect, until it has twice passed through the heart—until having been sent by the heart to the lungs it has there received its plastic virtues, and returns to the heart to be thence distributed throughout the organism. So much is familiar to every one; but less familiar is the fact that this transmission of the blood from heart to lungs, and its distribution throughout the organism, are rendered possible and made effective only under the influence of the brain. Life is sustained by food and stimulus. The operation of nutrition itself is indissolubly connected with sensibility. Life is a plexus of nutrition and sensation, the threads of which may ideally be separated, but which in reality are so interwoven as to be indissoluble. This is a paradox which even many physiologists will reject; but it is only a paradox because biological questions have constantly been regarded from a chemical point of view.

To render my proposition free from ambiguity, it is needful to premise that the term heart, by a familiar device of rhetoric, here expresses the whole of that great circulatory apparatus of which it is only a part; and in like manner the term brain here expresses the whole of the sensory apparatus. The reader knows perfectly well that in strict anatomical language the heart is only one organ having a definite function; and that the brain—although the term is used with considerable laxity—is only one portion of the complex nervous mechanism, having also its definite functions. But I am not here addressing anatomists, and for purposes of simplification I shall generally speak of the heart as if it were the whole of the vascular system, and of the brain as if it were the whole of the nervous system. And there is a philosophic truth suggested by this departure from the limitations of anatomical definition, namely, that if the brain as a nervous centre requires to be distinguished from all other nervous centres, it also requires to be affiliated on them: it has its special functions as an organ, but it has also a community of property—i.e., sensibility—with all other nervous centres.

In the study of animal organisms, the scientific artifice called analysis, which separates ideally what nature has indissolubly united, isolating each portion of a complex whole to study it undisturbed by the influences of other portions, has established a division of life into animal and vegetable. The division is as old as Aristotle, but has become the common property of science only since the days of Bichat. It is not exact, but it is convenient. As an artifice it has proved its utility, but like all such distinctions it has a tendency to divert the mind from contemplation of the real synthesis of nature. Even as an artifice the classification is not free from ambiguities; and perhaps it would be less exceptionable if {624} instead of vegetal and animal we were to substitute nutritive and sensitive. All the phenomena of growth, development, and decay—phenomena common to plants as to animals—may range under the laws of nutrition. All the phenomena of feeling and motion which specially distinguish animals, will range under the laws of sensibility. Plants, it is true, manifest motion, some few of them even locomotion; but in them it is believed that these phenomena are never due to the stimulus of sensibility.

Viewing the animal organism as thus differentiated, we see on the one hand a complex system of organs—glands, membranes, vessels—all harmoniously working to one end, which is to build up the body, and silently repair its continual waste. They evolve the successive phases of development. They prepare successive generations. On the other hand, we see a complex system of organs—muscles, tendons, bones, nerves, and nerve-centres—also harmoniously co-operative. They stimulate the organs of nutrition. They work first for the preservation of the individual in the struggle of existence; next, for the perfection of the individual in the development of his highest qualities.

But it is important to remember that this division is purely ideal—a scientific artifice, not a reality. Nature knows of none such. In the organism the two lives are one. The two systems interlace, interpenetrate each other, so that the slightest modification of the one is followed by a corresponding change in the other. The brain is nourished by the heart, and were it not for the blood which is momently pumped into it by the heart, its sensibility would vanish. And the heart in turn depends upon the brain, not for food, but for stimulus, for motive power, without which food is inert. That we may feel, it is necessary we should feed; that we may feed, it is necessary we should feel. Nutrition cannot be dissociated from sensation. The blood which nourishes the brain, giving it impulse and sustaining power, could never have become arterial blood, could never have reached the brain, had not the heart which sent it there been subjected to influences from the brain. The blood itself has no locomotive impulse. The heart has no spontaneous power: it is a muscle, and like all other muscles must be stimulated into activity. Unless the sensitive mechanism were in action, the lungs could not expand, the blood would not become oxygenated, the heart would not pump. Look on the corpse from which the life has just vanished. Why is it inert? There is food within it. It has blood in abundance. There is air in the lungs. The muscles are contractile, and the tendons elastic. So little is the wondrous mechanism impaired, that if by any means we could supply a stimulus to awaken the dormant sensibility, the chest would expand, the heart would beat, the blood would circulate, the corpse would revive.

It is unnecessary to point out in detail how dependent the brain is upon the heart; but mention may be made of the fact that more blood is sent to the brain than to any other organ in the body: according to some estimates a fifth of the whole, according to others a third. Not only is a large quantity of blood demanded for the continuous activity of the brain, but such is the peculiar nature of this great nervous centre, that of all organs it is the most delicately susceptible to every variation in the quality of the blood sent to it. If the heart pumps feebly, the brain acts feebly. If the blood be vitiated, the brain is lethargic; and when the brain is lethargic, the heart is weak. Thus do the two great centres interact. They are both lords of life, and both mutually indispensable.

There are two objections which it may be well to anticipate: Nutrition, it may be objected, cannot be so indissolubly blended with sensation as I have affirmed, because, in the first place, most of the nutritive processes go on without the intervention of {625} sensibility; and in the second place, the nutritive life of plants is confessedly independent of sensation, since in plants there is no sensitive mechanism whatever. Nutrition is simply a chemical process.

The answers to these objections may be very brief. Nutrition is a biological not a chemical process: it involves the operation of chemical laws, but these laws are themselves subordinated to physiological laws; and one of these laws is the necessary dependence of organic activity on a nervous mechanism wherever such a mechanism exists. Although popular language, and the mistaken views (as I conceive) of physiologists, allow us to say, without any apparent absurdity, that the processes of respiration, digestion, circulation, and secretion go on without feeling or sensation—because these processes do not habitually become distinct in consciousness, but are merged in the general feeling of existence—we have only to replace the word feeling, or sensation, by the phrase "nervous influence," and it then becomes a serious biological error to speak of nutrition as dissociated from the stimulus of nervous centres, as capable of continuance without the intervention of sensibility. The chemical combinations and decompositions do not of course depend on this intervention, but the transport of materials does. All the disputes which have been waged on this subject would have been silenced had the disputants borne in mind this distinction between the chemical and organic elements in every nutritive process. It is not the stoker who makes the steam; but if the stoker were not to supply the fire with coals, and the safety-valve were not to regulate the amount of pressure, steam might indeed be generated, but no steam-engine would perform its useful work. In like manner, it is not the vascular system which makes a secretion; but if the blood did not supply the gland with materials, the secreting process would quickly end, and the blood can only be brought to the gland through the agency of muscular contractions stimulated by nervous influence.

Granting that plants have no sensibility, and that in them the process of nutrition must go on without such an intervention, we are able to demonstrate that in animals in whose organism the sensitive apparatus is an integral portion, the processes of nutrition are more or less under the influence of this apparatus. In saying "more or less," I indicate the greater or less perfection of the organism; for, as every one knows, the perfection of each type is due to the predominance of its sensitive mechanism. In some of the lowest types, no trace of a nervous mechanism can be discovered. A little higher in the scale, the mechanism is very slight and simple. Still higher, it becomes complex and important. It culminates in man. Corresponding with this scale of complexity in the sensitive life is the scale of complexity in the nutritive life. As the two rise in importance they rise in the scale of dependence. Thus a frog or a triton will live long after its brain is removed. I have kept frogs for several weeks without their brains, and tritons without their heads. Redi, the illustrious Italian naturalist, kept a turtle alive five months after the removal of its brain. Now it is needless to say that in higher animals death would rapidly follow the loss of the brain. A somewhat similar parallelism is seen on the removal of the heart. None of the higher animals can survive a serious injury to the heart; but that organ may be removed from a reptile, and the animal will crawl away seemingly as lively as ever. A frog will live several hours without a heart, and will hop, swim, and struggle as if uninjured. Stilling once removed all the viscera from a frog, which, however, continued for one hour to hop, defend itself, and in various ways manifest its vivacity. [Footnote 124]

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In spite of these evidences of a temporary independence of brain and heart, as individual organs, there is nothing more certain than the intimate interdependence of the sensitive and circulating systems; and if in lower animals the interdependence of the two great central organs is less energetic than in the higher, the law of the intervention of sensibility in all processes of nutrition is unaffected. In fact, wherever the motor mechanism is muscular, as it is in all but the simplest animals, the necessary intervention of sensibility is an à priori axiom. Every action in the organs of such animals is a manifestation of muscular contractility, and there is no known means of exciting this contractility except by the stimulus of a nerve.

The heart is a muscle. Some years ago there was a school of physiologists advocating the hypothesis that the action of the heart was due to the irritability of its muscular tissue, which was stimulated by the presence of blood. The great Haller was the head of this school, and his "Memoires sur la nature sensible et irritable des parties" [Footnote 125] is still worthy the attention of experimentalists. And, indeed, when men saw the heart continue its pulsations some time after death, and even after removal from the body, and saw, moreover, that after pulsation had ceased it could be revived by the injection of warm blood, there seemed the strongest arguments in favor of the hypothesis. Unhappily for the hypothesis, the heart continues to beat long after all the blood has been pumped out of it, consequently its beating cannot be due to the stimulus of the blood.

In our own day the difficulty has to a considerable extent been removed by the discovery of a small nervous system specially allotted to the heart,—nerves and ganglia imbedded in its substance, which there do the work of nerves and ganglia everywhere else. Cut the heart into pieces, and each piece containing a ganglion will beat as before; the other pieces will be still. Beside this special cardiac system which influences the regular pulsations, there is the general nervous system, which accelerates and arrests these pulsations at every moment of our lives. The heart is thus connected with the general organism through the intervention of the great sensory apparatus. Filaments of what are called the pneumogastric nerves connect the heart with the spinal chord and cerebral masses; but it is not the influence of these filaments which causes the regular beatings of the heart (as physiologists formerly supposed), and the proof is that these filaments may all be cut, thus entirely isolating the heart from all connection with the great nervous centres, and yet the heart will continue tranquilly beating. What causes this? Obviously the stimulus comes from the heart's own nerves; and these are, presumably, excited by the molecular changes going on within it.

Physiologists, as we said just now, supposed that the filaments of the pneumogastric nerves distributed to the heart caused its beating. What then was their surprise, a few years since, when Weber announced that the stimulation of these fibres, instead of accelerating the heart's action, arrested it! Here was a paradox. All other muscles, it was said (but erroneously said), are excited to increased action when their nerves are stimulated, and here is a muscle which is paralyzed by the stimulation of its nerves. The fact was indisputable; an electric current passed through the pneumogastric did suddenly and invariably arrest the heart. Physiologists were interested. The frogs and rabbits of Europe had a bad time of it, called upon to answer categorically such questions put to their hearts. In a little while it appeared that although a strong electric current arrested the pulsations—and in mammals instantaneously—yet a feeble current accelerated instead of arresting them. The same opposite results followed a powerful and a gentle excitation of the upper region of the spinal chord.

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To these very important and suggestive facts, which throw a strong light on many phenomena hitherto obscure, let us add the interesting facts that in a healthy, vigorous animal, the heart quickly recovers its normal activity after the withdrawal of the electric stimulus; but in a sickly or highly sensitive animal the arrest is final.

Who does not read here the physiological explanation of the familiar fact that powerful mental shocks momently arrest the heart, and sometimes arrest it for ever? That which a powerful current will do applied to the pneumogastric nerve, will be done by a profound agitation of grief or joy—truly called a heart-shaking influence. The agitation of the great centres of thought is communicated to the spinal chord, and from it to the nerves which issue to various parts of the body: the limbs are violently moved, the glands are excited to increased activity, the tears flow, the facial muscles contract, the chest expands, laughter or sobs, dances of delight and shouts of joy, these and the manifold expressions of an agitated emotion, are the after results—the first effect is an arrest, more or less fugitive, followed by an increase of the heart's action. If the organism be vigorous, the effect of a powerful emotion is a sudden paleness, indicating a momentary arrest of the heart. This may be but for an instant; the heart pauses, and the lungs pause with it—"the breath is taken away." This is succeeded by an energetic palpitation; the lungs expand, the blood rushes to face and brain with increased force. Should the organism be sickly or highly sensitive, the arrest is of longer duration, and fainting, more or less prolonged, is the result. In a very sensitive or very sickly organism the arrest is final. The shock of joy and the shock of grief have both been known to kill.

The effects of a gentle stimulus we may expect to be very different, since we know that a feeble electric current stimulates the heart's action. The nature of the stimulus is always the same, no matter on what occasion it arises. It may arise from a dash of cold water on the face—as we see in the revival of the heart's action when we throw water on the face of a fainting person. It may arise from inhaling an irritant odor. It may arise from the pleasurable sight of a dear friend, or the thrill of delight at the new birth of an idea. In every case the brain is excited, either through an impression on a sensitive nerve, or through the impulses of thought; and the sensibility thus called into action necessarily discharges itself through one or more of the easiest channels; and among the easiest is that of the pneumogastric nerve. But the heart thus acted on in turn reacts. Its increased energy throws more blood into the brain, which draws its sustaining power from the blood.

Experimentalists have discovered another luminous fact connected with this influence of the brain upon the heart, namely, that although a current of a certain intensity (varying of course with the nature of the organism) will infallibly arrest the heart, if applied at once, yet if we begin with a feeble current and go on gradually increasing its intensity, we may at last surpass the degree which would have produced instantaneous arrest, and yet the heart will continue to beat energetically.

The effect of repetition in diminishing a stimulus is here very noticeable. It will serve to explain why, according to the traditions of familiar experience, we are careful to break the announcement of disastrous news, by intimating something much less calamitous, wherewith to produce the first shock, and then, when the heart has withstood that, we hope it may have energy to meet the more agitating emotions. The same fact will also serve, partly, to explain why from repetition the effect of smoking is no longer as it is at first to produce paleness, sweating, and sickness. The heart ceases to be sensibly affected by the stimulus.

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Returning to the effects of a gentle stimulus, we can read therein the rationale of change of scene, especially of foreign travel, in restoring the exhausted energies. The gentle excitement of novel and pleasurable sights is not, as people generally suppose, merely a mental stimulus—a pleasure which passes away without a physical influence; on the contrary, it is inseparably connected with an increased activity of the circulation, and this brings with it an increased activity of all the processes of waste and repair. If the excitement and fatigue be not too great, even the sickly traveller finds himself stronger and happier, in spite of bad food, irregular hours, and many other conditions which at home would have enfeebled him. I have heard a very distinguished physician (Sir Henry Holland) say that such is his conviction of the beneficial influence of even slight nervous stimulus on the nutritive processes, that when the patient cannot have change of scene, change of room is of some advantage—nay, even change of furniture, if there cannot be change of room!

To those who have thoroughly grasped the principle of the indissoluble conjunction of nutrition and sensation, such effects are obvious deductions. They point to the great importance of pleasure as an element of effective life. They lead to the question whether much of the superior health of youth is not due to the greater amount of pleasurable excitement which life affords to young minds.

Certain it is that much of the marvellous activity of some old men, especially of men engaged in politics or in interesting professions, may be assigned to the greater stimulus given to their bodily functions by the pleasurable excitement of their minds. Men who vegetate sink prematurely into old age. The fervid wheels of life revolve upon excitement. If the excitement be too intense, the wheels take fire; but if the mental stimulus be simply pleasurable, it is eminently beneficial.

Every impression reacts on the circulation, a slight impression producing a slight acceleration, a powerful impression, producing an arrest more or less prolonged. The "shock" of a wound and the "pain" of an operation cause faintness, sometimes death. Indeed, it is useful to know that many severe operations are dangerous only because of the shock or pain, and can be performed with impunity if the patient first be rendered insensible by chloroform. On the other hand, the mere irritation of a nerve so as to produce severe pain will produce syncope or death in an animal which is very feeble or exhausted. It is possible to crush the whole of the upper part of the spinal chord (the medulla oblongata) without arresting the action of the heart, if the animal has been rendered insensible by chloroform; whereas without such precautions a very slight irritation of the medulla suffices to arrest the heart.

A moment's reflection will disclose the reason of the remarkable differences observed in human beings in the matter of sensitiveness. The stupid are stupid, not simply because their nervous development is below the average, but also because the connection between the two great central organs, brain and heart, is comparatively languid; the pneumogastric is not in them a ready channel for the discharge of nervous excitement. The sensitive are sensitive because in them the connection is rapid and easy. All nervous excitement must discharge itself through one or more channels; but what channels, will depend on the native and acquired tendencies of the organism. In highly sensitive animals a mere prick on the skin can be proved to affect the beating of the heart; but you may lacerate a reptile without sensibly affecting its pulse. In like manner, a pleasurable sight or a suggestive thought will quicken the pulse of an intelligent man, whereas his stupid brother may be the spectator of festal or solemn scenes and the auditor of noble eloquence with scarcely a change.

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The highly sensitive organism is one in which the reactions of sensibility on the circulation, and of the circulation on the sensibility, are most direct and rapid. This is often the source of weakness and inefficiency—as we see in certain feminine natures of both sexes, wherein the excessive sensitiveness does not lie in an unusual development of the nervous centres, but in an unusual development of the direct connection between brain and heart. There are men and women of powerful brains in whom this rapid transmission of sensation to the heart is not observable; the nervous force discharges itself through other channels. There are men and women of small brains in whom "the irritability" is so great that almost every sensation transmits its agitating influence to the heart.

And now we are in a condition to appreciate the truth which was confusedly expressed in the ancient doctrine respecting the heart as the great emotional organ. It still lives in our ordinary speech, but has long been banished from the text-books of physiology, though it is not, in my opinion, a whit more unscientific than the modern doctrine respecting the brain (meaning the cerebral hemispheres) as the exclusive organ of sensation. That the heart, as a muscle, is not endowed with the property of sensibility—a property exclusively possessed by ganglionic tissue—we all admit. But the heart, as the central organ of the circulation, is so indissolubly connected with every manifestation of sensibility, and is so delicately susceptible to all emotional agitations, that we may not improperly regard it as the ancients regarded it, in the light of the chief centre of feeling; for the ancients had no conception of the heart as an organ specially endowed with sensibility—they only thought of it as the chief agent of the sensitive soul. And is not this the conception we moderns form of the brain? We do not imagine the cerebral mass, as a mere mass, and unrelated to the rest of the organism, to have in itself sensibility; but we conceive it as the centre of a great system, dependent for its activity on a thousand influences, sensitive because sensibility is the form of life peculiar to it, but living only in virtue of the vital activities of the whole organism. Thus the heart, because its action is momently involved in every emotion, and because every emotion reacts upon it, may, as truly as the brain, be called the great emotional centre. Neither brain nor heart can claim that title exclusively. They may claim it together.

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