# The Conservation of Energy/Appendix 2

CORRELATION OF NERVOUS AND MENTAL FORCES.
By ALEXANDER BAIN, LL. D.,
PROFESSOR OF LOGIC AND MENTAL PHILOSOPHY IN THE UNIVERSITY OF ABERDEEN.
THE CORRELATION OF NERVOUS AND MENTAL FORCES.
The doctrine called the correlation, persistence, equivalence, transmutability, indestructibility of force, or the conservation of energy, is a generality of such compass that no single form of words seems capable of fully expressing it; and different persons may prefer different statements of it. My understanding of the doctrine is, that there are five chief powers or forces in Nature: one mechanical or molar, the momentum of moving matter; the others molecular, or embodied in the molecules, also supposed in motion—these are, heat, light, chemical force, electricity. To these powers, which are unquestionable and distinct, it is usual to add vital force, of which, however, it is difficult to speak as a whole; but one member of our vital energies, the nerve-force, allied to electricity, fully deserves to rank in the correlation.
Taking the one mechanical force, and those three of ​the molecular named heat, chemical force, electricity, there has now been established a definite rate of commutation, or exchange, when any one passes into any other. The mechanical equivalent of heat, the 772 foot-pounds of Joule, expresses the rate of exchange between mechanical momentum and heat: the equivalent or exchange of heat and chemical force is given (through the researches of Andrews and others) in the figures expressing the heat of combinations; for example, one pound of carbon burnt evolves heat enough to raise 8,080 pounds of water one degree, C. The combination of these to equivalents would show that the consumption of half a pound of carbon would raise a man of average weight to the highest summit of the Himalayas.
It is an essential part of the doctrine, that force is never absolutely created, and never absolutely destroyed, but merely transmuted in form or manifestation.
As applied to living bodies, the following are the usual positions. In the growth of plants, the forces of the solar ray—heat and light—are expended in decomposing (or deoxidizing) carbonic acid and water, and in building up the living tissues from the liberated carbon and the other elements; all which force is given up when these tissues are consumed, either as fuel in ordinary combustion, or as food in animal combustion.
It is this animal combustion of the matter of plants, and of animals (fed on plants)—namely, the reoxida​tion of carbon, hydrogen, etc.—that yields all the manifestations of power in the animal frame. And, in particular, it maintains (1) a certain warmth or temperature of the whole mass, against the cooling power of surrounding space; it maintains (2) mechanical energy, as muscular power; and it maintains (3) nervous power, or a certain flow of the influence circulating through the nerves, which circulation of influence, besides reacting on the other animal processes—muscular, glandular, etc. —has for its distinguishing concomitant the mind.
The extension of the correlation of force to mind, if at all competent, must be made through the nerve-force, a genuine member of the correlated group. Very serious difficulties beset the proposal, but they are not insuperable.
The history of the doctrines relating to mind, as connected with body, is in the highest degree curious and instructive, but, for the purpose of the present paper, we shall notice only certain leading stages of the speculation.
Not the least important position is the Aristotelian; a position in some respects sounder than what followed and grew out of it. In Aristotle, we have a kind of gradation from the life of plants to the highest form of ​human intelligence. In the following diagram, the continuous lines may represent the material substance, and the dotted lines the immaterial:
A. Soul of Plants.
B. Animal Soul.
C. Human Soul—Nous—Intellect.
. . . . . . . . Body and mind inseparable. II. Active intellect—cognition of the highest principles.
. . . . . . . . Pure form; detached from matter; the prime mover of all; immortal.
All the phases of life and mind are inseparably interwoven with the body (which inseparability is Aristotle's definition of the soul) except the last, the active nous, or intellect, which is detached from corporeal matter, self-subsisting, the essence of Deity, and an immortal substance, although the immortality is not personal to the individual. (The immateriality of this higher intellectual agent was net, however, that thorough-going: negation of all material attributes which we now understand by the word "immaterial.") How such a self-subsisting and purely spiritual soul could hold communication with the body-leagued souls, Aristotle was at a loss to say—the difficulty reappeared after him, and ​has never been got over. That there should be an agency totally apart from, and entirely transcending, any known powers of inert matter, involves no difficulty—for who is to limit the possibilities of existence? The perplexity arises only when this radically new and superior principle is made to be, as it were, off and on with the material principle; performing some of its functions in pure isolation, and others of an analogous kind by the aid of the lower principle. The difference between the active and the passive reason of Aristotle is a mere difference of gradation; the supporting agencies assumed by him area total contrast in kind —wide as the poles asunder. There is no breach of continuity in the phenomena, there is an impassable chasm between their respective foundations.
Fifteen centuries after Aristotle, we reach what may be called the modern settlement of the relations of mind and body, effected by Thomas Aquinas. He extended the domain of the independent immaterial principle from the highest intellectual soul of Aristotle to all the three souls recognized by him—the vegetable or plant soul (without consciousness), the animal soul (with consciousness), and the intellect throughout. The two lower souls—the vegetable and the animal—need the coöperation of the body in this life; the intellect works without any bodily organ, except that it makes use of the perceptions of the senses.
A. Vegetable or Nutritive Soul.
B. Animal Soul.
C. Intellect.
The animal soul, B, contains sensation, appetite, and emotion, and is a mixed or two-sided entity; but the intellect, C, is a purely one-sided entity, the immaterial. This does not relieve our perplexities; the phenomena are still generically allied and continuous—sensation passes into intellect without any breach of continuity; but as regards the agencies, the transition from a mixed or united material and immaterial substance to an immaterial substance apart, is a transition to a differently constituted world, to a transcendental sphere of existence.
The settlement of Aquinas governed all the schools and all the religious creeds, until quite recent times; it is, for example, substantially the view of Bishop Butler. At the instance of modern physiology, however, it has undergone modifications. The dependence of purely intellectual operations, as memory, upon the material processes, has been reluctantly admitted by the partisans of an immaterial principle; an admission incompatible with the isolation of the intellect in Aristotle and in Aquinas. This more thorough-going connection of the ​mental and the physical has led to a new form of expressing the relationship, which is nearer the truth, without being, in my judgment, quite accurate. It is now often said the mind and the body act upon each other; that neither is allowed, so to speak, to pursue its course alone—there is a constant interference, a mutual influence between the two. This view is liable to the following objections:
1. In the first place, it assumes that we are entitled to speak of mind apart from body, and to affirm its powers and properties in that separate capacity. But of mind apart from body we have no direct experience, and absolutely no knowledge. The wind may act upon the sea, and the waves may react upon the wind; but the agents are known in separation—they are seen to exist apart before the shock of collision; but we are not permitted to see a mind acting apart from its material companion.
2. In the second place, we have every reason for believing that there is an unbroken material succession, side by side with all our mental processes. From the ingress of a sensation, to the outgoing responses in action, the mental succession is not for an instant dissevered from a physical succession. A new prospect bursts upon the view; there is a mental result of sensations, emotion, thought, terminating in outward displays of speech or gesture. Parallel to this mental ​series is the physical series of facts, the successive agitation of the physical organs, called the eye, the retina, the optic nerve, optic centres, cerebral hemispheres, outgoing nerves, muscles, etc. There is an unbroken physical circle of effects, maintained while we go the round of the mental circle of sensation, emotion, and thought. It would be incompatible with every thing we know of the cerebral action to suppose that the physical chain ends abruptly in a physical void, occupied by an immaterial substance; which immaterial substance, after working alone, imparts its results to the other edge of the physical break, and determines the active response—two shores of the material with an intervening ocean of the immaterial. There is, in fact, no rupture of nervous continuity. The only tenable supposition is, that mental and physical proceed together, as individual twins. When, therefore, we speak of a mental cause, a mental agency, we have always a two-sided cause; the effect produced is not the effect of mind alone, but of mind in company with body. That mind should have operated on the body, is as much as to say that a two-sided phenomenon, one side being bodily, can influence the body; it is, after all, body acting upon body. When a shock of fear paralyzes digestion, it is not the emotion of fear, in the abstract, or as a pure mental existence, that does the harm; it is the emotion in company with a peculiarly excited condition of the brain and nervous system; and ​it is this condition of the brain that deranges the stomach. When physical nourishment, or physical stimulant, acting through the blood, quiets the mental irritation, and restores a cheerful tone, it is not a bodily fact causing a mental fact by a direct line of causation: the nourishment and the stimulus determine the circulation of blood to the brain, give a new direction to the nerve-currents, and the mental condition corresponding to this particular mode of cerebral action henceforth manifests itself. The line of mental sequence is thus, not mind causing body, and body causing mind, but mind-body giving birth to mind-body; a much more intelligible position. For this double or conjoint causation, we can produce evidence; for the single-handed causation we have no evidence.
If it were not my peculiar province to endeavor to clear up the specially metaphysical difficulties of the relationship of mind and body, I would pass over what is to me the most puzzling circumstance of the relationship, and indeed the only real difficulty in the question.
I say the real difficulty, for factitious difficulties in abundance have been made out of the subject. It is made a mystery how mental functions and bodily functions should be allied together at all. That, however, is no business of ours; we accept this alliance, as we do any other alliance, such as gravity with inert matter, or light with heat. As a fact of the universe, the union ​is, properly speaking, just as acceptable, and as intelligible, as the separation would be, if that were the fact. The real difficulty is quite another thing.
What I have in view is this: when I speak of mind as allied with body—with a brain and its nerve-currents—I can scarcely avoid localizing the mind, giving it a local habitation. I am thereupon asked to explain what always puzzled the schoolmen, namely, whether the mind is all in every part, or only all in the whole; whether in tapping any point I may come at consciousness, or whether the whole mechanism is wanted for the smallest portion of consciousness. One might perhaps turn the question by the analogy of the telegraph wire, or the electric circuit, and say that a complete circle of action is necessary to any mental manifestation; which is probably true. But this does not meet the case. The fact is that, all this time we are speaking of nerves and wires, we are not speaking of mind, properly so called, at all; we are putting forward physical facts that go along with it, but these physical facts are not the mental fact, and they even preclude us from thinking of the mental fact. We are in this fix: mental states and bodily states are utterly contrasted; they cannot be compared, they have nothing in common except the most general of all attributes, degree, and order in time; when engaged with one we must be oblivious of all that distinguishes the other. When I am study ​ing a brain and nerve communicating, I am engrossed with properties exclusively belonging to the object or material world; I am at that moment (except by very rapid transitions or alternations) unable to conceive a truly mental fact, my truly mental consciousness. Our mental experience, our feelings and thoughts, have no extension, no place, no form or outline, no mechanical division of parts; and we are incapable of attending to any thing mental until we shut off the view of all that. Walking in the country in spring, our mind is occupied with the foliage, the bloom, and the grassy meads, all purely objective things; we are suddenly and strongly arrested by the odor of the May-blossom; we give way for a moment to the sensation of sweetness: for that moment the objective regards cease; we think of nothing extended; we are in a state where extension has no footing; there is, to us, place no longer. Such states are of short duration, mere fits, glimpses; they are constantly shifted and alternated with object states, but while they last and have their full power we are in a different world; the material world is blotted out, eclipsed, for the instant unthinkable. These subject-moments are studied to advantage in bursts of intense pleasure, or intense pain, in fits of engrossed reflection, especially reflection upon mental facts; but they are seldom sustained in purity beyond a very short interval; we are constantly returning to the object-side of things— ​To the world where extension and place have their being.
This, then, as it appears to me, is the only real difficulty of the physical and mental relationship. There is an alliance with matter, with the object, or extended world; but the thing allied, the mind proper, has itself no extension, and cannot be joined in local union. Now, we have no form of language, no familiar analogy, suited to this unique conjunction; in comparison with all ordinary unions, it is a paradox or a contradiction. We understand union in the sense of local connection; here is a union where local connection is irrelevant, unsuitable, contradictory, for we cannot think of mind without putting ourselves out of the world of place. When, as in pure feeling—pleasure or pain—we change to the subject attitude from the object attitude, we have undergone a change not to be expressed by place; the fact is not properly described by the transition from the external to the internal, for that is still a change in the region of the extended. The only adequate expression is a change of state: a change from the state of the extended cognition to a state of unextended cognition. By various theologians, heaven has been spoken of us not a place, but a state; and this is the only phrase that I can find suitable to describe the vast, though familiar and easy, transition from the material or extended, to the immaterial or unextended side of the universe of being. ​When, therefore, we talk of incorporating mind with brain, we must be held as speaking under an important reserve or qualification. Asserting the union in the strongest manner, we must yet deprive it of the almost invincible association of union in place. An extended organism is the condition of our passing into a state where there is no extension. A human being is an extended and material thing, attached to which is the power of becoming alive to feeling and thought, the extreme remove from all that is material; a condition of trance wherein, while it lasts, the material drops out of view—so much so, that we have not the power to represent the two extremes as lying side by side, as container and contained, or in any other mode of local conjunction. The condition of our existing thoroughly in the one, is the momentary eclipse or extinction of the other.
The only mode of union that is not contradictory is the union of close succession in time; or of position in a continued thread of conscious life. We are entitled to say that the same being is, by alternate fits, object and subject, under extended and under unextended consciousness; and that without the extended consciousness the unextended would not arise. Without certain peculiar modes of the extended—what we call a cerebral organization, and so on—we could not have those times of trance, our pleasures, our pains, and our ideas, which ​at present we undergo fitfully and alternately with our extended consciousness.
Having thus called attention to the metaphysical difficulty of assigning the relative position of mind and matter, I will now state briefly what I think the mode of dealing with mind in correlation with the other forces. That there is a definite equivalence between mental manifestations and physical forces, the same as between the physical forces themselves, is, I think, conformable to all the facts, although liable to peculiar difficulties in the way of decisive proof:
I. The mental manifestations are in exact proportion to their physical supports.
If the doctrine of the thorough-going connection of mind and body is good for any thing, it must go this length. There must be a numerically-proportioned rise and fall of the two together. I believe that all the unequivocal facts bear out this proportion.
Take first the more obvious illustrations. In the employment of external agents, as warmth and food, all will admit that the sensation rises exactly as the stimulant rises, until a certain point is reached, when the agency changes its character; too great heat destroying the tissues, and too much food impeding digestion. There is, although we may not have the power to fix it, a sensational equivalent of heat, of food, of exercise, of sound, of light; there is a definite change of feeling, an ​accession of pleasure or of pain, corresponding to a rise of temperature in the air of 10°, 20°, or 30°. And so with regard to every other agent operating upon the human sensibility: there is, in each set of circumstances, a sensational equivalent of alcohol, of odors, of music, of spectacle.
It is this definite relation between outward agents and the human feelings that renders it possible to discuss human interests from the objective side, the only accessible side. We cannot read the feelings of our fellows; we merely presume that like agents will affect them all in nearly the same way. It is thus that we measure men's fortunes and felicity by the numerical amount of certain agents, as money, and by the absence or low degree of certain other agents, the causes of pain and the depressors of vitality. And, although the estimate is somewhat rough, this is not owing to the indefiniteness of the sensational equivalent, but to the complications of the human system, and chiefly to the narrowness of the line that everywhere divides the wholesome from the unwholesome degrees of all stimulants.
Let us next represent the equivalence under vital or physiological action. The chief organ concerned is the brain; of which we know that it is a system of myriads of connecting threads, ramifying, uniting, and crossing at innumerable points; that these threads are actuated or made alive with a current influence called the nerve ​force; that this nerve-force is a member of the group of correlating forces; that it is immediately derived from the changes in the blood, and in the last resort from oxidation, or combustion, of the materials of the food, of which combustion it is a definite equivalent. We know, further, that there can be no feeling, no volition, no intellect, without a proper supply of blood, containing both oxygen and the material to be oxidized; that, as the blood is richer in quality in regard to these constituents, and more abundant in quantity, the mental processes are more intense, more vivid. We know also that there are means of increasing the circulation in one organ, and drawing it off from another, chiefly by calling the one into greater exercise, as when we exert the muscles or convey food to the stomach; and that, when mental processes are more than usually intensified, the blood is proportionally drawn to the brain; the oxidizing process is there in excess, with corresponding defect and detriment in other organs. In high mental excitement, digestion is stopped; muscular vigor is abated except in the one form of giving vent to the feelings, thoughts, and purposes; the general nutrition languishes; and, if the state were long continued or oft repeated, the physical powers, strictly so called, would rapidly deteriorate. We know, on the other extreme, that sleep is accompanied by reduced circulation in the brain; there is in fact a reduced circulation generally; ​while of that reduced amount more goes to the nutritive functions than to the cerebral.
In listening to Dr. Frankland's lecture on "Muscular Power," delivered at the Royal Institution of London, I noticed that, in accounting for the various items of expenditure of the food, he gave "mental work" as one heading, but declined to make an entry thereinunder. I can imagine two reasons for this reserve, the statement of which will further illustrate the general position. In the first place, it might be supposed that mind is a phenomenon so anomalous, uncertain, so remote from the chain of material cause and effect, that it is not even to be mentioned in that connection.
To which I should say, that mind is indeed, as a phenomenon, widely different from the physical forces, but, nevertheless, rises and falls in strict numerical concomitance with these: so that it still enters, if not directly, at least indirectly, into the circle of the correlated forces. Or, secondly, the lecturer may have held that, though a definite amount of the mental manifestations accompanies a definite amount of oxidation in the special organs of mind, there is no means of reducing this to a measure, even in an approximate way. To this I answer, that the thing is difficult but not entirely impracticable. There is a possibility of giving, approximately at least, the amount of blood circulating in the brain, in the ordinary waking state; and, as during a ​period of intense excitement we know that there is a general reduction, almost to paralysis, of the collective vital functions, we could not be far mistaken in saying that, in that case, perhaps one-half or one-third of all the oxidation of the body was expended in keeping up the cerebral fires.
It is a very serious drawback in any department of knowledge, where there are relations of quantity, to be unable to reduce them to numerical precision. This is the case with mind in a great degree, although not with it alone; many physical qualities are in the same state of unprecise measurement. We cannot reduce to numbers the statement of a man's constitutional vigor, so as to say how much he has lost by fatigue, by disease, by age, or how much he has gained by a certain healthy regimen. Undoubtedly, however, it is in mind that the difficulties of attaining the numerical statement are greatest if not nearly insuperable. When we say that one man is more courageous, more loving, more irascible than another, we apply a scale of degree, existing in our own mind, but so vague that we may apply it differently at different times, while we can hardly communicate it to others exactly as it stands to ourselves. The consequence is, that a great margin of allowance must always be made in those statements; we can never run a close argument, or contend for a nice shade of distinction. Between the extremes of timidity ​and courage of character the best observer could not entertain above seven or eight varieties of gradation, while two different persons consulting together could hardly agree upon so minute a subdivision as that. The phrenologists, in their scale of qualities, had the advantage of an external indication of size, but they must have felt the uselessness of graduating this beyond the delicacy of discriminating the subjective side of character; and their extreme scale included twenty steps or interpolations.
Making allowance for this inevitable defect, I will endeavor to present a series of illustrations of the principle of correlation as applied to mind, in the manner explained. I deal not with mind directly, but with its material side, with whose activity, measured exactly as we measure the other physical forces, true mental activity has a definite correspondence.
Let us suppose, then, a human being with average physical constitution, in respect of nutritive vigor, and fairly supplied with food and with air, or oxygen. The result of the oxidation of the food is a definite total of force, which may be variously distributed. The demand made by the brain, to sustain the purely mental functions, may be below average, or above average; there will be a corresponding, but inverse, variation of the remainder available for the more strictly physical pro​cesses, as muscular power, digestive power, animal heat, and so on.
In the first case supposed, the case of a small demand for mental work and excitement, we look for, and we find, a better physique—greater muscular power and endurance, more vigor of digestion, rendering a coarser food sufficient for nourishment, more resistance to excesses of cold and heat; in short, a constitution adapted to physical drudgery and physical hardship.
Take, now, the other extreme. Let there be a great demand for mental work. The oxidation must now be disproportionately expended in the brain; less is given to the muscles, the stomach, the lungs, the skin, and secreting organs generally. There is a reduction of the possible muscular work, and of the ability to subsist on coarser food, and to endure hardship. Experience confirms this inference; the common observation of mankind has recognized the fact—although in a vague, unsteady form—that the head-worker is not equally fitted to be a hand-worker. The master, mistress, or overseer has each more delicacy of sense, more management, more resource, than the manual operatives, but to these belongs the superiority of muscular power and persistence.
There is nothing incompatible with the principle in allowing the possibility of combining, under certain favorable conditions, both physical and mental exertion ​in considerable amount. In fact, the principle teaches us exactly how the thing may be done. Improve the quality and increase the quantity of the food; increase the supply of oxygen by healthy residence; let the habitual muscular exertion be such as to strengthen and not impair the functions; abate as much as possible all excesses and irregularities, bodily and mental; add the enormous economy of an educated disposal of the forces; and you will develop a higher being, a greater aggregate of power. You will then have more to spare for all kinds of expenditure—for the physico-mental, as well as for the strictly physical. What other explanation is needed of the military superiority of the officer over the common soldier? of the general efficiency of the man nourished, but not enervated, by worldly abundance?
It may be possible, at some future stage of scientific inquiry, to compute the comparative amount of oxidation in the brain during severe mental labor. Even now, from obvious facts, we must pronounce it to be a very considerable fraction of the entire work done in the system. The privation of the other interests during mental exertion is so apparent, so extensive, that if the exertion should happen to be long continued, a liberal atonement has to be made in order to stave off general insolvency. Mental excess counts as largely as muscular excess in the diversion of power; it would be com​petent to suppose either the one or the other reducing the remaining forces of the system to one-half of their proper amount. In both cases, the work of restoration must be on the same simple plan of redressing the inequality, of allowing more than the average flow of blood to the impoverished organs, for a length of time corresponding to the period when their nourishment has been too small. It is in this consideration that we seem to have the reasonable, I may say the arithmetical, basis of the constitutional treatment of chronic disease. We repay the debt to Nature by allowing the weakened organ to be better nourished and less taxed, according to the degradation it has undergone by the opposite line of treatment. In a large class of diseases we have obviously a species of insolvency, to be dealt with according to the sound method of readjusting the relations of expenditure and income. And, if such be the true theory, it seems to follow that medication is only an inferior adjunct. Drugs, even in their happiest application, can but guide and favor the restorative process; just as the stirring of a fire may make it burn, provided there be the needful fuel.
There is thus a definite, although not numerically-statable relation, between the total of the physico-mental forces and the total of the purely physical processes. The grand aggregate of the oxidation of the system includes both; and, the more the force taken up by one, ​the less is left to the other. Such is the statement of the correlation of mind to the other forces of Nature. We do not deal with pure mind—mind in the abstract; we have no experience of an entity of that description. We deal with a compound or two-sided phenomenon—mental on one side, physical on the other; there is a definite correspondence in degree, although a difference of nature, between the two sides; and the physical side is itself in full correlation with the recognized physical forces of the world.
II. There remains another application of the doctrine, perhaps equally interesting to contemplate, and more within my special line of study. I mean the correlation of the mental forces among themselves (still viewed in the conjoint arrangement). Just as we assign limits to mind as a whole, by a reference to the grant of physical expenditure, in oxidation, etc., for the department, so we must assign limits to the different phases or modes of mental work—thought, feeling, and so on—according to the share allotted to each; so that, while the mind as a whole may be stinted by the demands of the non-mental functions, each separate manifestation is bounded by the requirements of the others. This is an inevitable consequence of the general principle, and equally receives the confirmation of experience. There is the same absence of numerical precision of estimate; our scale of quantity can have but few divisions ​between the highest and the lowest degrees, and these not well fixed.
What is required for this application of the principle is, to ascertain the comparative cost, in the physical point of view, of the different functions of the mind.
The great divisions of the mind are—feeling, will, and thought; feeling, seen in our pleasures and pains; will, in our labors to attain the one and avoid the other; thought, in our sensations, ideas, recollections, reasonings, imaginings, and so on. Now, the forces of the mind, with their physical supports, may be evenly or unevenly distributed over the three functions. They may go by preference either to feeling, to action, or to thinking; and, if more is given to one, less must remain to the others, the entire quantity being limited.
First, as to the feelings. Every throb of pleasure costs something to the physical system; and two throbs cost twice as much as one. If we cannot fix a precise equivalent, it is not because the relation is not definite, but from the difficulties of reducing degrees of pleasure to a recognized standard. Of this, however, there can be no reasonable doubt—namely, that a large amount of pleasure supposes a corresponding large expenditure of blood and nerve-tissue, to the stinting, perhaps, of the active energies and the intellectual processes. It is a matter of practical moment to ascertain what pleasures cost least, for there are thrifty and unthrifty modes of ​spending our brain and heart's blood. Experience probably justifies us in saying that the narcotic stimulants are, in general, a more extravagant expenditure than the stimulation of food, society, and fine art. One of the safest of delights, if not very acute, is the delight of abounding physical vigor; for, from the very supposition, the supply to the brain is not such as to interfere with the general interests of the system. But the theory of pleasure is incomplete without the theory of pain.
As a rule, pain is a more costly experience than pleasure, although sometimes economical as a check to the spendthrift pleasures. Pain is physically accompanied by an excess of blood in the brain, from at least two causes—extreme intensity of nervous action, and conflicting currents, both being sources of waste. The sleeplessness of the pained condition means that the circulation is never allowed to subside from the brain; the irritation maintains energetic currents, which bring the blood copiously to the parts affected.
There is a possibility of excitement, of considerable amount, without either pleasure or pain; the cost here is simply as the excitement: mere surprises may be of this nature. Such excitement has no value, except intellectually; it may detain the thoughts, and impress the memory, but it is not a final end of our being, as pleasure is; and it does not waste power to the extent ​that pain does. The ideally best condition is a moderate surplus of pleasure—a gentle glow, not rising into brilliancy or intensity, except at considerable intervals (say a small portion of every day), falling down frequently to indifference, but seldom sinking into pain.
Attendant on strong feeling, especially in constitutions young or robust, there is usually a great amount of mere bodily vehemence, as gesticulation, play of countenance, of voice, and so on. This counts as muscular work, and is an addition to the brain-work. Properly speaking, the cerebral currents discharge themselves in movements, and are modified according to the scope given to those movements. Resistance to the movements is liable to increase the conscious activity of the brain, although a continuing resistance may suppress the entire wave.
Next as to the will, or our voluntary labors and pursuits for the great ends of obtaining pleasure and warding off pain. This part of our system is a compound experience of feeling and movement; the properly mental fact being included under feeling—that is, pleasure and pain, present or imagined. When our voluntary endeavors are successful, a distinct throb of pleasure is the result, which counts among our valuable enjoyments: when they fail, a painful and depressing state ensues. The more complicated operations of the will, as in adjusting many opposite interests, bring in ​the element of conflict, which is always painful and wasting. Two strong stimulants pointing opposite ways, as when a miser has to pay a high fee to the surgeon that saves his eyesight, occasion a fierce struggle and severe draft upon the physical supports of the feelings.
Although the processes of feeling all involve a manifest, and it may be a serious, expenditure of physical power, which of course is lost to the purely physical functions; and although the extreme degrees of pleasure, of pain, or of neutral excitement, must be adverse to the general vigor; yet the presumption is, that we can afford a certain moderate share of all these without too great inroads on the other interests. It is the thinking or intellectual part of us that involves the heaviest item of expenditure in the physico-mental department. Any thing like a great or general cultivation of the powers of thought, or any occupation that severely and continuously brings them into play, will induce such a preponderance of cerebral activity, in oxidation and in nerve-currents, as to disturb the balance of life, and to require special arrangements for redeeming that disturbance. This is fully verified by all we know of the tendency of intellectual application to exhaust the physical powers, and to bring on early decay.
A careful analysis of the operations of the intellect enables us to distinguish the kind of exercises that in​involve the greatest expenditure, from the extent and the intensity of the cerebral occupation. I can but make a rapid selection of leading points:
First. The mere exercise of the senses, in the way of attention, with a view to watch, to discriminate, to identify, belongs to the intellectual function, and exhausts the powers according as it is long continued, and according to the delicacy of the operation; the meaning of delicacy being that an exaggerated activity of the organ is needed to make the required discernment. To be all day on the qui vive for some very slight and barely perceptible indications to the eye or the ear, as in catching an indistinct speaker, is an exhausting labor of attention.
Secondly. The work of acquisition is necessarily a process of great nervous expenditure. Unintentional imitation costs least, because there is no forcing of reluctant attention. But a course of extensive and various acquisitions cannot be maintained without a large supply of blood to cement all the multifarious connections of the nerve-fibres, constituting the physical side of acquisition. An abated support of other mental functions, as well as of the purely physical functions, must accompany a life devoted to mental improvement, whether arts, languages, sciences, moral restraints, or other culture.
Of special acquisitions, languages are the most ​apparently; voluminous; but the memory for visible or pictorial aspects, if very high, as in the painter and the picturesque poet, makes a prodigious demand upon the plastic combinations of the brain.
The acquisition of science is severe, rather than multifarious; it glories in comprehending much in little, but that little is made up of painful abstract elements, every one of which, in the last resort, must have at its beck a host of explanatory particulars: so that, after all, the burden lies in the multitude. If science is easy to a select number of minds, it is because there is a large spontaneous determination of force to the cerebral elements that support it; which force is supplied by the limited common fund, and leaves so much the less for other uses.
If we advert to the moral acquisitions and habits in a well-regulated mind, we must admit the need of a large expenditure to build up the fabric. The carefully-poised estimate of good and evil for self, the ever-present sense of the interests of others, and the ready obedience to all the special ordinances that make up the morality of the time, however truly expressed in terms of high and abstract spirituality, have their counterpart in the physical organism; they have used up a large and definite amount of nutriment, and, had they been less developed, there would have been a gain of power to some other department, mental or physical.
​Refraining from further detail on this head, I close the illustration by a brief reference to one other aspect of mental expenditure, namely, the department of intellectual production, execution, or creativeness, to which in the end our acquired powers are ministerial. Of course, the greater the mere continuance or amount of intellectual labor in business, speculation, fine art, or any thing else, the greater the demand on the physique. But amount is not all. There are notorious differences of severity or laboriousness, which, when closely examined, are summed up in one comprehensive statement—namely, the number, the variety, and the conflicting nature of the conditions that have to be fulfilled. By this we explain the difficulty of work, the toil of invention, the harassment of adaptation, the worry of leadership, the responsibility of high office, the severity of a lofty ideal, the distraction of numerous sympathies, the meritoriousness of sound judgment, the arduousness of any great virtue. The physical facts underlying the mental fact are a wide-spread agitation of the cerebral currents, a tumultuous conflict, a consumption of energy.
It is this compliance with numerous and opposing conditions that obtains the most scanty justice in our appreciation of character. The unknown amount of painful suppression that a cautious thinker, a careful writer, or an artist of fine taste, has gone through, represents a great physico-mental expenditure. The ​regard to evidence is a heavy drag on the wings of speculative daring. The greater the number of interests that a political schemer can throw overboard, the easier his work of construction. The absence of restraints—of severe conditions—in fine art, allows a flush and ebullience, an opulence of production, that is often called the highest genius. The Shakespearean profusion of images would have been reduced to one-half, if not less, by the self-imposed restraints of Pope, Gray, or Tennyson. So, reckless assertion is fuel to eloquence. A man of ordinary fairness of mind would be no match for the wit and epigram of Swift.
And again. The incompatibility of diverse attributes, even in minds of the largest compass (which supposes equally large physical resources), belongs to the same fundamental law. A great mind may be great in many things, because the same kind of power may have numerous applications. The scientific mind of a high order, is also the practical mind; it is the essence of reason in every mode of its manifestation—the true philosopher in conduct as well as in knowledge. On such a mind also, a certain amount of artistic culture may be superinduced; its powers of acquisition may be extended so far. But the spontaneous, exuberant, imaginative flow, the artistic nature at the core, never was, cannot be, included in the same individual. Aristotle could not be also a tragic poet; nor Newton a third-rate ​portrait-painter. The cost of one of the two modes of intellectual greatness is all that can be borne by the most largely-endowed personality; any appearances to the contrary are hollow and delusive.
Other instances could be given. Great activity and great sensibility are extreme phases, each using a large amount of power, and therefore scarcely to be coupled in the same system. The active, energetic man, loving activity for its own sake, moving in every direction, wants the delicate circumspection of another man who does not love activity for its own sake, but is energetic only at the spur of his special ends.
And once more. Great intellect as a whole is not readily united with a large emotional nature. The incompatibility is best seen by inquiring whether men of overflowing sociability are deep and original thinkers, great discoverers, accurate inquirers, great organizers in affairs; or whether their greatness is not limited to the spheres where feeling performs a part—poetry, eloquence, and social ascendency.