PHYSICAL CONDITIONS OF MENTAL EXERTION.

"Laugh ye who boast your more mercurial powers,

That never feel a stupor, know no pause,

Nor need one; I am conscious, and confess,

Fearless, a soul that does not always think.”—Cowper.

THE confession of Cowper, would, I doubt not, be the confession of many others, if they were constrained to own the truth. It is certainly a very fortunate, and I doubt not a wise provision for such, that the operations of their minds are concealed, if they choose to conceal them, from all human observation, so that they can think or let it alone, just as they please, and nobody will ever know it.

There are those, I am aware, who entertain the opinion that the mind is ever active, knowing no respite and needing no pause; that at every moment of existence, even in sleep, it is still pursuing its onward progress, and maintaining an unbroken succession of ideas; that like the ceaseless flow of a river,

"lahitur,

Et labetur, in omne volubilis ævum."

It is not contended, indeed, that the mind is all this time conscious of its own operations, or, if conscious at the time, that it retains the recollection of this consciousness; but it is inferred from the immateriality of the mind, that it can never remain dormant. It is not my purpose, in this article, to investigate the truth of this opinion, which has been entertained both by the learned and by the unlearned. In the sense in which Cowper says he was conscious that he did not always think, few persons, I imagine, will be disposed to deny, that they too are conscious of the same fact. It may be safely presumed that most persons have at times experienced that degree of physical exhaustion, which incapacitated them for any well-directed and efficient mental effort. We do, indeed, sometimes meet with those whose "more mercurial powers" really seem to need no respite; from the rising of the sun until the going down of the same, and even until the noon of night, they keep the machinery of their minds in constant motion-driving its engine by the powerful energy of their own vito-galvanic battery. Nothing seems to stay the strong current of their thoughts, but their own determination.

That such persons should regard the mind as "something distinct from the body," and as independent of it in its opera tions, is not perhaps so remarkably strange. But to those who, by their daily experience, are compelled to admit the truthfulness of that declaration of the wise king of old, "much study is a weariness of the flesh," or to those whose waning health and exhausted physical energies incapacitate them for any considerable degree of mental effort, and which admonish them that

they have "need to make a pause," (perhaps a "solemn pause," to such, I say, the subject of this article-physical conditions of mental exertion-will not, as they peruse it, strike their minds as words of strange and doubtful import. To them, at least, the assertion that such is the connection of the human mind and body, that certain conditions of the latter are requisite to sustain the active energies of the former, will have all the force of a self-evident proposition. Their own conscious experience is to them all the proof that is requisite. Admitting, then, the proposition to be correct, it becomes a matter of some interest to know what these conditions are; for, just in so far as they are wanting, may we infer that deleterious or deranged action will ensue. Let us then inquire,

What are some of the physical conditions of mental exertion ?

1st. The organ of the mind must be perfectly formed in all its parts.

The brain is the great sensorium of the mind, by impressions upon which, the mind gains all its ideas of the existence, qualities, properties, and relations of external objects. These are the primary sources of all its cogitations; for how is it possible to think of that whose existence is not either obvious to our senses, or inferred from the existence of objects that are? The brain is, then, the medium of the mind's communication with the external world, and the organ of all its operations.

If, then, the organ of the mind be imperfectly formed, the medium of its communication with other objects, is, just in so far as this imperfection obtains, interrupted, and its capacity for receiving and retaining those impressions requisite to a correct knowledge of these things, is diminished or impaired. How can it be expected that the eye, for instance, should rightly perform its office, if it be in any considerable degree defective? If the focal distance of its lenses be either too long or too short, the light that is transmitted through them, will be either too diffused or too converged, and will fail to form a distinct image upon the retina. Thus objects will appear indistinct, confused, or distorted. So, likewise, if that portion of the brain, which is especially adapted to receive the final impression first made upon the retina, and by means of the optic nerve, transmitted to that part, be defective in structure or otherwise, we may justly infer that a correct impression will not be made.

There are some persons, who, owing to a defect, as I suppose, either in some organ of sense, or in the organization of some parts of the brain, or of the abnormal condition of those parts, cannot discriminate between particular qualities of color, sound, flavor, or odor, which are perfectly distinguishable to most other persons. I know an individual of unquestionable veracity, who

assured me that he could not distinguish the colors red and green; admitting, I presume, these colors to be of equal brilliancy. I directed his attention to the red and the green figures in the carpet before us; he said they appeared to him of the same color. The red rose and its green leaves must then, I suppose, present no pleasing contrast to his eye. I have heard of other similar instances.

If, then, any of the organs of sense, or those parts of the brain which receive and treasure up the impressions made primarily upon these organs, be defective, all that class of ideas which reach the mind through the medium of the defective faculty, must be imperfect; and hence all reflections upon these imperfect ideas, must also be of an indefinite character.

2d. The organ must be in a sound or healthy condition.

If a limb of the body, as the arm, be paralyzed, it cannot perform its office. If it be inflamed with rheumatism, every effort to use it will be painful, and its action will be inefficient. The arm may, nevertheless, be perfect in its formation. Every bone, joint, ligature, muscle, nerve, artery and vein, may be perfectly formed and properly adjusted.

And so it is with the brain. It may be complete as to its formation, but if it be diseased, wholly or in part, no just dependence can be placed upon its efficient action. It is a well known fact, that those diseases which affect the brain, do more or less affect the mind. It is also known that parts of the brain may be affected or injured, and a consequent degree of insane action, or want of action will be produced. Monomania is a disease too fully recognized at the present day, to admit of a doubt as to its reality.

As the brain is only a part of our corporeal system, nourished by the same circulating and assimilating process, and connected with every other part of it, even to the minutest fibre, by means of the spine and its innumerable ramifications, called nerves, which are of the same substance as the brain, it is reasonable to infer, and no one will dispute the correctness of the inference, that there should be a sympathy of the parts, and that when one member suffers, the others should also suffer with it. If one part receives an injury, the vitality of the other parts is directed to the injured part, to sustain the requisite healing process, and to effect the necessary repairs.

As all sensations are transmitted to the brain, by means of the nerves, if these sensations be uncommonly intense, the habitual current of the mind must be disturbed, or deranged, just in proportion to the degree of that intensity. The brain itself may become diseased in consequence, and its efficiency permanently impaired or destroyed. Intense physical suffering is well known to induce, in many cases, mental insanity. The

brain, then, and the corporeal system in general, must be in a healthy condition to insure correct and efficient mental action. 3d. The organ of the mind must be in a rested condition. When the laborer, fatigued with the toil of many hours, attempts to urge on the system to perform an unusual amount of labor, his wearied limbs seem reluctant to obey the high behests of the will, and in their own silent but significant language, declare their full conviction of the truth of that doctrine of ethics, that duty cannot exceed the limit of physical ability, and imploringly ask for

"Tired nature's sweet restorer, balmy sleep."

Who, that has exhausted the physical force derived from his daily food, does not know how toilsome are all subsequent efforts? Nature, indeed, has so constituted man, that in cases of emergency, he can, by the strong impulse of his will, push on the system to most extraordinary efforts; but he is sure to pay the penalty if he does. This usual draft upon his physical resources will inevitably result in a corresponding degree of subsequent languor, in painful sickness, or in sudden death. Such drafts are most unwise; nature forbids it, and gives the needful alarm; calls home her forces, and demands rest; and it is well if her admonitions be regarded. They are impolitic, for in case no serious injury be inflicted upon the system, the loss of time, requisite to make the necessary repairs, more than counterbalances, in ordinary cases, all the advantage which may have been secured. This capacity of the system was designed for times of pressing emergency, or of imminent peril, when, without it, great interests, or perhaps life itself, might be endangered.

It is thus with the mental faculties: a certain amount of mental labor may be performed without injury, nay, may conduce to the healthy condition of the brain, and to an increase of mental vigor; but beyond this, exhaustion, permanent debility, disease or death.

The capacity of different individuals for mental effort, is indeed widely different. Even in healthy organizations, there is great diversity, much more in unhealthy ones. There are those who are incapable of protracted mental effort, without consequent injury. There may be the appearance of health even when there is real debility; the cause is internal, and, to the unpractised eye, undiscoverable. There is little doubt that what is often stigmatized as laziness, is in many instances real exhaustion, arising from physical causes, involuntary and constitutional and for which, the individual thus afflicted is rather to be pitied than censured. The surest index, perhaps, by which one may detect in another this exhaustion, is the eye. Lack of lustre, as if the soul were wanting, a heavy movement or immo

bility of the eyeballs, a vacant stare, dilatation of the pupils, and drooping of the eyelids, are the sure indications of mental weariness, and the signals of nature demanding rest. To force the mind beyond this limit, is an act of violence that will work out its own vindication.

No fixed rule, in regard to the amount of mental labor which may be safely performed by any one, can be laid down. Every one may, however, after a little experience, decide for himself what his constitution will enable him to endure. He must not think of measuring his own capacity by that of others. He must not interpret the old adage-"what man has done, man can also do❞—to mean what any one man has done, every other man can do; for this would be to assume, that all are naturally endowed with equal capacity, which, evidently, is not the fact. If he cannot safely perform all he would, he must be content to do what he can. By a prudent exercise of his faculties, he may gradually increase their capability of action. Young students often commit great imprudences in this respect. In their ness to ascend the " hill of science," they tax their nervous system to the extreme limit of endurance, exhaust their energies, and, if they do not stumble and fall, they are, at least, compelled to halt, however impatient, and linger on the way long hours, perhaps weeks, months or years, in order to recruit. Like the crow in the fable, resolved to do great things, exceeding their ability, they only get entangled in the fleece of their intended prey, and get their wings clipped for their rash folly.

eager

4th. The organ of the mind must, by excitation, be put in a susceptible condition. During the hours of "soft repose," every slumbering faculty ceases to preform its wonted office. The eye is closed to all external objects, the ear hears not, it may be, the tread of the midnight robber, the nerves are unconscious of touch, these outer sentinels are all inactive; no intelligence from the external world penetrates the now silent abode of the soul. Reflection ceases, and with it all consciousness. Only those motions of the system requisite to sustain life, such as the pulsations of the heart, circulation of the blood, and respiration, continue; but the mind knows it not. Where is it? Has it gone on a voyage of discovery to the spirit land, and left the body to its repose ?—or is it too, that ethereal essence that animates, actuates and controls the body, fast asleep? It sees not, hears not, knows not that aught else exists, or that even itself exists. Ah! but its faculties are all suspended, its organs are all dormant. The delicate machinery of thought has ceased its rapid motion; and the manufacture of its exquisitely fine and impalpable tissue, has for the time been entirely suspended. Why is this? If the body be weary, let it repose; but must the immortal mind too be chained down in oblivion and silence,