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The office of the nerves is to receive and transmit impressions to and from the brain ; so that an impression made upon the extremity of a nerve may reach the brain, and an impression upon the brain may reach any part of the body through the medium of the nerves.
Here then we are able to discover some of the links of the sympathetic chain, which connects the body and the mind. An unusual condition of any part of the body, affecting the nerves of that part, propagates a peculiar influence to the brain ;-the state of the brain being thus affected, may modify the operations of the mind. On the other hand, the acts and emotions of the mind may affect the condition of the brain, and in this way modify the influence, which this organ transmits to the various parts of the body; thus drawing one or more of these parts into sympathy with the mind. But this point will be made clearer by a brief examination of sensation and voluntary motion.
In the function of sensation an impression is made upon the extremity of a nerve ; this impression is transmitted along the nerve to the brain, where it is taken cognizance of by the mind. Thus there are three steps in the process of sensation, viz., the change in the extremity of the nerve—the propagation of this effect along the nerve to the brain—the change in the brain, which is appreciated by the mind. We shall not go into the arguments, which demonstrate the existence of these three steps in sensation. It is admitted by all physiologists. We proceed to illustrate this function by one or two examples.
We bring the hand into contact with some body, and we have a sensation corresponding with the tangible properties of the substance touched. Here an impression is made upon the extremities of the nerves in the ends of the fingers ; this impression passes along the nerves of the hand and arm to the spinal marrow, and thence along the spinal marrow to the brain, where it produces a change which is recognized by the mind. We direct the eye towards an object; the light from that object makes an impression upon the retina, wliich impression passes along the optic nerve to the brain, and thus gives rise to a perception of the object.
Let us next turn our attention to voluntary motion. Volition as connected with motion is a peculiar act of the mind, which produces an effect upon the nervous systein, and through the nervous system upon the muscles; the muscles contract and produce motion. This is called voluntary motion.
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That part of the function, which belongs to the nervous system is accomplished in three successive steps, which occur in the reverse order of those of sensation. The mind puts fòrth a yolition ; this mental act produces an impression upon the brain, which impression is transmitted along the nerves to the muscles, which are thus made to contract, producing motion. Thus we have an impression upon the brain, the transmission of that effect along the nerves and the effect upon the muscles. For example; we will to raise an arm. The volition produces a peculiar change in the state of the brain ; this change in the brain propagates an influence along the spinal marrow and nerves to the muscles of the arm, which contract and raise the limb.
This mere glance at the functions of sensation and voluntary motion is sufficient to prepare us to witness without surprise the more unusual phenomena, which result from the union of a spiritual with a corporeal nature. In sensation, an impression is made upon the nervous extremities, and with the swiftness of thouglit notice of it is carried to the mind through the nerves and brain. In voluntary notion the mind puts forth a volition, and in an instant the mandate is obeyed by muscular contraction. Here, in the first instance, we see a physical effect, at the surface of the body, producing a simultaneous change in the state of the mind; in the second case, an act of the mind produces a physical effect upon the state of the muscles. These phenomena are so common, that they fail to attract our attention and to lead the mind to those trains of reflection, which enable us to reason correctly with regard to the more extraordinary phenomena of our mysterious being. But these simple facts, viewed in the light of sound philosophy, demonstrate the intimate sympathy between the body and the mind. We are prepared to expect, that the varying states of health and disease in the body will give a coloring to all the acts and emotions of the mind- now shedding the radiance of joy and hope on every scene in nature and on every creation of the imagination, and now casting over the present and the future the deep shades of melancholy. When we see a strong mental shock overpowering the physical frame and prostrating the frail body in the dust, we witness but another instance of the effects of that sympathy, which binds together spirit and matter. Who, that bas arrived at the meridian of life, has not witnessed, or experienced, the agitation of body, which accompanies that crowd of trembling thoughts and Auttering feelings, that rushes upon the youthful
mind, just as the decisive moment is at hand, which must settle the loss or gain of some long-desired object of pursuit ? Who does not know that the powers of the body ebb and flow with the rise and fall of the mental emotions,—as the mind wavers between hope and fear, between the bright anticipations of future good and the gloomy forebodings of evil ? “ A merry heart doeth good like medicine ; but a broken spirit drieth the bones.”
In the above imperfect view of the physiology of the nervous system, we have spoken of the brain as the instrument of the mind, as a primary organ in the functions of sensations and voluntary motion, in short as the great centre of psycho-physiological sympathy. We are now prepared to enter understandingly upon a more extended discussion of the reciprocal influences of the body and the mind. And in pursuing the subject, we shall endeavor so to arrange and present our conclusions, that they shall be clearly seen to be legitimate deductions from the foregoing propositions.
1. As the brain performs an important office in the functions of sensation and voluntary motion, we should expect, that any change in the state of that organ would be accompanied with a corresponding modification of those functions. Accordingly we observe, that compression of the brain embarrasses or suspends both of these functions. There are other states of the brain which produce exactly the opposite effects. In cerebral inflammation, a feeble light sometimes produces an impression, which is painfully intense, and ordinary sounds are so magnified as to be with difficulty borne. Some diseases of the brain are attended with frantic ravings and exhibitions of almost superhuman muscular strength. A remarkable instance of the effect of cerebral disease in giving increased intensity to the sensations, is recorded by Buffon in his Histoire Naturelle de l'Homme. It was the case of a priest by the name of Blanchet, curé de la Réolle en Guyenne, who passed through a violent fit of insanity, and after his recovery, wrote an account of the feelings which he had experienced. Blanchet thus describes the state of his sensations during the attack. “ In this violent malady my senses rose to an excess of delicacy and sensibility, that subjected me alternately to the keepest suffering and the most exquisite pleasure. The light seemed sometimes to dart against my eyes with such splendor and vividness, that I was unable to support its presence.
.. The sense of hearing also had its accesses and excesses. It was at certain times in such a condition, that the least sound jarred upon the ear, (l'é branlait)—so delicate and so sensible, that the gentlest undulations of the air became audible sounds. The sound of brass was especially insupportable; the suffering wbich it caused me was beyond expression. When I heard the ringing of the bell, which was unfortunately too near to me, it seemed to detach itself from the steeple of the church and to rise to the vault of heaven, with which forming one single body and the same instrument, it resounded with a terrific noise, whose shock was so terrible, that I imagined, that all the planets, which are suspended in the immensity of space, were disordered by it, and had fallen upon our eartli, making with it one mass of ruins. . . The other senses, the taste, the smell, etc., had their vicissitudes of pleasure and pain. I seemed at times to perceive odors and delicious perfumes, whose exquisite savors peither nature nor the art of the chemist could equal. At other times insupportable odors, nauseous and bitter tastes drove me almost to desperation. Even the sense of touch was affected with these extremes of pleasure and pain.” There can be no doubt, in this case, that the preternatural state of the senses arose from the sanje state of the brain, that caused the mental derangement.
We may next notice that class of sensations, which are not preceded or accompanied by any external impression. These are readily accounted for by supposing, that they result from peculiar conditions of the brain. We have seen that a peculiar state of the brain is the last step in the physiology of sensation, and an essential prerequisite 10 perception. Now if any internal cause should produce the same state of the brain, which results from an external impression, no possible reason can be given why the sensation and perception should not be the same as those resulting from an external impression. Thus an individual would seem to perceive external objects, and he would be unable directly to distinguish these mere states of the brain from those objects.
Dreaming furnishes apt illustrations of this principle. Here the brain passes through the same states, which are produced by converse with the external world, while awake. That dreams often result from the state of the physical system is proved by the fact, that indigestible food, taken late in the evening, frequently causes distressing dreams. Sometimes a narcotic medicine, while it composes to slumber, produces a state of dreamy happiness, with such vivid enjoyment, that the patient on awaking can hardly realize that he has been asleep. In both of these instances the brain is undoubtedly drawn into sympathy with other parts of the body, and thus gives rise to the dreams. In those instances, in which dreams seem to grow out of mental excitement, it is not improbable that the agitation of the mind produces a disturbance of the functions of the brain, and that this disturbed condition of the brain is the proximate cause of the dreaming.
In the delirium of fevers, and often in insanity, the mind mistakes the mere states of the brain for external objects. The case of Nicolai is familiar to most persons of any considerable reading. Esquirol, in the article Démonomanie of the Dictionaire des Sciences Medicales, thus describes the commencement of an attack of insanity. “M—, a woolen spinster, as she was returning from a long walk, became fatigued and lay down upon the ground to rest; in a short time she felt a motion in ber head and heard a noise like that of a spinning wheel.” In this case the apparent sound of the wheel evidently resulted from the brain's assuming the same state, into which it had before been brought by the real sound. The same author speaks of a young female under bis care in the hospital La Salpétrière, who, among other hallucinations, labored' under that of the sense of smell. She would frequently request the removal of the cause of some disagreeable odor ; at other times she spoke of enjoying the most fragrant perfumes, although in neither case was there any odoriferous body near. It is a circumstance worthy of remark in the account given of this female, that she had lost the sense of smell, so as to be insensible of the presence of natural odors, while the disordered state of her brain was giving her the most vivid perceptions of odors, when none were present to impress the organ of smell. Esquirol also mentions a melancholic patient under his charge, who was subject to a very singular illusion of the sense of bearing. His thoughts were accompanied by their audible expression. A voice seemed to pronounce bis thoughts as they flowed along; or as he said " he thought with a loud voice."
In illusions of this kind the sight is the sense, which is most frequently in fault; and its mistakes are sometimes corrected by the more gross and material sense of touch, assisted by the muscular sense, as when an apparent object of sight proves to be an illusion by its want of tangible properties. But when the salutary operations of the will and the judgment become embarrassed by disorders of the brain, when the function of external sensation is suspended, as in sleep, trance, etc., the mind neces