The Senses and the Mind

by Anonymous

"The rapidity of the mental processes seems to require an electric, or some similar medium, by which they may be effected in connexion with the body, since they result so instantaneously, that the will to move, for instance, and the motion, are simultaneous. Professor Wheatstone has proved, that electricity, like light, travels at the rate of 192,000 miles in a second, and this appears to be an agency sufficiently subtle to answer all the purposes of the soul as an active being. Probably electricity and light are but one agent, acting under different relations. It is interesting to consider ourselves, by each act of our will, as operating upon embodied light; but whatever be the immediate agency between mind and muscle, it is vastly more interesting to know, that willing being is something as really and distinctly existing as the light itself, but in its nature infinitely more subtilely and exquisitely constituted, since it is indivisably and inscrutinably associated with the Being who said, Let light be, and light was!"

"If we advance further in contemplating our mental existence with the body, we shall more clearly perceive that the body itself is not the cause, but the instrument of mind. In order that it should be a ready instrument, it is, as we see, constructed on electro-magnetic principles, so that it serves the purposes of the mind in many spontaneous actions, without even awakening consciousness. Whatever is essential to the processes of life is carried on in the economy without our consent; and until some demand is made by the body, requiring our voluntary interference for the removal of inconvenience, or the supply of aliment, our attention is not so far attracted to the body as that our desires are distinctly perceived to arise from its state. Thus, we feel hunger or thirst, and use means for their removal. But our emotions and affections are at all times influenced by bodily condition, and in many respects may be traced to a physical origin. They are so far involuntary, that their causes are in operation before we are aware, and they are apt to evince their power against our wills; yet reason is tested by their presence, and she prevails over them, in proportion to the clear perception and experience of spiritual motives, or those moral convictions which arise from religious enlightenment. Were it not that our connexion with the body subjects us to feelings against which we are conscientiously and reasonably required to contend, we should be incapable of that self consciousness by which we distinguish ourselves from our bodies. In fact, those who find no other inducement to thought and action than the body affords, are really incapable of apprehending any other than bodily existence, and they live not according to spiritual but sensual motive."[28]

[28] Dr. George Moore.

Granting the truth, or the approximation to truth, of the foregoing theory, it is evident, not only that whatever alters the force of the electro-galvanic currents of which the nerves are conductors, alters the condition of the mind in relation to the body, thus making impressions weaker or stronger; but that whatever deranges the tone or "timbre" of the nerves themselves, produces mental illusions which are sometimes of a temporary, sometimes of a permanent character. For example, in derangements of the digestive organs, partial loss of sight in one or both eyes, the appearance of black motes, specks, or flies floating in the atmosphere—coloured wavy lines or zigzags—nay, even strange faces, sometimes grotesque, sometimes terrific, palpable to vision like the air-drawn dagger of Macbeth, are by no means unfrequent phenomena.

But, besides these transitory effects of nervous derangement, there are others dependent upon a permanent condition of the nerves, which is not well understood. For example, some persons are incapable of distinguishing between certain colours, while at the same time there is no defect in the construction of the eye, as an optical instrument. Sir J. Herschell examined the eyes of a person affected with this peculiarity, and satisfied himself that all the prismatic rays had the power of affecting them with the sensation of light, and of producing distinct vision. Hence, therefore, as he observes, "the defect arises from no insensibility of the retina to rays of any particular refrangibility, nor to any colouring matter in the humours of the eye preventing certain rays from reaching the retina, as has been ingeniously supposed, but from a defect in the sensorium, by which it is rendered incapable of appreciating exactly those differences between rays on which their colour depends."

The degree of defect in these singular cases is variable, nor are the colours which the sensorium cannot appreciate by any means always the same. Generally, however, red and green are the colours which are not discerned, while blue and yellow seldom fail to make a due impression. Seebeck, on somewhat vague grounds, as we think, divides persons labouring under this defect of vision into two classes. The first consists of individuals who have a very imperfect power of distinguishing the impressions of colours generally; in these, at the same time, the defect is greatest with regard to red and green, these colours being not distinguishable from grey; blue is imperfectly distinguished, and yellow the most perfectly.

The second class consists of individuals who err with regard to the distinction of red from blue; and who, as in the first class, recognise yellow the best. It is not, as we have said, to the eye itself that we are to look for the cause of this defect, but to some mysterious peculiarity of the sensorium, or to some want of harmony between the brain and the optic nerves; but whether the failure is in the energia of the optic nerves, or in the sensorial power of the brain, we pretend not to say. We have, in fact, in this instance, as in so many others, only to confess our ignorance. It is scarcely needful for us to add, that this visual defect is irremediable.

But there are defects of vision dependent upon the structure of the eye itself, as an optical instrument; and under this head we may first notice myopia, or near-sightedness. Myopia results from an over-refractive condition of the eye, the rays of light passing from any object being brought to a focus in the vitreous chamber of that organ, before reaching or impinging on the retina. In this case, either the cornea or the crystalline lens is too convex, or both are in this condition, or the humours of the eye generally are too dense or too abundant, and the pupil is large. Persons thus affected see all objects indistinctly which are viewed at the ordinary distance of distinct vision, but objects held close to the eye are seen with microscopic accuracy. The distance from the eye, when in a normal state, at which objects are surveyed with the utmost distinctness, is from fifteen to twenty inches. An eye which cannot discern objects with ease and accuracy beyond ten inches, may be considered as myopic; but not unfrequently persons affected with myopia cannot regard an object with distinctness which is beyond four, three, two, or even one inch distant from the eye.

To myopic persons, objects brought within their sphere of vision appear magnified; a small type is read more easily than a large type; and, indeed, such eyes see better through a pin-hole in a card than when not thus assisted; the reason is, that the pupil, from its dilatation, admits too many rays of light, but by diminishing the aperture through which the rays of light are admitted, all but those which are the most direct are excluded, and the images on the retina will be, therefore, the more defined. On the same principle, myopic persons, when endeavouring to see distant objects, half close the eyelids, (hence the term myopia, from μύω, I shut, and ὤψ, an eye.) Myopic persons generally see better in the dusk, or at twilight, than others; and their sight, though short, is strong and good, often lasting. It has been asserted, that as the eye flattens in age, the vision of myopic persons will improve as they advance in life, and the theory, it must be acknowledged, seems feasible, but experience proves that this is not the case; indeed, it would appear that the myopia rather increases than diminishes.

Concave glasses greatly assist the myopic eye; they cause a divergence of the rays of light before entering the pupil, and thus counteract the over-refractive condition of that organ. The degree of concavity best suited to particular cases can only be determined by trials.