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539 suffering in parts quite remote from where they are situated. Indeed, a large proportion of what are usually denominated sympathetic pains, receive their explanation from this same organic law, in consequence of which the sensations produced by the irritation of a nerve at any point in its course, are uniformly referred to the part or parts where the branches of that nerve terminate.
It deserves further to be remarked in this connection, that each nerve is so constituted as to be capable of awakening but a single class of sensations. The optic nerve, whatever the stimulus applied to it, can awaken only sensations of color. No pain is occasioned by its mechanical irritation; there is no consciousness even of such irrita. tion; all that the individual perceives, is a succession of luminous flashes of greater or less vividness. The effect is the same when discharges of electricity are made to take place along its fibres. By pressure properly applied to the ball of the eye and through that to the nerve, all the colors of the rainbow may be produced. Even gastric disturbance, when extending its influence to this organ, awakens only the perception of brilliant luminous points and spectra. So also the auditory nerve is capable of exciting no other sensations than those of sound. Irritation or pressure communicated to it through the surrounding parts, does not occasion pain but simply tinnitus aurium, or ringing in the ears; and as the passage of electricity along the optic nerve produces an effect nearly resembling lightning; so the transmission of the same fluid along the auditory nerve awakens a sensation that might be mistaken for thunder. The same is true of the nerves of smell, of taste, and of feeling. Each of these is precisely fitted in all respects for the performance of its own proper office, but no one of them is capable of performing under any circumstances the office of another. As well might the elements themselves interchange their respective functions and properties.
We next pass to a brief review of the phenomena of perception. These, though less immediately perhaps, are as really dependent upon the action of the brain and nerves, as those of sensation.
In fact, there is reason to believe that they are always either preceded, or attended by sensation, and are consequently subject in their manifestation to the same organic laws. They are commonly divided by writers on mental philosophy into two classes; the first, including all our original perceptions, or those which are supposed to have been connected with the first use of our perceptive faculties, and the second and far more numerous class embracing all those ideas which though not originally derived from the senses, have become through the power of habit, indissolubly associated with their exercise. The dis
tinction is undoubtedly a just one, and should be borne in mind, if we would forni correct views in regard to the sources of our knowledge. For, while on the one hand, it would seem clear that if our sensations had originally suggested nothing beyond themselves, they must forever have remained thus isolated, on the other hand it is equally clear, that a very large proportion of the ideas, which they at present serve to introduce, are connected with them only by the ties of association. For the true origin of these, we must look to other classes of sensations, or to the deductions of reason, or to the teachings of experience, or to all of these different sources combined. Of the numerous and varied perceptions which we now have through the eye, it is probable that only those of color and figure and the latter with but two dimensions, first entered the mind through that organ. All the others, whether of form, size and distance, or of the numerous physical conditions and properties of bodies, so instantly recognized by their appearance, have been gradually built up upon these. Although in reality only associated conceptions, they are suggested so immediately and held before the mind so steadily, that we ordinarily mistake their character and confound them with our perceptions. By ful analysis, however, of the assemblage of ideas called up by looking at any familiar object, it is not difficult to distinguish them; and in endeavoring to do so, we may derive assistance from recollecting that the same ideas are awakened by the picture of that object, which consists of nothing but different shades of color spread upon a plane surface. That a large part of the information received at present through the eye, entered the mind originally through other channels, is moreover evident from what we know of those persons who have seen for the first time after they have arrived at an age enabling them to notice and describe their sensations. Such persons have been found uniformly unable to recognize by sight the objects, with which they were most familiar through the other senses ; and it has been only by a long course of experience that they have learned to connect the perceptions which they have through their newly acquired faculty with the corresponding ones of touch, so as to refer both to the same external object. The boy who was couched by Cheselden, at first saw everything flat. The walls of the room, the beams projecting from them, and even the intervening articles of furniture, seemed to be in the same plane; nor could he distinguish from one another, by their appearance, the objects immediately around him, which he had known and been accustomed to handle from his infancy. “He was acquainted with a dog and cat by feeling, but could not remember their respective characters when he saw them. One day when thus puzzled, 1849.)
Formation of Habits.
he took up the cat in his arms and felt her attentively, so as to asscciate the two sets of ideas; and then setting her down, said, ‘so, puss, I shall know you another time.'” Dr. Wm. B. Carpenter, in his excellent treatise on physiology, mentions the case of a boy upon whom he operated, and who for some time after he had acquired the power of seeing, was accustomed when in haste and among familiar objects to close his eyes, so little was the assistance derived from them, and direct bis steps by feeling.
To draw the precise line of distinction between our original and our acquired perceptions, and to trace each of the latter to its true source, is one of the most difficult tasks of the mental philosopher ; and as it is in no way essential to the proper elucidation of our subject, we do not propose to enter upon it. We would rather invite the attention of the reader to a brief consideration of the feature of the human constitution, in which this association of ideas,-this blending of the knowledge derived from one sense with the perceptions awakened through another, has its origin. On examination, it will be found to proceed, we think, from a law of our nature which may be expressed as follows. Whenever any two bodily or mental acts have been many times performed either simultaneously or successively, the repetition of one of these acts creates a tendency towards the other ; and so strong does the tie between the two at length become, that the performance of one is invariably accompanied or followed by that of the other, without any conscious effort on our part. This law, which would seem also to hold, though not perhaps to so great an extent, of the bodily and mental affections or states, lies at the foundation of all our habits. Without it, indeed, we should be wholly incapable of habit, that chief method and instrument of every form of human improvement. Without this we should be unable to fit ourselves for any of the avocations or duties of life. We could not learn to act or to think, to talk or to walk. We could not rise in the scale of existence even to a level with the brutes, many of which are to a certain extent susceptible of education. Nay, we should be incapable of making provision for the supply of our natural wants, and the race itself would become extinct.
Illustrations of this great and fundamental law of our nature, may be drawn from any of the trades, arts, professions or occupations in which men are engaged. Preparation for them, consists not so much in the acquisition of knowledge as in the formation of habits. It is not the committing of rules or the understanding of principles even, but practice that makes perfect. He who would learn to play upon a musical instrument, will find the most difficult part of his task to conVol. VI. No. 23.
sist in chaining together the varied muscular contractions necessary for the execution of an air, so that when the first movement has been made, the others shall spontaneously follow, with due regard to order and time. When this point has at length been attained, he may withdraw his immediate attention from the instrument and become interested in other subjects, and engage in conversation upon them, and the keys continue to be rightly touched, and the harmonies to flow on. In learning to speak a language, the chief labor consists, not in mastering its vocabulary, nor yet in acquiring a knowledge of the laws in accordance with which its words are combined in the construction of sentences, but in linking them to the corresponding ideas, so that these on arising in the mind shall instantly suggest them, and in forming the organs of articulation to those habits of associated action which are necessary to their ready and Auent utterance. So also in the different kinds of mental training, the mos: important as well as the most difficult end to be attained, is not the acquisition of knowledge, but the power of using it-not the simple storing of the mind with ideas, but the connecting of these ideas with one another according to their natural relations, so that they shall spontaneously flow out in continuous trains of just and vigorous thought; and this concatenation can be effected only by causing them repeatedly to pass through the mind in the order or orders in which we would have them associated.
We are aware that writers on this subject are accustomed to speak of contiguity of time and place, of the relations of cause and effect, of reseinblance and of contrast, as principles of association; and that our ideas are connected with one another very generally in accordance with these relations, is unquestionably true. But, that these relations constitute the real tie between them and are the immediate cause of that connection, is a very different and we think far more doubtful proposition. Indeed, such a notion can be founded only on the supposition that our ideas are actual existences stored away in the mind and so chained together by certain constitutional affinities, that when any one of them is brought under review, it draws the others along after it. The moment we conceive of them in their true character, as states or affections of the spirit, having their origin either in its own action or in that of the organism with which it is connected, we see that like all other effects, they can be associated only through the causes which produce them. The real, physical connection must exist between these, and if we mistake not, is to be found in those ties which habit has established among the different bodily and spiritual activities concerned in the evolution of the mental phenome
543 The reason, therefore, why our ideas are connected with one another very generally in accordance with the above relations is, that the organic acts upon which they depend have been again and again repeated, either voluntarily or through the influence of circumstances, in the order of those relations, until they at length have become chained together by habit, and'the series when once started continues to move on, without the stimulus of outward impressions and without aid from the will. In the same manner, our perceptions acquired through the different senses, become linked to one another so that when any one class is awakened by the object to which they relate addressing that particular sense, the others are immediately introduced by the simultaneous action of the appropriate organs; and so close is the connection between the different classes of the associated group, that as we have already intimated, there is frequently much difficulty in separating them and determining which are the original and which the acquired perceptions. The great English dramatist appears to us, to have had a far more just conception of the true cause or principle of association among our ideas, than we usually find in the books of philosophy. The following passage from the opening scene in the Merchant of Venice, presents a fine illustration of the train of thought following the lines of connection, which interest and habit have established, and not the relations subsisting among the ideas themselves. Salarino is describing the anxiety and apprehensions which would prey upon his spirit, had he “such venture" at sea as Antonio.
My wind, cooling my broth,
Why the continued repetition of a series of bodily or mental acts binds those acts together, so that the series once commenced flows on irrespective of any effort on our part, is a question which our present knowledge of the human constitution affords no means of an