Obrázky na stránke
PDF
ePub

repetition of such observations and experiments as Cheselden made, would, I imagined, be greatly facilitated, by the total deafness of the patient in question; the judgments which a

Mr. Ware afterwards informs us, that he held a letter before his patient, at "the distance of about twelve inches, when he told him, after a short hesitation, "that it was a piece of paper; that it was square, which he knew by its corners, " and that it was longer in one direction than it was in the other."-"I then, (says he) showed him a small oblong band-box, covered with red leather; which he "said was red, and square, and pointed at once to its four corners. The observ

66

66

ation, however, which appeared to me most remarkable, was, that which relat"ed to a white stone-mug; which he first called a white basin, but, soon after, recollecting himself, said it was a mug, because it had a handle."

66

[ocr errors]

Of the correctness and fidelity of this statement, I have not the slightest doubt. But the only inference which can, with certainty, be deduced from it is, that the patient saw too well before the operation, to make his perceptions afterwards of any value for deciding the point in question. If he was able to recognise a green cloth, and a piece of white paper, the very moment that the bandage was removed, the degree of sight which he possessed previous to Mr. Ware's acquaintance with him, must have been such as to furnish him with a variety of sensations, quite sufficient to serve as materials for an imperfect visual language;—a language, if not accurately significant of comparative distances from the eye, at least fully adequate to convey, through the channel of that organ, the intimation of distance in general, or of what Berkely calls outness;-perhaps, also, some indistinct perception of diversities of visible figure. The slightest, and, to us, the most evanescent shades of difference in these sensations, will, we may be assured, become in the case of such an individual, signs of all the various changes in the state of surrounding objects, with which they have any connexion.

Having mentioned, on this occasion, the name of Mr. Ware, I think it but justice to him to add, that he does not appear to me to be himself disposed to push his argument against Cheselden so far as has been apprehended by some later writers. In the following passages, he not only seems to admit the truth of that optical principle which he has been generally understood to controvert, but even points at the same explanation which I have already suggested, of the apparent inconsistency between his own experience and that of his predecessor.

"I beg leave (says he) to add further, that on making inquiries of two children, "between seven and eight years of age, now under my care, both of whom have

been blind from birth, and on whom no operation has yet been performed, I "find that the knowledge they have of colours, limited as it is, is sufficient to en"able them to tell whether coloured objects be brought nearer to, or carried far"ther from them; for instance, whether they are at the distance of two inches or 'four inches from their eyes.

"I am aware, that these observations not only differ from those that are related "of Mr. Cheselden's patient, but appear, on the first statement, to oppose a prin

66

ciple in optics, which I believe is commonly and justly admitted, that the sen

"6

ses of sight and feeling have no other connexion but that which is formed by experience; and, therefore, that the ideas derived from feeling, can have no pow

66

66

"6

er to direct the judgment, with respect either to the distance or form of visible objects. It should be recollected, however, that persons who have cataracts in "their eyes, are not, in strictness of speech, blind, though they are deprived of "all useful sight. The instances I have adduced prove, that the knowledge they "have of colours is sufficient to give them some idea of distance, even in their "darkest state. When, therefore, their sight is cleared by the removal of the

68

opaque crystalline which intercepted the light, and the colour of objects is thereby made to appear stronger, will it be difficult or unphilosophical to conceive, "that their ideas of distance will be strengthened, and so far extended, as to give "them a knowledge even of the outline and figure of those objects with the colour "of which they were previously acquainted ?"

blind man is enabled to form of distances (at least of small distances) by the ear, approaching, in point of accuracy, very nearly to those which we are accustomed to form by means of the eye. I had once occasion to witness the precision with which Mr. Gough of Kendal (by far the most intelligent and ingenious person, born blind, whom I have happened to meet with) guessed at the dimensions of a large room, a few minutes after he had entered it. The error he committed was a mere trifle; not exceeding what might have been expected from the practised eye of a joiner or of an architect. It is not every operator, however dexterous in his own art, who can be expected to attend sufficiently to these collateral circumstances, or to be fully aware of the difficulty which a blind person, suddenly put in possession of a new sense, must experience, when he attempts to distinguish, in his estimates of distances, the perceptions of the eye from those of the ear or of the nostrils. Something of the same kind, indeed, or at least strikingly ana logous to it, happens every moment to ourselves, in the judg ments we pronounce on the beauty or deformity of visible objects, without any suspicion on our part, how much these judg ments are influenced by co-existent impressions of odour or of sound.

In consequence of this view of the subject, I had been led by the first general outline which I received of this occurrence, to indulge a hope that the peculiarities of the case might offer some facilities which had not been before experienced, for establishing, by palpable and incontestible proofs, the distinction between the original and the acquired perceptions of sight; while, at the same time, the inability of the patient to answer, by speech, the queries which might be proposed to him with respect to the new world to which he had been so recently introduced, would, I conceived, by drawing the attention of those around him to other signs of a less ambiguous nature, place the results of their observations beyond the reach of controversy. Not that, even upon this supposition, every difficulty would have been removed; inasmuch as intimations concerning distance may be occasionally conveyed to a blind man, not only by the sense of smell, but by some of those feelings which are commonly referred to the sense of Touch.* In observing, accordingly, the first visual perceptions even of a patient born deaf as well as blind, some very nice attentions

[

* The blind man of Puiseaux (mentioned by Diderot) judged of his distance from the fire-place by the degree of heat; and of his approach to any solid obsta cle, by the action or pulse of the air upon his face. The same thing is recorded of Dr. Sanderson by his successor Mr. Colson.

would be necessary for ascertaining the truth. But what proportion do these bear to the numerous and refined precautions which become indispensable, where the patient is reminded by every query which is addressed to his ear, of the distance and and relative position of the questioner? Justly might Diderot say," Preparer et interroger un aveugle né n'eût point "été une occupation indigne des talens réunis de Newton, "Descartes, Locke, et Leibniz."-I mention this, because, from the great degree of perfection to which this branch of surgery has been lately carried, the increasing number of such cases may be expected to multiply daily the opportunities of philosophical experiment; and it is of importance, that those who may have the good fortune to enjoy them, should be fully apprized of the delicacy and the complexity of the phenomena which they have to observe and to record.

*

In giving way to these speculations, I had proceeded on the supposition, that the blindness of the patient was complete; not sufficiently attending to (what was long ago remarked by Cheselden) the qualified sense in which the word blindness is understood by surgical operators. "Though this gentleman "was blind," says Cheselden, speaking of the patient whose case he has so well described,) "as is said of all persons who "have ripe cataracts, yet they are never so blind, from that "cause, but that they can discern day from night; and, for "the most part, in a strong light, distinguish black, white, "and scarlet; but they cannot perceive the shape of any thing.. "Thus it was with this young gentleman." The case I have since found to have been the same, and in a degree considerably greater, with the boy who has given occasion to this memoir; insomuch that his condition seems to have approached much nearer to that of Mr. Ware's patient than to that of Cheselden's. "At the time of life" (Mr. Wardrop observes) “ when "this boy began to walk, he seemed to be attracted by bright "and dazzling colours; and though every thing connected "with his history appears to prove that he derived little infor"mation from the organ of sight, yet he received from it "much sensual gratification.

"He used to hold between his eye and luminous objects, "such bodies as he had found to increase, by their interposi"tion, the quantity of light; and it was one of his chief amuse"ment's to concentrate the sun's rays by means of pieces of "glass, transparent pebbles, or similar substances, which he

For the assistance of those to whom such a subject of observation may occur, some judicious hints are suggested in the Lettre sur les Aveugles à l'usage de ceux qui voient.

"held between his eye and the light, and turned about in va"rious directions. These, too, he would often break with his "teeth, and give them that form which seemed to please him "most. There were other modes by which he was in the ha"bit of gratifying this fondness for light. He would retire to "any out-house, or too any room within his reach, shut the "windows and doors, and remain there for some considerable "time, with his eyes fixed on some small hole or chink which "admitted the sun's rays, eagerly catching them. He would ❝also, during the winter nights, often retire to a dark corner "of the room, and kindle a light for his amusement. On these ❝occasions, as well as in the gratification of his other senses, "his countenance and gestures displayed a most interesting "avidity and curiosity.

"It was difficult, if not impossible, to ascertain with preci"sion, the degree of sight which he enjoyed; but from the "preternatural acuteness which his senses of touch and smell "had acquired, in consequence of their being habitually em"ployed to collect that information for which the sight is pe"culiarly adapted, it may be presumed with confidence, that "he derived little, if any assistance from his eyes, as organs of "vision. The appearances of disease, besides, in the eyes, were "such as to render it in the highest degree probable, that they "enabled him merely to distinguish colours, and differences "in the intensity of light."

From this history of the patient's previous situation, it appeared evident that his case was not of such a sort as to afford an opportunity of bringing Cheselden's conclusions to the test. On the contrary, his habits of observation, and even of experiment, on his visual sensations, combined with the singular acuteness and discrimination of his olfactory perceptions, rendered it almost certain that the results of a succesful operation on his eyes would be similar to those described in Mr Ware's paper. Such, accordingly, has, in point of fact, been the issue of this new experiment ;-in describing which, however, I must remark, to the honour of Mr. Wardrop, as a cautious and philosophical observer, he has abstained from drawing the slightest inference to the prejudice of Cheselden's statement; —a statement nothing can disprove till a case shall occur of a patient cured of total, or almost total blindness; and till this case shall be observed and examined with all the nice precautions which so delicate and complicated a phenomenon demands.

I shall not follow Mr. Wardrop through the details of the surgical operation; in performing which, he was forced, by the

peculiar circumstances of his patient, to employ a mechanical apparatus, for fixing his body and head in an immovable posture. I flatter myself that he will soon communicate to the public a history of the whole case; and I should be sorry to deprive his memoir of any part of its interest.* The general results alone are connected with the objects which I have at present in view; and these I shall take the liberty to state in Mr. Wardrop's words.

"When the operation was finished, he expressed great satis"faction; gazed around him, and appeared to distinguish ob"jects. This, however, could not be ascertained in a manner "quite satisfactory, as it would have been prejudicial to his re"covery to make any experiments; but it could be perceived "from the change in the expression of his countenance. His "eye, accordingly, being covered up, he was carried home, "and put to bed in a dark room; after which he was bled in "the arm. . .

.....

"On the fourth day, I examined the eye accurately, and ob"served the state of his vision. I found that the crystalline "lens (which had been pushed upwards and backwards) had "altered its situation since the operation, and could be again "distinguished, covering about one-fourth of the upper edge of "the pupil. The other part of the pupil was quite transpa"rent, and all the blood which was effused into the anterior "chamber during the operation was now absorbed. On making "trial if he could distinguish any object, he readily discovered "a book, or any similar thing, placed on the coverlet of the "bed; and in many of his attempts, he seemed to judge pretty "accurately of their distance.

[ocr errors]

"On the fifth day he got out of bed, and was brought into "a room having an equal and moderate light. He walked "about the room readily; and the expression of his counte"nance was much altered, having acquired that look which in'dicated the enjoyment of vision. Indeed, he always walked "about, before the operation, with much freedom; and even on a very rugged and unequal road, he did not appear to suffer "in the least from any jolting.

66

"He appeared well acquainted with the furniture of the room, having lived in it several days previous to the opera"tion; but though he evidently distinguished, and attempted

This very curious and interesting Memoir has since been published under the title of "History of James Mitchell, a Boy born Blind and Deaf, with an Account "of the Operation performed for the Recovery of his Sight, by James Wardrop, F. R. S. Edin."-London, printed for John Murray, Albemarle Street, &c. &c.

1813.

« PredošláPokračovať »