Description of a Totally Reflecting Prism, employed for illuminating the open cavities of the Body; with a view to facilitate the examination of Disease, and the application of remedial means in such situations; illustrated with an Ear" Speculum" or Prismatic Auriscope, adapted to this method of observation. By ADAM WARDEN, M.D., F.R.C.S.E. (With a Plate and Woodcut.) Communicated by the Royal Scottish Society of Arts.*

Having been present on repeated occasions at meetings of the Society of Arts, and appreciating highly their efforts to give an impulse to useful observation, and to its practical application to general purposes, I beg leave to present to their notice a method of illuminating the open cavities of the body, whereby the examination of disease and the application of remedial means in such situations may be facilitated.

As I had heard Monsieur Charles Dupin express himself to the Society of Arts of Paris, "Here, in the doctrine of parallel lines, the weaver and the carpenter are to see the secrets of their own art, and in the various expositions every artisan is to catch the application of the doctrine of his trade;" so, in listening, as a casual auditor at a late meeting of this society, to some notices of the useful application of prismatic reflection, an adaptation of a prism to the apparatus of surgery suggested itself to me, and is now submitted to inspection.

A short time before the meeting of this society above referred to, my attention was especially awakened to the difficulty attending the management of diseases in the open cavities of the body, by the experienced imperfections of the exist ing apparatus of aural surgery. The object of my present communication is to explain my attempt to improve that apparatus, by a new method of throwing light upon the parts to be examined, and it will readily appear that the arrangement proposed is equally applicable to any of the other open cavities. of the body. The manifold importance of the diseases of the ear, as affecting the valuable sense of hearing, and in their

* Read and exhibited to the Society on 22d April 1844.

more serious forms even endangering life itself, will be conceived, when it is mentioned that Valsalva, one of the most eminent anatomists of the last century, devoted sixteen years of a laborious life to their investigation, and to the composition of his treatise on the subject. His biographer, Morgagni, mentions that he performed an incredible number of dissections in this research. The great proportion of the diseases of this organ, and those of the most remediable kind, have their origin in the external auditory canal, and the tympanum at its termination-the vascular texture and the situation of those parts exposing them to the first attacks of disease, and, whence, in its unchecked progress, it is propagated to the complicated interior structures, to the bones and the brain.

The external auditory passage exceeds an inch in length, is curved in its course, and is commonly so beset with hairs as to prevent the view of its inward track and termination; but by the aid of a straight canula, or the common speculum, these obstacles to observation are readily obviated; sufficient light, however, to illuminate the passage, still remains the one desideratum, without which, to exhibit the actual condition of the membrane of the tympanum, the surgeon cannot pronounce as to the importance or curability of disease, nor resort, with confidence of its safety from danger, even to the popular remedy of the syringe. The instrument submitted to the Society, and represented in the Woodcut, is constructed upon the principle of illumination derived from prismatic reflection. It consists of separate portions: a straight handle, a a, five inches in length, terminating in a ring, b, of half an inch internal diameter, the ring grooved in its interior as a screw. To this screw are adapted four canule or straight tubes, c, of one, two, three, and four lines calibre, and another, d, of a funnel or tapering shape, applicable to the dimensions of the auditory canal at different ages and under different degrees of constriction resulting from disease; the wider mouthed canula is intended to be employed for preliminary exploration and removal of any accumulated cerumen obstructing the passage of the light, also for affording a proper field for the passage of instruments and other topical manipulation. The canulæ are an inch and a quarter in length, and terminate in blunted edges, to

prevent injury in their passage into the ear. From the middle of the straight handle, and at an angle with it of about 20°, arises a curved branch, e, inoveable in a pivot joint at f, toward either side of the handle. This branch forms a stalk, on which a prism of flint glass, g, is perched erect, to the level of the opening of the affixed canula. The prism rests in a metallic socket, and is made to revolve on its own axis at the touch of the finger, or to remain fixed in any desired position by the aid of a small clamping screw, h. The instrument is thus complete for use. The canula is to be introduced into the ear to be examined, the patient being seated by a table, having a good light of a gas jet or argand burner at a convenient distance to one side. The surgeon being placed opposite to the ear to be inspected, a face of the prism is turned towards the light, and it is made to revolve until the luminous spectrum is conveyed to the bottom of the canula, and to the surface sought to be observed. There is no difficulty in the adjustment of position, when the relations of the light and the object are ascertained by a little experience; and when this adjustment is made, the full and clear illumination of the object is at once obtained, and with a degree of brilliancy proportioned to the quantity of light employed in the particular observation. Where different circumstances require it, the intensity of the light may be artificially increased to any desired extent.

The principle or theory, as already mentioned, consists in total reflection. The light is received by one side of the prism, is reflected from the second side, and emerges by the third side to the object illuminated, as represented by the dotted lines x y z, and thus its view is revealed to the eye. The light afforded is nearly equivalent to the same candle or gas-light applied to the page of a book, or other familiar uses, so little of it is lost in its passage through the prism. The illumination is not preternatural or dazzling, such as would alter the real features of disease, but natural, and such as the eye is familiar with. The advantage of this unconcentrated natural light can only be fully appreciated by professional eyes; and I am persuaded that any method of concentrating light by lenses or converging mirrors, substituted for the prism, would not increase the serviceableness of the

instrument exhibited for medical examinations, but the reverse; and of this I speak from sufficient experiment.

The Society will understand that whilst this instrument is constructed so as to afford the utmost amount of light which the dimensions of the passage of the ear can admit, it is not intended to supersede the use of the speculum which generally bears Dr Kramer's name, the utility of which, in so far as that extends, is established by the concurrent experience of the profession; neither in the other applications of prismatic illumination which present themselves to me, would I be understood to depreciate existing apparatus, when I suggest such modifications as may increase or extend their efficiency. Indeed, it has been my aim, in constructing the other adaptations of the prism, to frame these so as to be a ready appendage of all the different forms of specula in the hands of the profession. The importance attached by professional persons to the existing very imperfect methods of illuminating the ear may be estimated by a reference to Dr Kramer's Treatise on the Ear, translated by Dr Bennet, which describes his ingenious efforts to effect this end in these terms. "In order to obviate the above objections (to all other forms of illumination) as far as possible, I have constructed the following apparatus. The principal part is an argand lamp, with a thick cylindrical wick, the reservoir of oil being placed behind the box next to be described. This box is constructed of tinplate, the inner surface of which is painted black in order to prevent any reflection of the light. It covers the lamp so as completely to enclose the flame, the lamp-glass passing through an opening in the top. At a convenient distance from the flame, and behind it, against the inside of the back of the box, there is a plated concave mirror. In the anterior face of the box there is inserted a tin tube fourteen inches in length, which is likewise blackened inside, and each extremity is provided with a double convex lens two inches and a half in diameter. The argand lamp throws its powerful mass of light against the concave mirror, whence the rays are reflected through the first convex lens, along the tube and through the second convex lens. The luminous rays are thus collected into an intensely bright focus of the size of a shilling, at a distance from