The laryngoscope : directions for its use, and practical illustrations of its value in the diagnosis and treatment of diseases of the throat and nose : two lectures delivered at the Royal College of Physicians / by George Johnson.

Date:: 1864

Credit: The laryngoscope : directions for its use, and practical illustrations of its value in the diagnosis and treatment of diseases of the throat and nose : two lectures delivered at the Royal College of Physicians / by George Johnson. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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$left Eustacliian tube ; also great swelling of the middle and inferior turbinated bones ; but no polypus, nor any tumour which an operation could have re- moved or lessened. Note.—Mr. Ernest Hart, ophthalmic surgeon to St. Mary's Hospital, has been good enough to send me, at my request, the following note on Oylitlialmosco])]) as conqnired with Lcvryngoscopij. I am happy to avail myself of his clear statement of the optical principles which render a perforated reflector necessary in the one case and not in the other. The light which penetrates the eye is not wholly absorbed by the choroidal pigment, and must there- fore pass out again; and, obviously, if the eye of an observer were brought into such a position as to receive these rays which emerge, he would see the image of the tunics behind the retina, which act as the reflecting screen. But as the eye is an optical apparatus composed of refracting media (lenses), the rays in passing out are refracted anew, and the image of the retina is formed in the air (and according to the lad) of conj'ugated foci) on the same side as the luminous object, and at a distance regulated by the accommodation of the eye, the distance of the object, and the shape which the lens of the eye assumes, for the purposes of distinct vision. Hence, if a light W'ere placed in front of an eye, and the head of an observer could be interposed between that light and the eye to be observed, he should, at the distance of distinct vision, be able to see the retina by virtue of its reflected image. But the head of the observer stops the light from entering. This difficulty, how- ever, is got over by putting a light by the side of the$