On the mechanism of the movements of the iris / by J. N. Langley and H. K. Anderson.

  • Langley, J. N. (John Newport), 1852-1925.
Date:
[1892]
Catalogue details

Licence: Public Domain Mark

Credit: On the mechanism of the movements of the iris / by J. N. Langley and H. K. Anderson. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    A similar line of observation shows, that the dilation which follows stimulation of the sympathetic can be produced independently of a diminution in blood supply to the iris. This was shown fairly conclusively by the experiments of Budge and Waller* (1851), and of Budge (1855). It is true that Budge and Waller did not make their experiments with any view to the theory we are now considering; vaso-motor nerves were in fact then undis- covered. But they found that stimulation of the sympathetic for some time after death caused dilation of the pupil; since there was no arterial blood-pressure, and since the stimulation was repeated more than once, it is in the highest degree unlikely, that variations in the amount of blood in the iridic vessels could have been the cause of the dilation of the pupil. The experiment, with varying degrees of regard for the points to be attended to, has often been made in later times and perhaps most satisfactorily by Fran9ois-Franck (1880), who after bleeding an animal to death, stimulated the sympatlietic at intervals several times in succession, obtaining each time dilation with intervening return to the constricted state. The observation is easily made, and further evidence is offered by the fact that dilation can be produced in an extirpated eye by stimu- lating a long ciliary nerve. Although it is certain that the sympathetic is capable of causing a dilation of the pupil in some other way than by decreasing the amount of blood in the iris, it seems, on general grounds, reasonable to suppose that variation in the state of turgescence of the blood-vessels of the iris should have a not inconsiderable effect; and this view is widely believed. Nevertheless, it appears to us that the view has no satisfactory founda- tion, and that the tone of the muscular part of the iris is sufficient normally to prevent the tendency to movement due to variations in the amount of blood in the iris. Waller^ pointed out that pressing the eye of a white rat so as to make the iris bloodless had no effect on the pupil. The considerable variation in blood-pressure caused by stimula- ting the central end of the depressor, or the lower cut end of the spinal cord, usually causes no alteration in the size of the pupil. Brown- Sequard^ noticed that injecting blood into the ophthalmic artery caused but a barely appreciable constriction of the pupil. We have injected a ^ Budge et Waller. Comptes Rendus de VAcad. des Sciences, T. xxxiii. p. 418, 1851. 2 Waller. Comptes Rendus de VAcad. des Sciences, T. xliii. p. 659, 1856. 3 Brown-Sequard. Journal de la Physiologic, ii. p. 452, 1859.