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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    1. That dilation is due to the action of the sympathetic vaso- constrictor nerves. Griinhagen has perhaps been most concerned in bringing this theory into prominence. There are two ways in which the contraction of the blood-vessels of the iris, induced by the vaso-constrictor nerve-fibres, might bring about dilation of the pupil. (a) By decreasing the quantity of blood in the iris, so that it shrinks. This appears to be the method implied by the upholders of the theory. (h) By a longitudinal contraction of the radial arteries of the iris ; this contraction dragging the sphincter outwards. A marked longitu- dinal muscular coat has been described in some animals in the arteries of the iris. 2. That dilation of the pupil is caused by the contraction of radi- ally arranged muscular fibres. This view has been taken by Budge, Henle and many others. 3. That dilation of the pupil is caused by inhibition of the sphincter muscle. Griinhagen and Samkowy^ (1875) stated as a possibility that the sympathetic might be an * ErschlafFungsnerv' of the sphincter, but Griinhagen left the matter there, and appears to have adhered to the vascular theory. Fran^ois-Franck^ (1880) expressed his opinion, though not without reserve, that the sympathetic dilator nerves of the iris act in the same manner as the dilator nerves of the vessels, and suspend the activity of the constrictor nerves. Gaskell^ (1886) more definitely put forward the inhibitory theory, and since then it has found a good deal of support. The theory of course requires the presence of elastic tissue in the iris, which is more or less stretched except when the pupil is dilated to its full extent. It is conceivable that the sphincter should aid in the dilation of the pupil by actively elongating, but this view has not, so far as we know, been advanced. 4. It is possible that in certain circumstances, a certain degree of dilation of the pupil should be caused by a relaxation of the ciliary muscle. By such relaxation the elasticity of part of the ciliary region and the anterior part of the choroid would come into play, and pull backwards the iris. 1 Griinhagen u. Samkowy. Arch. f. d. ges. Physiol, x. p. 165, 1875. 2 Franpois-Franck. Travaux de Laboratoire de M. Marey, iv. p. 55, 1880. 3 Gaskell. This Journal, vii. p. 38, 1886 and Proc. Physiol. Soc. 1887, p. xxxi. (This Journal, ix. 1888.)