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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    there is dilation of the pupil without any appreciable contraction of the vessels of the iris. On the stimulation of the sympathetic for a longer time, the vessels of the iris do not begin to contract until the maximum dilation of the pupil is nearly or even quite attained; and on cessation of the stimulus, the greater part of the constriction of the pupil is over before the dilation of the blood vessels begins. If the stimulation is much prolonged the iris begins slowly to constrict, although the vessels show no sign uf dilation, but after cessation of the stimulus, the return to normal is quicker with the blood vessels than with the pupil. There is in fact a similar difference in the time of dilation of pupil and constriction of blood vessels of the iris to that found by Arlt and by Fran9ois-Franck in the time of dilation of the blood vessels of the ear. We must, however, expressly state that on stimulating the cer- vical sympathetic, the contraction of the vessels of the iris, and the contraction of the vessels of the ear are often not synchronous; so that the state of the vessels of the iris cannot be safel}^ deduced from the state of the vessels of the ear. The independence of the two actions of the sympathetic on the iris can also be seen in the albino rabbit after injecting brucin (cf. above p. 576). It is true we have not obtained after giving brucin complete abolition of the action of the sympathetic on the pupil, with retention of its action on the blood vessels of the iris. But we obtained a stage in which the sympathetic caused a momentary slight dilation only of the pupil at the beginning of the stimulation and this was followed by complete pallor of the iris unaccompanied by a change in the pupil. When in this stage the sympathetic was stimulated two or three times in quick succes- sion, the second or third and later stimulations caused no dilation of the pupil. Making use of this fact we could obtain complete contraction of the arteries of the iris without any change in the size of the pupil. In the white rat the circulation in the iris can be seen better than in the rabbit; and, as in the rabbit, there is little difficulty in showing that the sympathetic causes dilation of the pupil in some other way than by causing a contraction of the vessels of the iris. We give a sketch of the arteries of a portion of the iris of a rat (a) before (6) after a momentary stimulation of the sympathetic (Fig. 8). In the albino rabbit and white rat, all the arteries of the iris examined under the microscope contracted and dilated simultaneously^ ^ When a constriction of the iridic arteries is brought about refiexly, the arteries of the major circle and the arteries radiating from it to the sphincter border do not necessarily constrict and dilate synchronously. PH. XIII. 38