The histology of the eye / by John Whitaker Hulke.

  • John Hulke
Date:
[1869]
Catalogue details

Licence: Public Domain Mark

Credit: The histology of the eye / by John Whitaker Hulke. 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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    The Iris corresponds to the diaphragm in the cornea. Stretched across the anterior chamber, it stops out the most peripheral rays, which, in its absence, would pass through the edge of the lens, and in this way it lessens spherical aberration; then, by varying the size of the pupil, it regulates the quantity of Hght admitted to the retina; and, finally, it is an accessory of the apparatus of accommo- dation, although not in man an actual factor. The iris is essentially a muscular organ. The contraction and dilatation of the pupil are due to muscular irritability, and not to vascular erectility. Their continuance after the heart has ceased to beat, and even after the head has been severed from the body, are facts which place this beyond discussion. In mammalia, the muscular tissue is of the unstriped kind; while in birds and reptiles it is striped. One of the most useful chemical agents for demonstrating it is the chloride of palladium. The iris should be placed in a solution of this, containing from one-fourth to one-eighth per cent., until it acquires _ a deep straw tint. The palladium chloride hardens the tissue, without making it so granular and opaque as chromic acid does; and it beautifally preserves the nuclei. With this reagent, its demonstration is easy and certain in the eyes of white rabbits, where it is unobscured by pigment which conceals it in human eyes. The cells, which are not easily iadividually isolated, are long spindles containing a rod-hke nucleus. They resemble closely the cells of the larger organic muscles. The cells cohere iu small flat bands, and these again combine in larger bundles. In man, I believe also in Fig. 7. Iris of White Rabbit, prepared will) Chloride of Palladium, to show the disposition jnsoi vvnueMuu ,r f jij^ jjuscular Tissue. mammalia generally, in birds, and in reptiles, the muscular bundles are disposed in two sets, which have a radial and a cu-cular direction and constitute a sphincter and a dilator muscle of the pupil. (Fig. 7.)
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