Our eyes, and how to take care of them / by Henry W. Williams.

  • Williams, Henry W. (Henry Willard), 1821-1895.
Date:
1871
Catalogue details

Licence: Public Domain Mark

Credit: Our eyes, and how to take care of them / by Henry W. Williams. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    choroid, this curtain is lined with dark color- ing-matter, not only to absorb any irregularly refracted rays, and prevent reflections from side to side within the globe, but to exclude the entrance of light through the*coats of the eye, except in the direction most suitable for refraction, — through the cornea and pupil. To complete the noble endowment of ca- pacities, the eye has yet another power. It is a self-regulating optical instrument. We may turn our eyes from the printed page to gaze at a distance, or withdraw them from space to fix them upon a minute atom; and the eye adapts itself instantly to each of these uses. By means of a circle of delicate fibres, so small that till lately their existence and uses were unknown, — the ciliary muscle, — the convexity of the crystalline lens can be increased, and its focal power varied; and thus, without conscious effort, .the eye may contemplate the glories of the firmament, or catch the first flitting expression of an infant's love, or explore the mysteries of microscopic existences.