The organs of vision : their structure and functions / by G.J. Witkowski ; tr. by Henry Power.

  • Gustave-Joseph Witkowski
Date:
[1878?]
Catalogue details

Licence: Public Domain Mark

Credit: The organs of vision : their structure and functions / by G.J. Witkowski ; tr. by Henry Power. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    series of membranes enclosed one within the other, which serve as envelopes to fluids of greater or less density, known as the media of the eye. The membranes are three in number, and [are named respec- tively, proceeding from without inwards : 1. The sderotic (55), and the cornea (120), ^^^lich are fibrous membranes acting as protective envelopes. 2. The choroid (123), and the iris (130), which are muscular and vascular membranes presiding over the nutrition and the accommodation of the globe of the eye. 3. The retina (11:3), which is the nervous membrane that re- ceives the impression of light. The media of the eye are also three in number, and are named respectively, from before backwards, the aqiieous humour, the crystalline lens, and the vitreous humour. (A.) Membranes of the Eye. 1. Sclerotic. This is the most, external of the membranes in- vesting the eye, and is at once the thickest and the strongest, as is indicated by its etymology, the name being derived from the Greek ivord <rzXf]dg, hard. The sclerotic is inextensible, and its defective elasticity explains the intolerable pain that is experienced when the'[ ciliary nerves (116) are compressed by intra-orbital effusion. The pain can be relieved by puncturing the sclerotic, or, still better, by removing part of the iris (131), an operation that is termed iridectomy. The colour of the sclerotic is of a dull white, but in infants it is more transparent; and thus permitting the subjacent choroid (123) to be seen through, it presents a bluish tint. This peculiarity is still more marked in those who are phthisical and anaemic. In jaundice the sclerotic, like the tissues and humours of the body generally, assumes a yellow hue. Collyria containing nitrate of silver will stain the sclerotic of a more or less intense black. Dr. Larcher has pointed out that the appearance of a livid spot on the sclerotic some hours after supposed death is a certain sign that death has really occurred. My own observations have demon- strated that this spot is to be regarded as the first apparent sign of putrefaction, but that it is only under certain conditions that it be- comes manifest. Thus, I have never observed its occurrence'when the eyelids have remained hermetically sealed ; whilst, on the con- trary, it is rarely absent when they have remained open and exposed to the light. The discoloration takes the form of the palpebral fissure, and varies in size with the extent to which the lids are separated. The cause of its formation is unquestionably