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XXVI.—On the Optical Phenomena, Nature, and Locality of Muscæ Volitantes; with Observations on the Structure of the Vitreous Humour, and on the Vision of Objects placed within the Eye

Published online by Cambridge University Press:  17 January 2013

David Brewster
David Brewster
Affiliation:
St Leonard's College, St Andrews
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Extract

Although some of the phenomena of Muscæ volitantes may be seen by persons of all ages, and with the best eyes; and though those which are more peculiarly entitled to the name are exceedingly common beyond the middle period of life; yet no account has been given of them that has even the slightest pretension to accuracy. M. De La Hire, in his Differens accidens de la Vue, describes these Muscæ as of two kinds; some permanent and fixed, which he ascribes to small drops of extravasated blood upon the retina; and others, as flying about, and changing their place, even though the eye be fixed. The first kind, he describes as like a dark spot upon a white ground; and the second, as like the knots of a deal board. Some parts of them, he says, are very clear, and surrounded with dark threads, and are accompanied with long fillets of irregular shapes, which are bright in the middle, and terminated on each side by parallel black threads.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 15 , Issue 3 , 1844 , pp. 377 - 385
Copyright
Copyright © Royal Society of Edinburgh 1844

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References

page 377 note * Smith's Optics, vol. ii. Rem. p. 5.

page 377 note † Treatise on the Eye, vol. ii. p. 74–80.

page 378 note * Practical Treatise on the Diseases of the Eye, 1830, pp. 748, 750.

page 382 note * This may be done by projecting it upon a luminous surface, and marking its apparent size; or by comparing it with the images of objects of known dimensions seen with a fine microscope.

page 383 note * The vitreous humour, when slowly dried, either by itself, or along with parts of the septa in which it may be contained, shoots into beautiful crystalline ramifications proceeding from the four angles of a quadrilateral crystal. Thin six-sided plates frequently occur, but they seem to exercise no action upon polarised light, probably on account of their thinness. The same effects were produced when the vitreous humour from a fresh eye was well washed in distilled water.

page 383 note † Medico-Chirurgical Trans., 1814, vol. v., p. 255.

page 383 note ‡ Id. Id., p. 266.

page 384 note * Lond. and Edin. Phil. Mag., 1832, vol. i., p. 172, vol. ii., p. 168.

page 384 note † Practical Treatise, &c, p. 751.

page 384 note ‡ Professor Plateau mentions that he had been led to suppose that the Muscæ had their seat in the vitreous humour rather than in the aqueous; but that he had been stopped by the difficulty of reconciling this opinion with the viscosity of the vitreous humour. As the vitreous humour is perfectly fluid within each cell, the viscosity here supposed being only apparent, no longer presents any difficulty.