166 Mr. Batchelor's Observations on a Species of Muscat 



confine my attention in the following paper, is a species of 

 inusca volitans apparently floating in the aqueous humour ; 

 which, excepting a slight notice by Mr. Ware (Medico- 

 Chirurgical Transactions, vol. v.), has been wholly overlooked, 

 or referred to other sources, by writers who have devoted 

 themselves to this branch of medicine. Mr. Ware describes 

 them as consisting of " a number of intersecting motes or 

 beams, floating before the eyes. Sometimes they appeared 

 nearly spherical, sometimes little long knotted lines, varying 

 in number, size, and opacity." This description is most ap- 

 plicable when the observer looks towards a bright cloud, or 

 gleam of sunshine through a window, immediately after waking 

 in a morning. Where the light is more feeble they give the 

 idea of dusky spots floating before the eye. Mr. Wardrop, 

 in his work on the Morbid Anatomy of the Eye, speaking of 

 floating muscae, goes so far as to say, that " if they are pro- 

 duced by any spot or opacity in the transparent humours of 

 the eye, it must be in the posterior part of the vitreous hu- 

 mour; because experiments, and the principles of optics, prove 

 that no opacity of the aqueous, crystalline, or anterior part of 

 the vitreous humour can throw a partial shadow on the re- 

 tina." The opacities of the retina are those only which 

 Mr. Wardrop has taken into consideration. 



I have tried various means of illuminating the interior of 

 the eye, in order to be enabled to examine these specks to the 

 greatest advantage. They may be seen by looking through 

 any small lens at a candle, but the optical reasons alluded to 

 by Mr. Wardrop, render it advisable to use the smallest lens 

 which can be procured ; and the light thus entering by a very 

 minute point, is obviously more likely to admit of a shadow- 

 being cast upon the retina by a small object between it and 

 that membrane. By looking through a small hole in a plate 

 of tin, I have also clearly seen a stratum of still smaller par- 

 ticles than those which appear as specks, and interfere (in a 

 trifling degree) with vision, under ordinary circumstances. 



Examining them by the above methods, these muscae are 

 found not to be opaque spots, but pellucid globules, and, 

 as nearly as I can judge of their seat, floating in the aqueous 

 humour. Though frequently suspended for a short time, they 

 seem to possess greater gravity than the medium in which they 

 exist, and when the eye is at rest sink below the line of vision. 

 From this situation they can readily be projected upwards by 

 a rapid motion of the globe of the eye in a vertical direction ; 

 and the best time for observing them is as they fall gradually 

 to the lower part of the eye, passing across the field of vision. 

 They are then seen distinctly to consist of globules, either 



detached, 



