OBSERVATIONS ON VISION.

529

luminous lines, branched, and somewhatconnected with each other, darting fromevery part of the field of view, towards a cen-tre a little exterior and superior to the axis ofthe eye. This centre corresponds to the in-sertion of the optic nerve, and the appear-ance of lines is probably occasioned by thatmotion of the retina which is produced bythe sudden return of the circulating fluid, into

the veins accompanying the ramifications ofthe arteria centralis, after having been de-tained by the pressure which is now inter-mitted. As such an obstruction and such areadmission must require particular circum-stances, in order to be effected in a sensibledegree, it may naturally be supposed thatthis experiment will not always easily suc-ceed.

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