The disappearance of after-images during eye-movements is mentioned by Fick and Gürber,[4] who seek to explain the phenomenon by ascribing it to a momentary period of recovery which the retina perhaps undergoes, and which would for the moment prevent further stimulations from being transmitted to the optic nerve. Exner observes that this explanation would not, however, apply to the disappearance of the vessel-figure, the circulation phenomenon, the foveal figure, the polarization-sheaf of Haidinger, Maxwell's spot, or the ring of Löwe; for these phenomena disappear in a similar manner during movement. Exner offers another and a highly suggestive explanation. He says of the phenomenon (_op. citat._, S. 47), "This is obviously related to the following fact, that objective and subjective impressions are not to be distinguished as such, so long as the eye is at rest, but that they are immediately distinguished if an eye-movement is executed; for then the subjective phenomena move with the eye, whereas the objective phenomena are not displaced.... This neglect of the subjective phenomena is effected, however, not by means of an act of will, but rather by some central mechanism which, perhaps in the manner of a reflex inhibition, withholds the stimulation in question from consciousness, without our assistance and indeed without our knowledge." The suggestion of a central mechanism which brings about a reflex inhibition is the significant point. [4] Fick, Eug., and Gürber, A., _Berichte d. ophthalmologischen Gesellschaft in Heidelberg_, 1889. It is furthermore worth noting that movements of the eyelid and changes in the accommodation also cause the after-images to disappear (Fick and Gürber), whereas artificial displacement of the eye, as by means of pressure from the finger, does not interfere with the images (Exner). Another motive for suspecting anæsthesia during eye-movement is found by Dodge,[5] in the fact that, "One may watch one's eyes as closely as possible, even with the aid of a concave reflector, whether one looks from one eye to the other, or from some more distant object to one's own eyes, the eyes may be seen now in one position and now in another, but never in motion." This phenomenon was described by Graefe,[6] who believed it was to be explained in the same way as the illusion which one experiences in a railway coach when another train is moving parallel with the coach in which one sits, in the same direction and at the same speed. The second train, of course, appears motionless. [5] Dodge, Raymond, PSYCHOLOGICAL REVIEW, 1900, VII., p. 456. [6] Graefe, A., _Archiv f. Ophthalmologie_, 1895, XLI., 3, S. 136.