So far as these records go, they entirely confirm the results of other investigators as to the direction and the reversal of the nystagmus. In each of the cases the after-image moved with the slow eye-movements, reversing its direction with these slow movements, while the visual field whenever it was observed (the eyes were kept closed during the rotation) moved in the opposite direction to that of the after-image and the slow eye-movement. It is well known that after-images move _with_ every involuntary eye-movement, and although they disappear during voluntary eye-jumps,[21] they reappear at the end of the jump in a position that is related to the new fixation-point exactly as the old position was to the former fixation-point. These after-images, then, are seen during the slow eye-movements whose direction they follow; but are not seen during the quick movements, when they must naturally move in the direction of these quick movements. And aside from this it is possible to observe introspectively that the after-image disappears at that side of the visual field toward which the slow eye-movements tend, and is for a moment invisible before it reappears on the other side of the field. As was shown above, the visual field always moves opposite to the direction of the slow eye-movements, as must of course be the case if there is no inhibition of vision during these movements. The simultaneous appearance of the after-image moving with, and the rest of the visual field moving contrary to, the direction of the slow eye-movements, with a uniform absence of the converse phenomena, seems to prove that vision is unimpaired during these slow movements, while it is completely inhibited during the rapid phases of the nystagmus. Purkinje himself[22] called the slower phases "involuntary and unconscious," meaning by "unconscious" not that the visual field was not seen (for it just then is seen), but that the movement of the eyeball during the slow phases was not felt. I have observed, with the confirmation of several subjects, that _this_ movement can also not voluntarily be inhibited; whereas the swift movement is so far voluntary that it can be inhibited at pleasure. It is possible, that is, to fix the eyes on that side of the field toward which the slow movements are directed, but not on any point at the other side of the field. The slow movements, then, during which vision is possible, are purely reflex. These slow movements, purely reflex and yielding clear vision, with the rapid movements, partly under voluntary control and attended by an inhibition of vision, present a parallelism, that may be not without significance, to the "pursuit" eye-movements (Dodge's "second type"), that are likewise relatively slow, are reflex, and yield remarkably clear vision, and the ordinary voluntary eye-jumps (Dodge's "first type"), that are relatively rapid, and are, like the rapid nystagmiform movements, attended by a central inhibition of vision. FOOTNOTES: