The second proof is that, similarly, if during an eye-movement two stimulations of different colors are given to the retina, superposed and at such intensity and rate of succession as would show to the resting eye two successive phases of color (in the case taken, reddish-orange and straw-yellow), it then happens that the first phase, which runs its course and is supplanted by the second before the movement is over, is not perceived at all.  The first phase was certainly given, because the conditions of the experiment require the orange to be given if the straw-yellow is, since the straw-yellow which is seen can be produced only by the addition of green to the orange which is not seen.

These two phenomena seem inevitably to demonstrate a moment during which a process on the retina, of sufficient duration and intensity ordinarily to determine a corresponding conscious state, is nevertheless prevented from doing so.  One inclines to imagine a retraction of dendrites, which breaks the connection between the central end of the optic nerve and the occipital centers of vision.

The fact of anaesthesia demonstrated, other phenomena are now available with further information.  From the phenomena of the ’falsely localized’ images it follows that at least in voluntary eye-movements of considerable arc (30 deg. or more), the anaesthesia commences appreciably later than the movement.  The falsely localized streak is not generated before the eye moves, but is yet seen before the correctly localized streak, as is shown by the relative intensities of the two.  The anaesthesia must intervene between the two appearances.  The conjecture of Schwarz, that the fainter streak is but a second appearance of the stronger, is undoubtedly right.

We know too that the anaesthesia depends on a mechanism central of the retina, for stimulations are received during movement but not transmitted to consciousness till afterward.  This would be further shown if it should be found that movements of the head, no less than those of the eyes, condition the anaesthesia.  As before said, it is not certain that the eyes do not move slightly in the head while the head moves.  The movement of the eyes must then be very slight, and the anaesthesia correspondingly either brief or discontinuous.  Whereas, the phenomena are the same when the head moves 90 deg. as when the eyes move that amount.  It seems probable, then, that voluntary movements of the head do equally condition the anaesthesia.

We have seen, too, that in reflex eye-or head-movements no anaesthesia is so far to be demonstrated.  The closeness with which the eye follows the unexpected gyrations of a slowly waving rush-light, proves that the reflex movement is produced by a succession of brief impulses (probably from the cerebellum), each one of which carries the eye through only a very short distance.  It is an interesting question, whether there is an instant of anaesthesia for each one of these involuntary innervations—­an instant too brief to be revealed by the experimental conditions employed above.  The seeming continuity of the sensation during reflex movement would of course not argue against such successive instants of anaesthesia, since no discontinuity of vision during voluntary movement is noticeable, although a relatively long moment of anaesthesia actually intervenes.