The frequent and unmistakable appearance of this band of straw-yellow on a non-elongated green field without the previous phase in which the band is reddish-orange, although this latter was unmistakable when the same stimulation was given to the eye at rest, is authenticated by eight subjects. This appearance, together with that of the handleless dumb-bell, is submitted as a demonstration that during voluntary movements of the eyes, and probably of the head as well, there is a moment in which stimulations are not transmitted from the retina to the cerebral cortex, that is, a moment of central anaesthesia.  The reason for saying ’and probably of the head as well,’ is that although the phenomena described are gotten equally well from movements of the head, yet it is not perfectly certain that when the head moves the eyes do not also move slightly within the head, even when the attempt is made to keep them fixed.

Most of the criticisms which apply to this last experiment apply to that with the dumb-bell and have already been answered.  There is one however which, while applying to that other, more particularly applies here.  It would be, that these after-images are too brief and indistinct to be carefully observed, so that judgments as to their shape, size, and color are not valid evidence.  This is a perfectly sensible criticism, and a person thoroughly convinced of its force should repeat the experiments and decide for himself what reliance he will place on the judgments he is able to make.  The writer and those of the subjects who are most trained in optical experiments find the judgments so simple and easily made as not to be open to doubt.

In the first place, it should be remembered that only those cases are counted in which the movement was so timed that the image was seen in direct vision, that is, was given on or very near the fovea.  In such cases a nice discrimination of the shape and color of the images is easily possible.

Secondly, the judgments are in no case quantitative, that is, they in no case depend on an estimate of the absolute size of any part of the image.  At most the proportions are estimated.  In the case of the dumb-bell the question is, Has the figure a handle?  The other question, Are the end-circles horizontally elongated? has not to be answered with mathematical accuracy.  It is enough if the end-circles are approximately round, or indeed are narrower than 9 cm. horizontally, for at even that low degree of concentration the handle was still visible to the resting eye.  Again, in the experiment with the color-phases, only two questions are essential to identify the appearance 5:  Does the horizontal yellow band extend quite to both edges of the image? and, Is there certainly no trace of red or orange to be seen?  The first question does not require a quantitative judgment, but merely one as to whether there is any green visible to the right or left of the yellow strip.