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. Both are therefore strictly questions of quality. And the two are sufficient to identify appearance 5, for if no red or orange is visible, images 1, 2, and 3 are excluded; and if no green lies to the right or left of the yellow band, image 4 is excluded. Thus if one is to make the somewhat superficial distinction between qualitative and quantitative judgments, the judgments here required are qualitative. Moreover, the subjects make these judgments unhesitatingly. Finally, the method of making judgments on after-images is not new in psychology. Lamansky's well-known determination of the rate of eye-movements[22] depends on the possibility of counting accurately the number of dots in a row of after-images. A very much bolder assumption is made by Guillery[23] in another measurement of the rate of eye-movements. A trapezoidal image was generated on the moving retina, and the after-image of this was projected on to a plane bearing a scale of lines inclining at various angles. On this the degree of inclination of one side of the after-image was read off, and thence the speed of the eye-movement was calculated. In spite of the boldness of this method, a careful reading of Guillery's first article cited above will leave no doubt as to its reliability, and the accuracy of discrimination possible on these after-images. [22] Lamansky, S., (Pflüger's) Archiv f. d. gesammte Physiologie, 1869, II., S. 418. [23] Guillery, (Pflüger's) Archiv f. d. ges. Physiologie, 1898, LXXI., S. 607; and 1898, LXXIII., S. 87. As to judgments on the color and color-phases of after-images, there is ample precedent in the researches of von Helmholtz, Hering, Hess, von Kries, Hamaker, and Munk. It is therefore justifiable to assume the possibility of making accurately the four simple judgments of shape and color described above, which are essential to the two proofs of anæsthesia. V. SUMMARY AND COROLLARIES OF THE EXPERIMENTS, AND A PARTIAL, PHYSIOLOGICAL INTERPRETATION OF THE CENTRAL ANÆSTHESIA.