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., (Pflueger's) Archiv f. d. gesammte
Physiologie, 1869, II., S. 418.

[23] Guillery, (Pflueger'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 anaesthesia.

V. SUMMARY AND COROLLARIES OF THE EXPERIMENTS, AND A PARTIAL,
PHYSIOLOGICAL INTERPRETATION OF THE CENTRAL ANAESTHESIA.

We have now to sum up the facts given by the experiments. The fact of
central anaesthesia during voluntary movement is supported by two
experimental proofs, aside from a number of random observations which
seem to require this anaesthesia for their explanation. The first proof
is that if an image of the shape of a dumb-bell is given to the retina
during an eye-movement, and in such a way that the handle of the
image, while positively above the threshold of perception, is yet of
brief enough duration to fade completely before the end of the
movement, it then happens that both ends of the dumb-bell are seen but
the handle not at all. The fact of its having been properly given to
the retina is made certain by the presence of the now disconnected
ends.

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