In a previous communication,1the reaction time of the normal pupil was established by cinematographic means. Briefly, it was found that when light is flashed on a normal eye that is accommodated for the dark, there occurs a latent period of 0.1875 second before the pupil begins to contract. Then there follows a rapid primary contraction for 0.4365 second at the rate of 5.48 mm. per second. This is succeeded by a secondary contraction of 0.3125 second at the slower rate of 1.34 mm. per second. These experiments were conducted on normal young persons, an 8 ampere arc light being used for illumination, and the pupillary play being recorded by a spring-driven cinematographic camera of constant speed. The films thus obtained were projected on a screen, frame by frame, and the pupillary diameters measured in the projected pictures. The relationship to the corneal diameter, which was measured in the