In another paper1 we have stated that in cases of clinically unilateral simple glaucoma pupillary disturbances may generally be detected in the seemingly unaffected eye. These disturbances were found to be based on three factors: (1) modifications of the retinal receptors, (2) damage to the effector organs and (3) lesions in the central nervous system. While in the early stage of the disease the first two factors were not constant, the third factor was always present. On the basis of new experiments, we shall discuss in this paper the origin and significance of the nervous factor. Is this factor sympathetic or parasympathetic, central or peripheral ? Our studies were made both in cases of unilateral simple glaucoma, in which increase of tension has not yet occurred in the unaffected eye, and in cases of well developed glaucoma, both unilateral and bilateral. RÉSUMÉ OF PREVIOUS STUDIES Before analyzing the pupillary reactions