If one tries to determine the site of a lesion that produces nystagmus, the direction of the nystagmus is of great importance. The appearance of vertical nystagmus in particular is significant, since it usually indicates (apart from rare lesions of the vertical canals) a disease of the central nervous system (Leidler1). Clinical experiences (Marburg2) indicate that vertical nystagmus usually is caused by a lesion in the cranial part of the vestibular nuclei, and the experiments of Leidler3 on rabbits also point to the importance of the cranial part of the vestibular nuclei.
Our attention was directed to this problem in a former series of experiments in which we produced bilateral lesions of the vestibular nuclei in a study of the effects of such lesions on the production of optokinetic nystagmus.4 We noticed that in some of the cats operated on vertical or mixed vertical and rotatory