What is the cause of the symptoms in this group of cases? Possibly in some cases the symptoms are caused by a non-malignant tumor (or tuberculous mass) which ceases to extend and becomes quiescent and encapsuled. One of us has recorded a case in which symptoms of cerebral tumor (including Jacksonian epilepsy and hemiplegia) gradually subsided and temporary recovery ensued; but three years later symptoms of cerebellar tumor developed and death occurred. The necropsy revealed a recent large tuberculous mass in the cerebellum and an old capsuled tuberculous mass just beneath the motor cortex in the right cerebral hemisphere. The latter had evidently been the cause of the early cerebral symptoms from which the patient had recovered. An instructive case has been recorded by Dr. T. K. Monro of Glasgow. The patient, at the age of sixteen years, suffered from severe headache with failure of vision which passed on to complete blindness. For thirty-three years he was an inmate of a blind asylum, ophthalmoscopic examination showing double optic atrophy. He died at the age of sixty-three years, from cancer of the stomach, and the post-mortem examination also revealed a large myxomatous tumor in the left half of the cerebellum. In all probability the early cerebral symptoms had been associated with optic neuritis which had passed on to optic atrophy and the cause had been the myxoma in the cerebellum which had remained quiescent for forty-six years. In some cases of double optic neuritis with headache and general cerebral symptoms, when recovery occurs the cause is probably distention of the ventricles of the brain with fluid—serous meningitis of the ventricles (Quincke). This condition was present at the necropsy, and no tumor growth could be found in two out of the one hundred cases tabulated. It is probable that a number of the cases in which a diagnosis of cerebral tumor has been made, but in which recovery has occurred, have been due to this condition—serous meningitis of the ventricles. Probably the two cases in Group IX. and possibly some of the cases in Group II., in which death did not occur for several years after the onset of symptoms, were of this nature. Other cases which recover may be due to a basal meningitis. The table given above is instructive both as regards the diagnosis and prognosis in cases of double optic neuritis with headache. It shows the necessity for careful examination before giving either a diagnosis or prognosis, and the clinical group of cases No. X. ought always to be borne in mind whenever the diagnosis is obscure and localizing symptoms are absent.