The patient either lies listless and apathetic--mentally dulled--or exhibits general irritability, lying curled up in bed, intolerant of all interrogation and examination. More rarely, cerebral irritation progresses to actual mania, the patient tossing about in bed, muttering and delirious. Forcible restraint is often required. In the later manifest stages the patient lies comatose. =Headache.= Headache is an almost constant feature, varying greatly in intensity, but often so severe that the patient is incapacitated from all attempts at conversation and movement. Exacerbations are frequent, the sufferer crying out in his agony. The pain may be localized or diffuse. Localization of the pain to some special region is of considerable aid to the regional diagnosis of the abscess--more especially so when it is accentuated by palpation and percussion over the suspected region. =Vomiting.= Vomiting is another frequent symptom, probably dependent on stimulation of the medullary vomiting centre. It is of the so-called ‘cerebral’ type, bearing no relation to the ingestion of food and unaccompanied by previous nausea and retching. The vomited material is propelled outwards with considerable force. There appears to be some relation between the exacerbations of headache and the time at which vomiting occurs. Vomiting is most constantly observed when the abscess is subtentorial in position. =Optic neuritis.= It is exceedingly difficult to determine the frequency with which optic neuritis develops in cases of brain abscess. Much depends on the site of the abscess and the duration of its existence. Optic neuritis is seldom absent in the more chronic cases and is most constant when the purulent collection is subtentorial in position. The non-appearance of optic neuritis--even in chronic cases--does not confute a diagnosis of abscess formation. When once present, the swelling of the disk may increase rapidly. In a case of cerebellar abscess recently under my care the swelling reached 6D. in three days. Whatever the localizing value of unilateral neuritis in tumour formation (see p. 216), I am strongly of opinion that in the cases under discussion, optic neuritis, when confined to or more marked on the one side, implies that the abscess is situated on that side.