=Mental disturbances.= In the earlier stages of tumour development the patient is irritable, depressed, or apathetic, shows his objection to his fellow mortals on all possible occasions, is unable to concentrate his attention or exhibits impairment of memory. As has rather quaintly been observed, he appears in every sense to ‘have a weight on his mind.’ Inquiry amongst relatives will show that he has ‘changed in every way’, or ‘is not the same man’. Mental changes vary according to the site and size of the tumour. For example, it has been stated that a general air of elation or exhilaration (Witzelsucht) may be regarded as almost diagnostic of tumours situated in the anterior part of the frontal lobe. As the tumour increases in size, somnolence becomes the marked feature, progressing on to stupor and coma. In rare cases, mania may develop. =Optic neuritis.= Optic neuritis must be regarded as one of the most constant and valuable symptoms in the diagnosis of intracranial tumour formation. The degree to which it progresses depends more on the site of the tumour than on its size. In general, it may be stated that it is most constantly associated with tumours of the temporo-sphenoidal and cerebellar regions, less common in frontal tumour formation, still less frequent in post-central tumours, and perhaps least common in tumours of the pons. In this last-mentioned case optic neuritis is always late in development, and not infrequently absent throughout the whole stage of the illness. Primary optic atrophy only occurs when the tumour exerts direct compression on the optic chiasma and tracts--for example, pituitary tumours. Paton,[42] from a series of 252 cases treated at the National Hospital, of which 202 were accurately diagnosed, found that optic neuritis or atrophy was present in 81·2 per cent. cases. The fundus change, though usually bilateral, may be confined to the ipso- or contra-lateral side. Considerable discussion has taken place as to the localizing value of unilateral disk changes. For instance, it has been stated that a unilateral neuritis indicates that the tumour is situated on that side of the brain, and that when disk changes are bilateral the side which evidences the higher grade of inflammation is the side on which operation should be conducted. In the light, however, of the most recent research it would appear that unilateral symptoms are not to be relied on in establishing the localization of the tumour. Gowers[43] lays stress on the statement that with strictly unilateral neuritis one should always suspect a general rather than a local exciting cause.