When the abscess is of considerable size, both _third_ and _sixth_ nerves may be involved. For instance, the third nerve, emerging from the brain at the anterior border of the pons, and passing along the inner border of the temporo-sphenoidal lobe, is liable to irritation or pressure paralysis. In the former case, the pupil on the affected side will be contracted, in the latter instance dilated. When _ipso-lateral_ third nerve paralysis coexists with paralysis of the opposite face and upper extremity, a condition of crossed paralysis results. When the sixth nerve is involved the external rectus on the side of the lesion is paralyzed with resultant internal squint. Conjugate deviation of the eyes towards the side opposite to the lesion and secondary lateral nystagmus have both been observed. Further assistance in the localization may be obtained by careful observation as to the position of the headache, by palpation and percussion of the skull, and by a comparison of the intensity of optic neuritis in the two disks. (_b_) =Cerebellar abscess.= Many of the symptoms previously described when dealing with brain abscess in general are intensified when the focus of suppuration is situated in the confined space beneath the tentorium cerebelli. Thus, headache is exceptionally severe and more or less localized to the occipital and cerebellar regions. Again, optic neuritis may develop rapidly and reach a high grade of intensity, vomiting is early in onset and of frequent occurrence, whilst certain other symptoms dependent on the increased intracranial pressure--slowing of the pulse, alterations in respiratory rhythm--are correspondingly accentuated. The more typical _localizing_ symptoms are as follows:-- _Vertigo_ is a prominent symptom, most evident on sudden alteration of position on the part of the patient. He complains, for instance, of great giddiness on sitting up in bed. The sensation of movement may be of self or of objects. [Illustration: FIG. 77. A CEREBELLAR ABSCESS.] When standing, he tends, when unsupported, to fall or lurch in some particular direction, more commonly, in my experience, towards that side on which the abscess is situated. On this point, however, there is some difference of opinion and, by itself, it cannot be accepted as having any great localizing value. In some rare cases Dana’s symptom may be noticed--a sudden unexpected attack of vertigo, roaring in the head, relaxation of limbs, and falling to the ground in an unconscious state. This symptom is said to be almost pathognomonic of an abscess (or tumour) situated in the region of the cerebello-pontine angle.