2. FOCAL LESIONS OF THE CEREBELLUM.—(_a_) Lesions strictly limited to one lateral lobe or hemisphere of this organ do not give rise to any characteristic symptoms—in some cases, indeed, to no symptoms at all. When the lesion tends basad, irritating and compressing the subjacent pons and oblongata on one side, incomplete paralysis appears in the limbs opposite the lesion, the face usually remaining normal. Occipital {91} headache, attacks of vomiting, opisthotonos, or intense subjective stiffness of the back of the neck, with neuro-retinitis, would strengthen the diagnosis. If the lesion extend laterad, so as to involve the processus ad pontem (lateral peduncle), a tendency to rotate while lying or to deviate in walking toward the side of the lesion may be added. (_b_) Lesions of the middle lobe, or vermis superior in particular, may be positively recognized during life. Besides the above-mentioned general symptoms of cerebellar and bulbar irritation and compression—viz. occipital headache, cervical stiffness, attacks of vomiting, neuro-retinitis, and atrophy of the optic nerve—there is a very characteristic, almost pathognomonic, symptom. This is cerebellar titubation, miscalled cerebellar ataxia. The patient, whose equilibrium may be perfect while lying or sitting, upon rising and attempting to walk does so somewhat like an intoxicated person: the head and body are bent forward; the arms and hands held out and moved as balancing weights; the feet are widely separated, the toes clutching the floor or carpet; the body oscillating somewhat over its base of support. There are not the wide excursions of the entire body, the zigzagging, of alcoholic intoxication, nor is there any of the stamping or jerky step of locomotor ataxia. If the patient be tested lying or sitting, it is found that neither in the hands nor in the legs is there a trace of ataxia: muscular strength and sensibility are long preserved, and the patellar reflex is exaggerated. 3. FOCAL LESIONS OF THE BASE OF THE BRAIN, either within the nervous substance or springing from the dura, and acting by irritation and pressure upon various parts of the basal aspect of the encephalic mass.