Our present knowledge as to the relation of syphilis to this disease has not changed the significance of the observations made by Osler in any way. Heredity more than any other one factor undoubtedly determines the development of both senility and arteriosclerosis. "When," as Lambert[163] expresses it, "physiological involution anticipates in time or exceeds in direction, extent and severity normal senescence, the various senile and arteriosclerotic disorders are the result." It is as a rule only in the later stages of the disease when focal symptoms occur or a psychosis develops that hospital care becomes necessary. Practically any of the vessels of the brain may be involved and it frequently happens that more than one is affected either directly or indirectly. The neurological symptoms resulting depend entirely on the location and extent of the lesion. Lambert[164] has made the following excellent anatomical classification of the more common arteriosclerotic processes:— I. Incipient type. II. Focal types. (a) Trunk disorders. 1. Basilar-carotids. (b) Branch disorders. 1. Inferior cerebellar. 2. Superior cerebellar. 3. Posterior cerebral. 4. Middle cerebral. 5. Anterior cerebral. (c) Twig disorders. 1. Medullary. 2. Cortical. Some reference should be made, perhaps, to the focal symptoms resulting from more or less sharply circumscribed lesions which are productive of certain fairly well known complexes, whether due to arteriosclerotic softenings, hemorrhages, or growths. These have been concisely summarized by Barker[165] somewhat as follows:— Frontal Lobes—Lesions of the left inferior frontal in righthanded persons cause motor aphasia. Subcortical involvements cause word dumbness. Disturbances in the anterior part of the frontal region are sometimes associated with the Witzelsucht of the German writers—a tendency towards joking and witticisms. Central and Paracentral Lobules—Contralateral sensory, motor symptoms or a combination of the two. Monoplegias, anesthesias and Jacksonian epilepsies are characteristic. Contralateral tactile agnosia and apraxia occur, especially in lesions of the left hemisphere. An involvement of the left side may also cause a homolateral apraxia, dyspraxia or a tactile agnosia. Parietal Lobes—Lesions in the anterior part cause contralateral somesthetic disturbances, tactile agnosia or apraxia. Involvement of the left angular gyrus may cause optic aphasia or alexia; if deep enough, hemianopsia results. The voluntary movement of the eye may be interfered with.