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.
(b) Branch disorders.
1. Inferior cerebellar.
2. Superior cerebellar.
3. Posterior cerebral.
4. Middle cerebral.