The endarteritis which occurs in syphilis is characteristic and diagnostic. This has been studied exhaustively by Heubner. The smaller vessels show an infiltration of lymphoid and plasma cells in their adventitia, as well as in the perivascular lymph spaces. The larger vessels show a great thickening of the intima which is consecutive, or, as Lambert described it, "girdling" in character. This is associated with a splitting of the membrana elastica. The proliferated intimal tissue is very susceptible to degenerative processes. Thrombosis and the formation of anemic infarctions may follow the obliteration of the vascular channels. The involvement of the larger vessels may lead to very distinctive focal symptoms. Thus, as Barker[185] has pointed out, there may be an obliterating process in the middle cerebral with hemiplegia and aphasia, invasion of the basilar artery with pontile or bulbar symptoms, or an involvement of the posterior cerebral may lead to hemianesthesia or hemianopsia, while an affection of the vertebral may show a unilateral bulbar paralysis with hemianesthesia of the same side and a hemiplegia of the opposite side. The extensive involvements of the base are usually meningeal, with gumma formation and with a secondary endarteritis in addition. Large solitary gummata may, moreover, occur practically anywhere in the brain, although they are somewhat unusual. On microscopical examination they show a characteristic infiltration of the periphery and a caseous center. They are more likely to occur in the course of a large vessel.