Interference with the blood supply of the spinal cord, excluding trauma, has long been recognized as the basis of sudden paraplegia. The lesion in syphilitic paraplegia is invariably thrombosis in the blood vessels, either intramedullary or extramedullary, producing thereby direct and secondary degenerative changes in the cord and giving rise to the apoplectiform symptoms. Although this view is now generally accepted, clear pathologic evidence for it is scarce. My purpose in this article, therefore, is not only to demonstrate the existence of actual thrombosed vessels and the distinctive type of softening which results directly from their occlusion, but also to show several concomitant changes in the meninges which, so far as I know, have not hitherto been described. Bastian,1 in 1882, was the first to express a definite opinion as to the cause of sudden paraplegia, known then as "acute myelitis," and maintained that "acute myelitis is in reality