172 



ORVILLE T. BAILEY 



Fig. 2. Vascular lesion in small leptomeningeal vessel near an area of myelomalacia. 

 There is heavy inflammatory cellular infiltration of the necrotic wall, but the en- 

 dothelial layer appears intact. Gallocyanin-van Gieson X250. Dosage 5,606 r Ta'*" in 

 3 months. Paraplegia at end of radiation: death 1 week later. Autopsy: myelomalacia 

 10th thoracic to 2nd lumbar segments. 



There is at least one other type of vascular occlusion in the central nervous 

 system of chronic animals. This occurs when there has been further necrosis 

 of the collagenous tissue produced in repair followed by secondary collagen- 

 ous response, eventually producing enlarged, bizarre vascular channels with 

 tiny lumina (Fig. 4) or none at all. 



These striking changes in vessel walls of chronic animals are not nearly so 

 widespread in the area of radiation as in the vasculitis of smaller vessels in 

 the acute phase. There is considerable evidence that the late vascular changes 

 are segmental. Hence more vessels may have an occluded segment at some 

 point than would be inferred from a single microscopic section or even from 

 several sections of one tissue block. 



