This study is limited to a survey of the glial reactions to chronic circulatory disturbances, atherosclerosis, in the central nervous system. No attempt, however, has been made to embrace all the morphologic changes in cerebral atherosclerosis, and it is unnecessary to recapitulate and to revaluate the numerous contributions on the subject of the histopathology of this disease. Instead, the reader is referred to the more important contributions in this field of Alzheimer,1 Binswanger,2 Jacobsohn,3 Oppenheim,4 Saltykow,5 Stransky,6 Rio-Hortega,7 Neuburger8 and Kodama.9 The purpose of this contribution is to chart the various glial elements in their numerical and morphologic modifications as revealed by modern tinctorial methods in a chronic progressive vascular disease. The term "chronic progressive vascular disease" in itself suggests that one is not dealing with a single sharply defined morphologic picture, but with a large series of somewhat overlapping alterations