The AA. study the unist and plurist concepts of hereditary nervous diseases and conclude defending Marinesco and co-worker's theory, which classifies all the above referred affections into a single group. The different doctrins about the pathogenesis of the spino-cerebe-lar degeneration are discussed, including Rabinowitsch's hypothesis, which admits the primary and initial lesion in the embryonic mesoder-mic layer, with the consequent vulneration of the central nervous system to the pathogenic agents. The AA. report the case of two sisters, both with typical cerebellar heredo-ataxia.
