Demyelination is often secondary to an infectious, ischemic, metabolic, or hereditary disorder or to a toxin (eg, alcohol, ethambutol). In primary demyelinating disorders, cause is unknown, but an autoimmune mechanism is suspected because the disorder sometimes follows a viral infection or viral vaccination.
For other uses, see Realm (disambiguation). A realm /ËrÉlm/ is a community or territory over which a sovereign rules; it is commonly used to describe a kingdom or other monarchical or dynastic state. The Old French word reaume, modern French royaume, was the word first adopted in English; the fixed modern spelling does not appear until the beginning of the 17th century.
Geography (from Greek Î³ÎµÏÎ³ÏÎ±ÏÎ¯Î±, geographia, literally earth description) is a field of science devoted to the study of the lands, the features, the inhabitants, and the phenomena of Earth. The first person to use the word Î³ÎµÏÎ³ÏÎ±ÏÎ¯Î± was Eratosthenes (276â194 BC). Geography is an all-encompassing discipline that seeks an understanding of the Earth and its human and natural complexitiesânot merely where objects are, but how they have changed and come to be. It is often defined in terms of the two branches of human geography and physical geography.