P athological S tudies O n E ncephalopathia F rom U nknown C ause in M inamata D istrict O f K umamoto P refecture (T he S o ‐ called M inamata ‐ disease) in J apan

A sporadic outbreak of encephalopathia from unknown causes was experienced at the farming and fishing area facing the Bay of Minamata (1×2.5 km), having about ten thousands population, through the end of 1953 up to 1956. Seventeen out of all fifty‐six patients died during the period. The disease was noticed throughout a year, but the‐incidence was relatively more numerous from spring to autumn. The clinical symptoms demonstrated numbness around the mouth and of fingers in the beginning stage, but with no fever to the end. And then ataxia, hypertonic staggering gait, tremors of fingers, impairment of speech, difficulty of hearing, and restriction of the visual field were seen in some of these patients. In a severe case, the disturbance of the involuntary motion such as intention tremor, blindness, choreiform movement, athetosis and ballismus were recognized. Furthermore, dysphagia, muscular rigidity or hypotonia of muscles followed. In the terminal case, the disturbance of the coordination of feeling with condition leading to impaired consciousness was observed, and finally the patients fell into cachexy and died of pneumonia.