It is now known to be a late stage of the disease of syphilis.
General paresis most often struck people (men far more frequently than women) between twenty and forty years of age. Within a matter of months to a few years after the appearance of the first symptoms, it reduced its victims to a state of dementia and profound weakness. No treatment was known, and patients uniformly died. During the nineteenth century its prevalence came to be widely recognized. By 1877, for example, the superintendent of an asylum for men in New York reported that in his institution this disorder accounted for more than twelve percent of the admissions and more than two percent of the deaths.
While Esmarch[?] and Jessen[?] had asserted as early as 1857 that syphilis caused general paresis, progress toward the general acceptance of this idea was begun by the eminent nineteenth-century syphilographer Alfred Fournier[?] (1832-1914). In 1913 all doubt about the syphilitic nature of paresis was finally eliminated when Noguchi[?] and Moore[?] demonstrated the spirochaetes in the brains of paretics. In 1917 Julius Wagner-Jauregg[?] discovered that infecting paretic patients with malaria could halt the progression of general paresis. He won a Nobel Prize for this discovery in 1927. After World War II the use of penicillin to treat syphilis made general paresis a rarity.
But see: Tuskegee experiment