In the 30's, syphilis was considered an incurable disease and was also the major cause for dementia, making people violent, paranoid and uncontrolable. They often ended up in asylums and there was not much left to do for those poor souls.
But the Austrian doctor Julius Wagner von Jauregg noticed that when these patients contracted diseases that caused episodes of high fever and convulsions, the madness disappeared. So, he decided to inject the blood of a soldier contaminated with malaria in 9 patients with chronic paresis (an incomplete pralisis or decrease of motricity in one or more parts of the body, due to lesions in the nervous centers, or in the motor pathways or in the peripheric nervous system - which can be caused by syphilis). Four of those patients recovered from dementia, and two other also presented improvements. Those results gave Dr. von Jauregg the Nobel Prize in 1927. However, this treatment was very dangerous - obviously, because you got better from madness, but then you had malaria. Great, huh?! - and ceased to be used in the 60's, when antibiotics and proper medicines for mental problems were discovered.