24. 18 May 1971 [ES]
As to the deterioration: I came across a reference by Thomas Mann the other day in a letter of June 1943 saying to a casual correspondent that he tought that Schumann's creative decline was attributable not so much to his marriage as to his progressive paralysis - though to be sre one could not very well mention that! This is the earliest non-medical reference I've ever seen. It's presumably the first seed of what eventually grew into Dr Faustus, all about the incarnate German composer who used cipher and had syphilis.