Mogens Schou, a Danish psychiatrist who, more than anyone, is responsible for the introduction of lithium as a treatment for manic-depressive illness, and I had decided to skip a day’s sessions of the American Psychiatric Association’s annual meeting and take advantage of being in New Orleans. The best way to do this, we decided, was to take a boat ride down the Mississippi River. It was a gorgeous day, and, after having discussed a wide variety of topics, Mogens turned to me and asked me point-blank, Why are you really studying mood disorders? I must have looked as taken aback and uncomfortable as I felt, because, changing tack, he said, “Well, why don’t I tell you why I study mood disorders?”