Pg63–64:

One morning in 1946_78ya in Los Angeles, Stanislaw Ulam, a newly appointed professor at the University of Southern California, awoke to find himself unable to speak. A few hours later he underwent dangerous surgery after the diagnosis of encephalitis. His skull was sawed open and his brain tissue was sprayed with antibiotics. After a short convalescence he managed to recover apparently unscathed.

In time, however, some changes in his personality became obvious to those who knew him. Paul Stein, one of his collaborators at the Los Alamos Laboratory (where Stan Ulam worked most of his life), remarked that while Stan had been a meticulous dresser before his operation, a dandy of sorts, afterwards he became visibly sloppy in the details of his attire even though he would still carefully and expensively select every item of clothing he wore.

Soon after I met him in 1963_61ya, several years after the event, I could not help noticing that his trains of thought were not those of a normal person, even a mathematician. In his conversation he was livelier and wittier than anyone I had ever met; and his ideas, which he spouted out at odd intervals, were fascinating beyond anything I have witnessed before or since. However, he seemed to studiously avoid going into any details. He would dwell on any subject no longer than a few minutes, then impatiently move on to something entirely unrelated.

Out of curiosity, I asked John Oxtoby, Stan’s collaborator in the thirties (and, like Stan, a former Junior Fellow at Harvard) about their working habits before his operation. Surprisingly, Oxtoby described how at Harvard they would sit for hours on end, day after day, in front of the blackboard. From the time I met him, Stan never did anything of the sort. He would perform a calculation (even the simplest) only when he had absolutely no other way out. I remember watching him at the blackboard, trying to solve a quadratic equation. He furrowed his brow in rapt absorption while scribbling formulas in his tiny handwriting. When he finally got the answer, he turned around and said with relief: “I feel I have done my work for the day.”

The Germans have aptly called Sitzfleisch the ability to spend endless hours at a desk doing gruesome work. Sitzfleisch is considered by mathematicians to be a better gauge of success than any of the attractive definitions of talent with which psychologists regale us from time to time. Stan Ulam, however, was able to get by without any Sitzfleisch whatsoever. After his bout with encephalitis, he came to lean on his unimpaired imagination for his ideas, and on the Sitzfleisch of others for technical support. The beauty of his insights and the promise of his proposals kept him amply supplied with young collaborators, willing to lend (and risking the waste of) their time.

The recollections of Eugene P. Wigner as told to Andrew Szanton, Wigner 1992_32ya, pg109–110:

Does it seem odd for a mathematician like Hilbert to take a young physicist for an assistant? Well, Hilbert needed no help in mathematics. But his work embraced physics, too, and I hoped to help Hilbert somewhat with physics.

So I was quite excited to reach Göttingen in 1927_97ya. I was quickly and deeply disappointed. I found Hilbert painfully withdrawn. He had contracted pernicious anemia in 1925_99ya and was no longer an active thinker. The worst symptoms of pernicious anemia are not immediately obvious, and Hilbert’s case had not yet been diagnosed. But we knew already that something was quite wrong. Hilbert was only living halfway. His enormous fatigue was plain. And the correct diagnosis was not encouraging when it came. Pernicious anemia was then not considered curable.

So Hilbert suddenly seemed quite old. He was only about 65, which seems rather young to me now. But life no longer much interested him. I knew very well that old age comes eventually to everyone who survives his stay on this earth. For some people, it is a time of ripe reflection, and I had often envied old men their position. But Hilbert had aged with awful speed, and the prematurity of his decline took the glow from it. His breadth of interest was nearly gone and with it the engaging manner that had earned him so many disciples.

Hilbert eventually got medical treatment for his anemia and managed to live until 1943_81ya. But he was hardly a scientist after 1925_99ya, and certainly not a Hilbert. I once explained some new theorem to him. As soon as he saw that its use was limited, he said, “Ah, then one doesn’t really have to learn this one.” It was painfully dear that he did not want to learn it.

…I had come to Göttingen to be Hilbert’s assistant, but he wanted no assistance. We can all get old by ourselves.