His [Alfred Gruenfeld's] tours de force, in the way of mere execution, were no less surprising than his versatility with respect to touch and tone-production. I have, for instance, repeatedly heard him play Chopin's well-known waltz in D flat — the right-hand part, of course — in octaves at full speed, without omitting a single ornament. Every pianist will admit that this, in its way, is an incomparable feat. With such marvels of dexterity, however, he was never weary of regaling his friends, and would play to them all day and all night long, if they wished it, without exhibiting the least sign of fatigue, I never, before or since, encountered such an indefatigable performer.