“…Because we have believed, as O'Leary said, we have stopped thinking, though it is to be feared that some of us who have disbelieved may have stopped thinking too, as Lobitz recently so engagingly pointed out. 1 Most doctors today are committed by our heritage from the microbiologic period in medicine to a belief, in general, in a single pathogenic mechanism for a single disease. None of us can remember the day\p=m-\it was a century ago-when almost all reasonable physicians supposed that most diseases, if not all, had various causes in various pa¬ tients.…”