The attitude of the true scientist towards the real limits of human understanding was unforgettably impressed on me in early youth by the obviously unpremeditated words of a great biologist; Alfred Kuhn finished a lecture to the Austrian Academy of Science with Goethe 's words, "It is the greatest joy of the man of thought to have explored the explorable and then calmly to revere the inexplorable." After the last word he hesitated, raised his hand in repudiation and cried, above the applause, "No, not calmly, gentlemen; not calmly!