He felt well acquainted with the essence of evaluating experiments—as he said, “understanding when a thing is really known and when it is not really known.” He could see at once how the centrifuge worked and how ultraviolet absorption would show how much DNA remained in a test tube. Biology was messier—things grew and wiggled, and he found it difficult to repeat experiments as exactly as he wished. He focused on a particular mutation of the T4 virus called rII.
