It was just the kind of thing that the botanical professor was always doing. Like the income tax, it offered a premium to the cheat. It was a preparation under the microscope, a little glass slip, held in its place on the stage of the instrument by light steel clips, and the inscription set forth that the slip was not to be moved. Each student was to go in turn to it, sketch it, write in his book of answers what he considered it to be, and return to his place. Now to move such a slip is a thing one can do by a chance movement of the finger, and in a fraction of a second. The professor’s reason for decreeing that the slip should not be moved depended on the fact that the object he wanted identified was characteristic of a certain tree stem. In the position in which it was placed it was a difficult thing to recognise, but once the slip was moved so as to bring other parts of the preparation into view, its nature was obvious enough. Hill came to this, flushed from a contest with staining reagents, sat down on the little stool before the microscope, turned the mirror to get the best light, and then out of sheer habit shifted the slip. At once he remembered the prohibition, and with an almost continuous motion of his hands, moved it back, and sat paralysed with astonishment at his action. Then slowly he turned his head. The professor was out of the room, the demonstrator sat aloft on his impromptu rostrum, reading the “Q. Jour. Mi. Sci.,” the rest of the examinees were busy and with their backs to him. Should he own up to the accident now? He knew quite clearly what the thing was. It was a lenticel, a characteristic preparation from the elder-tree. His eye roved over his intent fellow-students and Wedderburn suddenly glanced over his shoulder at him with a queer expression in his eyes. The mental excitement that had kept Hill at an abnormal pitch of vigour these two days gave way to a curious nervous tension. His book of answers was beside him. He did not write down what the thing was, but with one eye at the microscope he began making a hasty sketch of it. His mind was full of this grotesque puzzle in ethics that had suddenly been sprung upon him. Should he identify it? Or should he leave this question unanswered? In that case Wedderburn would probably come out first in the botanical list. How could he tell now whether he might not have identified the thing without shifting it? It was possible that Wedderburn had failed to recognise it, of course. Suppose Wedderburn, too, had shifted the slide? He looked up at the clock. There were fifteen minutes in which to make up his mind. He gathered up his book of answers and the coloured pencils he used in illustrating his replies, and walked back to his seat.