It is the habit of the elderly to reminisce and an eponymous lecture is a proper occasion for commemoration, but I take it there is nothing to forbid one near the end of his professional life from looking out over the promised land.It was my good fortune to know Mackenzie Davidson. He was the doyen of radiologists, but that did not prevent young colleagues from benefiting by his advice, for he was eminently approachable. He combined eagerness with imperturbable dignity; speculation with cautious acceptance; inexhaustible curiosity with skill in the practical application of knowledge; and he set a standard for radiologists which, followed by others, has secured a position of equality with that of all who profess specialist status: status as clinician; status as man of science; status as man of wisdom in the counsels of the medical profession.For most medical men the six or seven war years were too fully occupied to leave time for thought about such matters as the cause of cancer. When one turned again to the subject it was to find that changes had come over the scene. For one thing the attitude of the “pure scientist” towards those who work in the biological and particularly in the clinical fields had become more tolerant. We know very well thatourproblems hold many variables and many factors insusceptible of measurement, but the physicist's own field proves to involve an uncertainty principle. The position is still that irreverently described by Hilaire Belloc.