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guess the form and the delineations of the expanded leaf or flower from the mere outline of the bud, and guesses in science too often mislead and hinder the advance of truth. Direct experiments have led to the establishment of scientific facts, but mere reasoning on hypothetical data has been the greatest hindrance to the progress of science. The history of physiological science illustrates these statements, and in no branch of physiology is it more remarkable than in that of the circulation. In the discovery of the circulation of the blood the process was a gradual one; the steps were often uncertain, and too fre- quently were retrograde in character. The story of the great discovery of Harvey has been often told, and my predecessors have traced it out step by step with accuracy and with skill. I do not wish to go over the same ground, for it has been better done than I could possibly expect to be able to do it.
Fragments of truth as to the function of the heart, and the nature of the circu- lation are found in the writings of Plato,
