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In illustrating these different modes of advancing medical knowledge, we shall see, in each case, the wisdom of the injunction, which points out the "way of experiment."
Of the inductive and physiological study we have not far to seek for an illustration, for we have a very model in the investigations by which our own Harvey discovered and demonstrated the Circulation of the Blood. Let us consider what were the paths he trod in searching out this great secret of Nature, what guides he had, and how he was equipped for the enterprise.
The discovery has sometimes been spoken of as if it had been a simple inference from that of the valves in the veins made by Fabricius; as if it were only one of those
Catch me who can, and make the catcher crown'd."
Even if it were so, the honour would be no small one. To seize the unknown truth in the known fact is the very essence of scientific discovery. But the inference supposed could not have been simple or easy. Consider the length of time that intervened between the two discoveries. Fabricius discovered the valves of the veins in
