The output in book form of other authorities followed rapidly, and the manifest discrepancies between such teachers as Celsus, Hippocrates, Galen, and Pliny heightened still more the growing spirit of criticism.
These doubts resulted in great controversies as to the proper treatment of certain diseases, some physicians following Hippocrates, others Galen or Celsus, still others the Arabian masters.

One of the most bitter of these contests was over the question of "revulsion," and "derivation"-- that is, whether in cases of pleurisy treated by bleeding, the venesection should be made at a point distant from the seat of the disease, as held by the "revulsionists," or at a point nearer and on the same side of the body, as practised by the "derivationists." That any great point for discussion could be raised in the fifteenth or sixteenth centuries on so simple a matter as it seems to-day shows how necessary to the progress of medicine was the discovery of the circulation of the blood made by Harvey two centuries later.

After Harvey's discovery no such discussion could have been possible, because this discovery made it evident that as far as the general effect upon the circulation is concerned, it made little difference whether the bleeding was done near a diseased part or remote from it.

But in the sixteenth century this question was the all-absorbing one among the doctors.

At one time the faculty of Paris condemned "derivation"; but the supporters of this method carried the war still higher, and Emperor Charles V.himself was appealed to.