te treatment than drugs. While one
could measure with great accuracy the dosages of such drugs as emetics,
diuretics, and purgatives, Galen argued that their action on the body was
directed by chance and could not easily be observed by the physician.[11]
However, the effects of bloodletting were readily observed. One could note
the change in the color of the blood removed, the complexion of the
patient, and the point at which the patient was about to become
unconscious, and know precisely when to stop the bleeding.

Galen discussed in great detail the selection of veins to open and the
number of times blood might be withdrawn.[12] In choosing the vein to
open, its location in respect to the disease was important. Galen
recommended that bleeding be done from a blood vessel on the same side of
the body as the disease. For example, he explained that blood from the
right elbow be removed to stop a nosebleed from the right nostril.[13]
Celsus had argued for withdrawing blood near the site of the disease for
"bloodletting draws blood out of the nearest place first, and thereupon
blood from more distant parts follows so long as the letting out of blood
is continued."[14]

Controversy over the location of the veins to be opened erupted in the
sixteenth century. Many publications appeared arguing the positive and
negative aspects of bleeding from a vein on the same side
(derivative--from the Latin _derivatio_ from the verb _derivare_, "to draw
away," "to divert") or the opposite side (revulsion--from the Latin
_revulsio_, "drawing in a contrary direction") of the disordered part of
the body. This debate mirrored a broader struggle over whether to practice
medicine on principles growing out of medieval medical views or out of
classical Greek doctrines that had recently been revived and brought into
prominence. The medieval practice was based on the Moslem medical writers
who emphasized revulsion (bleeding from a site located as far from the
ailment as possible).[15] This position was attacked in 1514 by Pierre
Brissot (1478-1522), a Paris physician, who stressed the importance of
bleeding near the locus of the disease (derivative bleeding). He was
declared a medical heretic by the Paris Faculty of Medicine and derivative
bleeding was forbidden by an act of the French parliament. In 1518,
Brissot was exiled to Spain and Portugal. In 1539, the celebrated
anatomist, Andreas Vesalius, continued the controversy with his famous
_Venes