the pulse, opposed
venesection, while Diogenes of Appolonia (430 B.C.), who described the
vena cava with its main branches, was a proponent of the practice.
Hippocrates, to whom no specific text on bloodletting is attributed, both
approved and recommended venesection.[3]

The anatomist and physician Erasistratus (300-260 B.C.), was one of the
earliest physicians to leave a record of why he opposed venesection, the
letting of blood from a vein. Erasistratus, who practiced at the court of
the King of Syria and later at Alexandria, a celebrated center of ancient
medicine, recognized that the difficulty in estimating the amount of blood
to be withdrawn and the possibility of mistakenly cutting an artery,
tendon, or nerve might cause permanent damage or even death. Since
Erasistratus believed that only the veins carried blood while the arteries
contained air, he also feared the possibility of transferring air from the
arteries into the veins as a result of venesection. Erasistratus was led
to question how excessive venesection differed from committing murder.[4]

Through the writings of Aulus Cornelius Celsus (25 B.C.-?), the Roman
encyclopedist, and Galen (ca. A.D. 130-200) venesection was restored as a
form of orthodox medical treatment and remained so for the next fifteen
hundred years. By the time of Celsus, bloodletting had become a common
treatment. Celsus remarked in his well-known account of early medicine:
"To let blood by incising a vein is no novelty; what is novel is that
there should be scarcely any malady in which blood may not be let."[5] Yet
criticism of bloodletting continued, for when Galen went to Rome in A.D.
164 he found the followers of Erasistratus opposing venesection. Galen
opened up discussion with these physicians in two books, _Against
Erasistratus_ and _Against the Erasistrateans Dwelling in Rome_. These
argumentative dialectical treatises, together with his _Therapeutics of
Venesection_, in which he presented his theory and practice of
venesection, established Galen's views on bloodletting, which were not
effectively challenged until the seventeenth century.[6]

The fundamental theory upon which explanations of health and disease were
based, which had its inception in ancient Greek thought and lasted up to
the eighteenth century, was the humoral theory. Based on the scientific
thought of the Pre-Socratics, the Pythagoreans, and the Sicilians, this
theory posited that when the humors, consistin