One exception was the work of Galen, an immensely productive, Greek-speaking physician who lived much of his life in Rome. By the of his death around A.D. 201, the indefatigable Galen had written some 350 treatises detailing his own experimental work in anatomy and physiology. Although he added much to medical knowledge, his studies were based largely on monkeys and farm animals and thus were frequently unreliable in their conclusions about human anatomy. But the sheer prodigiousness of Galen's output and the aura of infallibility that surrounded him served to perpetuate his errors and stifle further research. His work would remain unchallenged until the 16th century, as though the Hippocratic teaching of detailed, objective studies had been forgotten.

Like Hippocrates, Galen had become a medical icon, and it would take a bold idol smasher to undo him. History found the perfect candidate in Andreas Vesalius, a contentious young Flemish physician who, in his single-minded pursuit of the correct human anatomy, cared not a whit about Galen's untouchable authority. Gifted with intelligence, drive and the courage to stick with his convictions, he went his solitary way, dissecting cadaver after cadaver until he had made enough unbiased observations to write a book that would forever transform medicine's image of the human structure. Vesalius was 29 when it was published in 1543. The anger first directed against him for daring to defy Galen's teachings was matched by his own contempt for those who took so long to accept the validity of his work.

The feisty spirit of Vesalius has pervaded the history of medical discovery--not the contentiousness, perhaps, but certainly the refusal to accept what is not verifiable by one's own observations and the willingness to stand alone when principle is involved. And always the capacity for hard work has been the glue that holds everything else together, the underlying characteristic that enables all of the other qualities to produce a successful conclusion.