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Harvey, William (1578-1657)

         English physician who, by observing the action of the heart in
         small animals and fishes, proved that heart receives and expels
blood during each cycle. Experimentally, he also found valves in the veins,
and correctly identified them as restricting the flow of blood in one
direction. He developed the first complete theory of the circulation of
blood, believing that it was pushed throughout the body by the heart's
contractions. He published his observations and interpretations in
Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (1628),
often abbreviated De Motu Cordis.

Harvey also noted, as earlier anatomists, that fetal circulation short
circuits the lungs. He demonstrated that this is because the lungs were
collapsed and inactive. Harvey could not explain, however, how blood passed
from the arterial to the venous system. The discovery of the connective
capillaries would have to await the development of the microscope and the
work of Malpighi. He was heavily influenced by the mechanical philosophy in
his investigations of the flow of blood through the body. In fact, he used a
mechanical analogy with hydraulics. He could not, however, explain why the
heart beats. Furthermore, Harvey used quantitative methods to measure the
capacity of the ventricles.

Harvey was the first doctor to use quantitative and observation methods
simultaneously in his medical investigations. In Exercitationes de
Generatione Animalium (On the Generation of Animals, 1651), he was extremely
skeptical of spontaneous generation and proposed that all animals originally
came from an egg. His experiments with chick embryos were the first to
suggest the theory of epigenesis, which views organic development as the
production in a cumulative manner of increasingly complex structures from an
initially homogeneous material.

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Eric W. Weisstein
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