Views of the circulation of blood before Harvey
At the time of Harvey's publication, Galen had been an influential medical authority for several centuries. Galen believed that blood passed between the ventricles by means of invisible pores. According to Galen's views, the venous system was quite separate from the arterial system, except when they came in contact through the unseen pores. Arabic scholar Ibn al-Nafis had disputed aspects of Galen's views, providing a model that seems to imply a form of pulmonary circulation in his Commentary on Anatomy in Avicenna's Canon (1242). Al-Nafis stated that blood moved from the heart to the lungs, where it mixed with air, and then back to the heart, from which it spread to the rest of the body. Harvey's discoveries inevitably and historically came into conflict with Galen's teachings and the publication of his treatise De Motu Cordis incited considerable controversy within the medical community. Some doctors affirmed they would "rather err with Galen than proclaim the truth with Harvey."Galen incompletely perceived the function of the heart, believing it a "productor of heat", while the function of its affluents, the arteries, was that of cooling the blood as the lungs "...fanned and cooled the heart itself". Galen thought that during dilation the arteries sucked in air, while during their contraction they discharged vapours through pores in the flesh and skin.
Until the 17th century, two separate systems were thought to be involved in blood circulation: the natural system, containing venous blood which had its origin in the liver, and the vital system, containing arterial blood and the 'spirits' which flowed from the heart, distributing heat and life to all parts. Like bellows, the lungs fanned and cooled this vital blood.
Pulmonary circulation was described by Renaldus Columbus, Andrea Cesalpino and Vesalius, before Harvey would provide a refined and complete description of the circulatory system.
On Animal Generation
Harvey's other major work was Exercitationes de generatione animalium (On Animal Generation), published in 1651. He had been working on it for many years but might never have finished it without the encouragement of his friend George Ent.
The book starts with a description of development of the hen's egg. The major part is theoretical, dealing with Aristotle's theories and the work of the physicians following Galen and up to Fabricius. Finally he deals with embryogenesis in viviparous animals especially hinds and does. The treatment is generally Aristotelian and limited by use of a simple magnifying lens.
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Needham claims the following achievements for this work. His doctrine of omne vivum ex ovo (all life comes from the egg) was the first definite statement against the idea of spontaneous generation. He denied the possibility of generation from excrement and from mud, and pointed out that even worms have eggs. He identified the citricula as the point in the yolk from which the embryo develops and the blastoderm surrounding the embryo. He destroyed once and for all the Aristotelian (semen-blood) and Epicurean (semen-semen) theories of early embryogeny. He settled the long controversy about which parts of the egg were nutritive and which was formative, by demonstrating the unreality of the distinction of the circulatory system.
Works
Harvey, William (1889). On the Motion of the Heart and Blood in Animals. London: George Bell and Sons. william harvey.
Harvey, William; Franklin, Kenneth J. (translator); Wear, Andrew (introduction) (1993). The Circulation of the Blood and Other Writings. London: Everyman: Orion Publishing Group. ISBN 0-460-87362-8.
The Works of William Harvey. Robert Willis (translator). London: Sydenham Society. 1847. Includes:
An anatomical disquisition on the motion of the heart and blood in animals
2 disquisitions addressed to John Riolan, including refutations to objections to the circulation of the blood
Anatomical exercises on the generation of animals. To which are added:
1) On Parturition
2) On the uterine membranes and humours
3) On conception
4) Anatomical examination of the body of Thomas Parr
5) Letters
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