The Circulation of the Blood
Three theories of circulation competed in France after 1628: the hypotheses of William Harvey, Jean Riolan, and René Descartes. Harvey claimed that blood made a complete circuit of the body, that the heart pumped it into the arteries, that blood then passed to the veins and returned to the heart, and that blood nourished and heated the body. He believed that the heart, veins, and arteries were "constructed for that purpose with extreme foresight and wonderful skill," and thus that their structures revealed their functions. Descartes and Riolan accepted the idea of circulation. But they disagreed with Harvey about important details, challenging, for example, his estimate of the speed with which blood circulated. As a result, they proposed alternative explanations of the motions of the heart, and they retained certain elements from ancient theories about the motion of the blood. French botanists who wished to formulate an analogical theory of the circulation of sap had, therefore, three models from which to choose. None, however, was perfectly compatible with vegetable anatomy and physiology. These models must be clear if the theories of the circulation of the sap are to be understood.
Harvey's theory was the most important and was widely accepted in scholarly circles by the late 1660s. It was novel in several respects: it unified the venous and arterial systems, described the pulse as a mechanical effect of the heartbeat, calculated the quantity of the blood, and characterized the circulation as a closed system in which all blood returned to the heart without being consumed. Harvey challenged standard notions about the hierarchy of bodily organs. He maintained that the blood was more important than the heart because it preceded the heart in the development of a fetus. He also claimed that the heart was formed prior to the brain and liver and was thus more important to life than either of those organs.
Harvey also retained certain traditional views. He believed, for example, that the purpose of circulation was to nourish and warm the body by generating heat and spirits necessary for life. This made a circulatory motion necessary, in his view, not only so that all the parts of the body "may be nourished, warmed, and activated by the hotter, perfect, vaporous, spirituous and, so to speak, nutritious blood," but also in order to repair the blood which "may be cooled, coagulated, and be figuratively worn out" in its travels. The heart held a special, beneficial position in the body, for it was the "source or the centre of the body's economy" and could restore blood "to its erstwhile state of perfection. Therein, by the natural, powerful, fiery heat, a sort of store of life, it is re-liquefied and becomes impregnated
To prove his theory, Harvey tested and confirmed three assumptions. First, "the blood is continuously and uninterruptedly transmitted by the beat of the heart … into the arteries" in large quantities that cannot be made up by intake of food. Second, the pulse of the arteries drives the blood into every part of the body, in greater quantities than necessary for nutrition, and in such amounts that a rapid circular motion must be assumed. Finally, "the veins themselves are constantly returning this blood from each and every member to the region of the heart." As proof, Harvey cited his measurement of the amount of blood passing through the body in a half-hour; his experiments with ligatures of blood vessels; and his description of the structure and function of valves in the veins. Once the three suppositions were confirmed, Harvey could state "that the blood goes round and is returned, is driven forward and flows back, from the heart to the extremities, and thence back again to the heart, and so executes a sort of circular movement."
Although Peiresc and others in France defended Harvey's theory from the beginning, Riolan and Descartes both proposed alternative theories of the circulation of the blood. Riolan, a respected anatomist and member of the medical faculty of Paris, did not object to the idea of circulation in itself. But he found Harvey's formulation distasteful because it challenged Galen and undermined some of the theoretical bases of traditional medical practice. Riolan also mistrusted Harvey's assumption that the anatomy of animals may resemble that of humans.
Riolan argued that the blood traveled through the arteries and veins to the extremities of the body and returned to the heart two or three times a day. Not all blood returned to the heart, however, because some of it was assimilated into the body. Although the normal route of the blood was away from the heart in the arteries and to the heart in the veins, when the veins of the arms and legs threatened to become empty the blood in the veins of the trunk could flow backwards to prevent a void. Thus Riolan maintained conventionally that blood ebbed and flowed in the veins and that it was consumed as nutriment by the parts of the body.
Riolan also calculated the amount of blood in the heart and the entire body and the quantity of blood that passed through the body in one hour. But he disagreed with Harvey. Riolan did not believe that the heart propelled the blood, as Harvey had shown. Instead he claimed that the blood kept the heart in motion, as a stream moves the wheel of a water mill. In
Riolan's view, blood prevented the heart from drying out, while the heart reheated the blood and replenished it with spirits. Although Riolan agreed with Harvey about that function of the heart, he contradicted him in insisting on the primacy of the liver.
Descartes's theory was closer than Riolan's to Harvey's. Thus Descartes accepted the full circulation of the blood through the body, but he rejected Harvey's theory of the motion of the heart. Arguing that physiological phenomena resulted from chemical processes, Descartes claimed that when the wet blood reached the hot heart it vaporized and expanded. This stretched the heart. As the blood cooled, it condensed, and the heart contracted. This alternate vaporizing and condensation accounted, in Descartes's system, for the heartbeat and pulse.
Both Descartes and Riolan agreed with Harvey that there were anastomoses connecting the arteries to the veins. Descartes incorrectly gave Harvey credit for discovering them, although Harvey had simply assumed they existed. Descartes accurately summarized three of Harvey's proofs for the circulation, namely the argument from ligation, the argument from the function of valves in the veins, and the fact that all blood in the body can exit from one cut artery. But he did not stress Harvey's estimate of the amount of blood that passes through the heart in an hour. Like Harvey and Riolan, Descartes believed that circulating blood carried heat and nutrition to the body. Like Harvey, he argued that blood was not itself a nutriment but carried food. In order to explain how the body obtained this food, Descartes drew on an analogy with sieves, which permit small particles to pass but retain larger ones. Descartes believed the heart repaired and renewed the blood. To explain the motion of the heart, Harvey and Riolan cited mechanical models — a pump and a mill — while Descartes, the mechanist, derived his explanation from chemical processes.
Harvey first published his theory in De motu cordis in 1628. It quickly found defenders and detractors in France. Although it was banned from the Parisian medical school, lecturers at the Jardin royal disseminated the theory, and by the 1660s a Harveian school had established itself in France, counting among its members Claude Tardy, Jean Pecquet, Jacques Mentel, Pierre Guiffart, Jean Martet, Jacques Chaillou, and Pierre Betbeder. Several defended the Harveian theory of circulation in vernacular treatises about such topics as the lacteal veins, the lymphatic vessels, chyle, and the preparation of blood. Their affiliations reveal that medical faculties had become receptive to the theory of circulation and that even physicians educated by faculties hostile to the theory might adopt it. Tardy was physician to the duke of Orléans and doctor regent at the Parisian medical
faculty. Chaillou practiced medicine at Angers. Martet was a master surgeon and royal anatomist in the faculty of medicine at Montpellier. Mentel had been educated in medicine at Paris in the late 1620s and early 1630s. Pecquet corresponded with Harvey and became one of the original members of the Academy. Most of Harvey's defenders published in the vernacular, perhaps hoping, as Guiffart put it, to reach a less dogmatic audience. Harvey's French proponents stressed his quantitative findings (although they gave different figures) and his experiments with ligatures, but they relied far less on analogies to explain the theory than had Harvey.