On the Motion of the Heart and Blood in Animals (De Motu Cordis)

Summary

On the Motion of the Heart and Blood in Animals is the short Latin treatise, printed at Frankfurt in 1628, in which William Harvey argued that the blood moves continuously in a circuit, driven out by the heart through the arteries and returned to it by the veins. The library text is Robert Willis's English translation of 1847, as revised by Alexander Bowie and reprinted in 1910 in the Harvard Classics, with that series' introductory note on Harvey's life. The book opens with a dedication to Dr. Argent, President of the College of Physicians, reminding the Fellows that they had watched Harvey's demonstrations for more than nine years. He declares that he learns and teaches anatomy from dissections, not books, and that he means no disrespect to the ancients. A long Introduction then reviews the received teaching, largely Galen's: arteries draw in air and spirits, blood is made in the liver and seeps outward through the veins to nourish the body, and some passes from the right to the left ventricle through pores in the septum. Harvey raises objection after objection, asking why the arteries of fish, whales and the unborn child should draw in air at all. Chapters I to V record what he saw in living animals, chiefly cold-blooded ones whose hearts beat slowly: the heart contracts, hardens and grows pale as it expels blood, and the arteries swell because they are filled, not because they expand of themselves. Chapters VI and VII trace the passage of blood from the right ventricle through the lungs to the left, drawing on the fetal heart and on Realdus Columbus. Chapter VIII states the novelty Harvey fears to announce, and Chapter IX supplies the famous calculation: even if the heart expels only a drachm per beat, a thousand beats in half an hour move more blood than food could ever replace, so the same blood must return. Chapters X to XIII prove three propositions by experiment, including ligatures on the human arm and the valves in the veins first figured by his teacher Fabricius, which let blood flow only toward the heart. Chapter XIV states the conclusion in one sentence, and Chapters XV to XVII add supporting reasons from heat, from the spread of contagion and of externally applied medicines through the body, and from comparative anatomy. The argument persuaded slowly. Jean Riolan the Younger and others opposed it, Descartes accepted the circulation while disagreeing about the heartbeat, and the capillaries Harvey had to infer were seen by Marcello Malpighi in 1661.

Top Lessons

• Counting can overturn a theory

  Harvey's decisive argument in Chapter IX is arithmetic. By granting his opponents the smallest plausible output of the heart and multiplying by the number of beats, he shows that the liver could not possibly make so much new blood. The lesson is that a simple measurement, honestly carried through, can decide between explanations that observation alone leaves open.

• Respect for the ancients and the duty to correct them

  Harvey honors Galen, borrows his experiments and calls Fabricius a venerable teacher, yet he concludes that the inherited account of the blood is wrong. He shows that one can correct a master in the master's own manner, by observation and argument, without contempt.

• Seeing and inferring

  Harvey could not see the tiny vessels that join arteries to veins; he inferred that blood passes through the 'porosities of the flesh' because the quantities and the valves required it. Good science often affirms what reasoning demands before instruments can show it, while remaining open to confirmation.

• Courage to publish

  In Chapter VIII Harvey admits that he trembles lest he make all mankind his enemies, because custom becomes a second nature. He publishes anyway, trusting in his love of truth. The book is a model of intellectual courage joined to careful preparation.

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Medical Lens

De Motu Cordis is a foundation text of physiology and of experimental medicine. Its method joins vivisection of many animals, ligature experiments on the living human arm, the anatomy of venous valves, and a quantitative estimate of cardiac output. Harvey's account displaced the Galenic model in which the liver continually makes blood and the arteries carry spirit, though he kept much traditional vocabulary: native heat, spirits, concoction and the heart as the seat of life. The clinical observations are drawn from the phlebotomy of his day: the fillet tied above the elbow, the fainting patient whose blood only drips. Chapter XVI uses the circulation to explain why a bite or venereal infection in one place can affect the whole body and why medicines applied to the skin act internally, an early physiological account of how disease and drugs spread through the whole body. Harvey also notes that the speed of the circulation varies with sleep, food, exercise and the affections of the mind, and that fear and faintness weaken the heart's action. Later physiology, including Malpighi's capillaries and Lower's work on the colour of blood, completed what Harvey left unexplained.

• Introduction

  Harvey sets out and examines the Galenic teaching on arteries, spirits, pores in the septum and the uses of the pulse.

• Chs. II–V

  Observations from vivisection of cold-blooded and warm-blooded animals establish that the heart's active phase is contraction.

• Ch. IX

  The calculation of blood expelled per beat and per half hour, which makes a circulation necessary.

• Chs. XI–XII

  Tight and medium ligatures on the arm, as used in bloodletting, show arterial inflow and venous return; the fainting patient whose blood only drips is explained.

• Ch. XIII

  The valves of the veins, figured by Fabricius, are shown to permit flow only toward the heart.

• Ch. XVI

  Contagion, poisoned wounds, rabies, the lues venerea, tertian fever and externally applied medicines are explained by the returning current of blood.