William Harvey’s On the Movement of the Heart and Blood in Animals

When I was a teenager, I belonged to the Classics Club. Each month I was sent a box containing a couple books, which I’ld either purchase or return. Most of these were classics of the Western canon. Some of my favorites were Homer’s Iliad, Plutarch’s Lives, Meditations by Marcus Aurelius, A Tale of Two Cities by Charles Dickens, The Autobiography of Benjamin Franklin, and Selected Tales and Poems by Edgar Allan Poe.

One of the books I bought was The Beginnings of Modern Science: Scientific Writings of the 16th, 17th and 18th Centuries, edited by Holmes Boynton. Does this collection contain any biological or medical physics? Yes! The best example is an excerpt from William Harvey’s book On the Movement of the Heart and Blood in Animals (1628). The book was originally written in Latin, and the Classics Club edition was translated into English by R. Willis.

But lest anyone should say that we give them words only, and make mere specious assertions without any foundation, and desire to innovate without sufficient cause, three points present themselves for confirmation, which being stated, I conceive that the truth I contend for will follow necessarily, and appear as a thing obvious to all.

First, the blood is incessantly transmitted by the action of the heart from the vena cava to the arteries in such quantity that it cannot be supplied from ingesta, and in such a manner that the whole must very quickly pass through the organ.

Second, the blood under the influence of the arterial pulse enters and is impelled in a continuous, equable, and incessant stream through every part and member of the body, in much larger quantity than were sufficient for nutrition, or than the whole mass of fluids could supply.

Third, the veins in like manner return this blood incessantly to the heart from parts and members of the body.

These points proved, I conceive it will be manifest that the blood circulates, revolves, propelled and then returning, from the heart to the extremities, from the extremities to the heart, and thus that it performs a kind of circular motion.

Next Harvey does a back-of-the-envelope calculation of how much blood circulates through the body. This estimate sounds as if it could have appeared in Intermediate Physics for Medicine and Biology.

Let us assume, either arbitrarily of from experiment, the quantity of blood which the left ventricle of the heart will contain, when distended, to be, say two ounces, three ounces, or one ounce and a half; in the dead body I have found it to hold upwards of two ounces. Let us assume, further, how much less the heart will hold in the contracted than in the dilated state; and how much blood will project into the aorta upon each contraction;—and all the world allows that with the systole something is always projected, a necessary consequence demonstrated in the third chapter, and obvious from the structure of the valves; and let us suppose, as approaching the truth, that the fourth, or fifth, or sixth, or even but the eighth part of its charge is thrown into the artery at each contraction; this would give either half an ounce, or three drachms, or one drachm of blood as propelled by the heart at each pulse into the aorta; which quantity, by reasons of the valves at the root of the vessel, can by no means return into the ventricle.

Now in the course of half an hour, the heart will have made more than one thousand beats, in some as many as two, three, and even four thousand. Multiplying the number of drachms propelled by the number of pulses, we shall have either one thousand half ounces, or one thousand times three drachms, or a like proportional quantity of blood, according to the amount which we assume as propelled with each stroke of the heart, sent from this organ into the artery; a larger quantity in every case than is contained in the whole body! In the same way, in the sheep or dog, say that but a single scruple of blood passes with each stroke of the heart, in one half hour we should have one thousand scruples, or about three pounds and a half of blood injected into the aorta; but the body of neither animal contains above four pounds of blood, a fact which I have myself ascertained in the case of the sheep.

Upon this supposition, therefore, assumed merely as a ground for reasoning, we see the whole mass of blood passing through the heart, from the veins to the arteries, and in like manner through the lungs.

More about Harvey’s work can be found in Asimov’s Biographical Encyclopedia of Science & Technology.

HARVEY, William

English physician

Born: Folkestone, Kent, April 1, 1578

Died: London, June 3, 1657

…[Harvey] was more interested in medical research than in routine practice. By 1616, he is supposed to have dissected eighty species of animals. In particular he studied the heart and blood vessels… He determined the heart was a muscle and that it acted by contracting, pushing blood out. Through actual dissection he noted that the valves separating the two upper chambers of the heart (auricles) from the two lower (ventricles) were one-way. Blood could go from auricle to ventricle but not vice versa. There were one-way values in the veins too, these having been discovered by Fabricius. For that reason, blood in the veins could travel only toward the heart and not away from it….

When Harvey tied off an artery it was the side toward the heart that bulged with blood. When he tied off a vein the side away from the heart bulged. Everything combined to indicate that blood did not oscillate back and forth in the vessels as Galen… had believe but traveled in one direction only.

Furthermore Harvey calculated that in one hour the heart pumped out a quantity of blood that was three times the weight of a man. It seemed inconceivable that blood could be formed and broken down again at such a rate. Therefore it had to be the same blood moving in circles, from the heart to the arteries, from these to the veins, from those back to the heart. The blood, in other words, moved in a closed curve. It circulated.