The English physician William Harvey (1578-1657) presented in his treatise De motu cordis (1628) on the circulation of the blood not only a new model of the heart and blood, but also a clear, cogent argument built on observational and experimental evidences. It was a guide to proceeding experimentally in the study of the body’s systems, and a model for reasoning in the demonstration of a cause and an explanatory system. In later philosophical terms, we would say he demonstrated the existence of a new cause (heart-as-pump pushing the blood in a circuit), its competence to produce the effects to be explained (heart’s motion, structure of heart and vessels, blood flow, pulse, difference between vein and artery, difference between venous and arterial blood), and the responsibility of the cause in actual production of the effects (the only theory that can explain all the facts).

The presentation used traditional Aristotelian logic and meaning, although calling for a correction of the ancients and the exploration of new ideas. Harvey presented quite radical observational and experimental techniques on both dead (dissection) and living (vivisection) animals. Combining observation, measurement, logic, and new mechanistic imagery for the operation of the parts, he made it all seem quite common-sensical. He defended the new view as the only one consistent with new and old observations or facts. It also was the best possible account to tie all the facts together; no other theory could explain or connect so much. That claim included his deductions about medical problems, even if not much was suggested for new therapeutics. The power of Harvey’s presentation an-d argument lay in its use of individual, repeatable observations that all come together to support the logical conclusion.

He presented his evidence and argument in a treatise that was not illustrated with the anatomical investigations. He relied upon detailed description, always tied to the logic of how the parts worked.

Go to some selections from the text, which illustrate his style of persuasion, his experiments and types of evidence, and the logic of his argument.

As a guide to the structure, here are his chapter headings, with my description of how he argues in each section:

Introduction: In which is shown the relative weakness of previous accounts of the movement and function of the heart and arteries

[He confronts the previous explanations with empirical observations and logical contradictions. He draws on the principle of connecting structure to function or action. His standard style is that of Scholastic disputation: cite authority, use an observation, find logical consistency — but he does to raise a series of questions that challenge earlier authorities on the heart and blood systems.]

1: The Author’s Motives for Writing

[He expects resistance to overturning ancient authority with new ideas, and justifies his work, while acknowledging the difficulty of the observations.]

2: On the Motions of the Heart, as Seen in the Dissection of Living Animal

[His new technique of doing the dissection of living animals, to observe the actions inside the body, lets him see new details that demand new explanations of the contents of the blood vessels, the cause of the pulse, and the action of the heart to propel the blood.]

3: Of the Motions of the Arteries, as seen in the Dissection of Living Animals

[The contraction of the heart is shown to cause the arterial pulse, both by observation and by simple experiments on the parts.]

4: Of the Motion of the Heart and Its Auricles, as Seen in the Bodies of Living Animals

[He demonstrates the sequence of the movements of the chambers of the heart, by observation of failing hearts. He continues to confront older theory with these new observations and the logical impossibility of the older theory, now replaced with new functional description that accounts for all the facts.]

5: Of the Motion, Action and Office of the Heart

[Summing up chapters 2 to 4, he provides a complete description of the heart’s motion as the pump that in sequence propels the blood through the body. He acknowledges it looks like one motion, but is simply like a machine so fast its sequential actions appear simultaneous. The description makes a harmonious connection of all the parts and motions to the new function of driving the blood.]

6: Of the Course by Which the Blood Is Carried from the Vena Cava into the Arteries, or from the Right into the Left Ventricle of the Heart

[The argument is that a single case is not sufficient to see the way it works, so he adds comparisons with simpler systems in animals with fewer parts. They are most helpful when they lack the parts that confuse us, such as the heart-lung circuit. And the observation of dead bodies is not sufficient; one needs to observe and manipulate living systems.]

7: The Blood Passes Through the Substance of the Lungs from the Right Ventricle of the Heart into the Pulmonary Veins and Left Ventricle

[Here’s a case where Galen’s ideas help him, as he can appeal to theories of blood passing through the lungs and use Authority to confirm those ideas. This is mostly an argument by disputation, emphasizing text and principles.]

8: Of the Quantity of Blood Passing Through the Heart from the Veins to the Arteries; And of the Circular Motion of the Blood

[He starts by once again rhetorically justifying the presentation of radical new ideas — because he’s proposing the most radical thing in the treatise with the idea of the circulation of the same blood through the body. This requires blood to move in new ways from veins to arteries, and it overturns the Galenic idea of constant production of new blood used up by the body. He starts with an analogy, to the sun as the center of cosmic “circulation.”]

9: That There Is a Circulation of the Blood Is Confirmed from the First Proposition

[These next three chapters are different proofs for the new circulation theory. First, blood pushed out of the heart with each beat leads to far more blood than could possibly be created each day from the food one eats. He does a very new thing: measures the volume of each heartbeat, and extrapolates the volume of blood that moves. It’s an argument of logical consistency. He then connects the idea of a constant volume moved through the body to explain other observations.]

10: The First Position: Of the Quantity of Blood Passing from the Veins to the Arteries. And That There Is a Circuit of the Blood, Freed from Objections, and Farther Confirmed by Experiment

[These experiments are on a simpler system, a snake with fewer parts.]

11: The Second Position Is Demonstrated

[This experiment is on the pulse, as the outcome of blood being driven to all parts of the body. He ties off vessels to show flow disrupted. It’s a logical argument of what happens, given the idea of directional flow that he got from experiments. He does correlate some medical conditions to his circulation theory here.]

12: That There Is a Circulation of the Blood Is Shown from the Second Position Demonstrated

[More argument based on the volume of blood, and the need to flow back to the heart.]

13: The Third Position Is Confirmed: And the Circulation of the Blood is Demonstrated from It

[The observation of dissected veins, showing flaps that are deduced to function as one-way valves, shows how the circuit works. This function of a part was not understood earlier, and how he can make sense of it. It is demonstrated with a simple experiment one can do on oneself — without cutting or blood. The technique is provided in the one illustration in the text – -see below]

14: Conclusion of the Demonstration of the Circulation

[A summation.]

15: The Circulation of the Blood Is Further Confirmed by Probable Reasons

[A return to disputation against the earlier authorities, but also providing new ideas about a theory of heart’s role as a primary seat of life.]

16: The Circulation of the Blood Is Further Proved from Certain Consequences

[Making a logically compelling case by drawing out deductions of what we ought to observe if he’s right.]

17: The Motion and Circulation of the Blood Are Confirmed from the Particulars Apparent in the Structure of the Heart, and from Those Things Which Dissection Unfolds

[Another summation, now with the demand for any critic to produce a theory that explains as much as Harvey’s does.]

Imagery

Harvey appealed throughout his text to dissections and difficult vivisections, including on small animals. This is not something many of his readers were likely to perform themselves. But in Chapter 13, wrapping up his last argument in his proof of the circulation, he must show that veins carry blood back to the heart. This can be known by dissection of the valves in the veins — now deducing their function and explaining what his teacher Fabricius could not . Far more impressive, because it was so obviously performable by any reader, was his demonstration from the living arm, without any cutting or bleeding. Perhaps it is little wonder then that this was the one illustration: how anyone could do a simple experiment and prove a fundamental new insight.

In addition to the physical experiments, Harvey made a rhetorical connection with the body/cosmos as microcosm/macrocosm, albeit with a new emphasis on circular motion:

“We have as much right to call this movement of the blood circular as Aristotle had to say that the air and rain emulate the circular movement of the heavenly bodies. The moist earth, he wrote, is warmed by the sun and gives off vapours which condense as they are carried up aloft and in their condensed form fall again as rain and re-moisten the earth, so producing successions of fresh life from it. In similar fashion the circular movements of the sun, that is to say, its approach and recession, give rise to storms and atmospheric phenomena.

It may very well happen thus in the body with the movement of the blood. All parts may be nourished, warmed, and activated by the hotter, perfect, vaporous, spirituous and, so to speak, nutritious blood. On the other hand, in parts the blood may cooled, coagulated, and be figuratively worn out. From such parts it returns to its starting-point, namely, the heart, as if to its source or to the centre of the body’s economy, to be restored to its erswhile state of perfection.

This organ deserves to be styled the starting point of life and the sun of our microcosm just as much as the sun deserves to be styled the heart of the world. For it is by the heart’s vigorous beat that the blood is moved, perfected, activated, and protected from injury and coagulation. The heart is the tutelary deity of the body, the basis of life, the source of all things, carrying out its function of nourishing, warming, and activating the body as a whole.”

And finally, to be truly in line with current fashion, he also alluded to mechanical wonders:

“These two movements, one of the auricles and the other of the ventricles, occur successively but so harmoniously and rhythmically that both appear to happen together and only one movement can be seen, especially in warmer animals in rapid movement. This is comparable with what happens in machines in which, with one wheel moving another, all seem to be moving at once. It also recalls that mechanical device fitted to firearms in which, on pressure to a trigger, a flint falls and strikes and advances the steel, a spark is evoked and falls upon the powder, the powder is fired and the flame leaps inside and spreads, and the ball flies out and enters the target; all these movements, because of their rapidity, seeming to happen at once as in the wink of an eye.”