William Harvey (1578-1657) was an English scientist, educated at Cambridge, who went to study in 1597 in Italy at the University of Padua, where the most advanced medical education was then available. He returned to England in 1602, and in 1618 he was appointed physician to the Kind, James I. He lectured at the Royal College of Physicians, and in 1628 published, in Frankfort, a work in Latin whose English translation is Anatomical Dissertation concerning the Motion of the Heart and Blood. In it, Harvey presented his evidence and argument for the following startling conclusion: the blood circulated in a system, leaving the heart through arteries, and returning via veings, in a cycle.
This contradicted the reigning system of physiology of the blood, that of Galen, the Roman physician of the second century AD, whose writings (originally in Greek) were taken as canonical both in anatomy and physiology. (Click here for a description of Galen's system). Just as Vesalius set a new standard for anatomy, displacing Galen's anatomy, so did Harvey set a new standard for physiology, yet again replacing Galen's physiology.
Galen had argued that the blood was produced in the liver, whence it was sent to the heart and then the brain, each time imbued with a new "spirit" which served an essential bodily function. (The "spirit" was not a ghostly entity, but the finest part of the blood produced by each organ system). (Click A Href="GalenPhysio.html>here for a more detailed presentation of Galen's system). The blood and its "spirited" component was consumed in this process, which had to be continually and constantly renewed. This was to be the weak point of the theory upon which Harvey would focus his criticism.
Harvey used experimental technique to make a number of key observations:
Let's see how he disproved Galen's claim on this point: The following diagram illustrates one of the major experimental techniques that Harvey used:
Illlustration of Harvey's experimental technique
|Essentially, what Harvey did was to "take the pulse" and calculate the amount of blood that would have to be produced, on Galen's system, each hour. The experimenter can be seen taking this pulse in the above drawing. Supposing an average of 72 pulses per minute, and two ounces of blood per pulse, that would make 72 x 60 x 2 ounces, or 540 pounds of blood per hour that would have to be produced. As the Galenic system had the blood derived from food, each individual would have to eat at least that much per hour just to stay alive! Obviously, this was contradicted by fact.|
Here are two selections from Harvey's work of 1628. The first is his preface, including a "Dedication" to the King and his "Greetings" to his colleagues of the Royal Society. You will notice a number of interesting rhetorical and theoretical points which Harvey makes:
You can also read a chapter and the conclusion of Harvey's work to see how he explained the experiment of taking the pulse to disprove Galen's theory.
Just as Vesalius had replaced Galen's anatomy, so too did Harvey replace Galen's physiology. These were two key elements of the scientific revolution in biology, to be continued (though not completed) by Linnaeus' system of species classification.