On this date, the English physician and scientist William Harvey was born. He is credited with being the first in the Western world to describe correctly and in exact detail the systemic circulation and properties of blood being pumped around the body by the heart. Harvey published his discovery in a treatise entitled Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (On the Motion of the Heart and Blood in Animals) in 1628. Brief, well argued, and clearly written, De Motu Cordis is very probably the one and only great classic of Western science written before 1800 that is still widely read today. His discovery was dramatically confirmed later in the seventeenth century by microscopist Marcello Malpighi’s discovery of capillaries.
Functional knowledge of the heart and the circulation had remained almost at a standstill ever since the time of the Greco-Roman physician Galen – 1,400 years earlier. With Harvey, life began to receive mechanistic explanation. The essential idea of mechanistic explanation is that “natural” events have “natural” causes and can be explained by cause-and-effect relationships that do not involve special action of supernatural agency. This is fundamental to modern science.
Just as important was Harvey’s methodology. De Motu Cordis quickly became understood as a rejection of traditional methods. It was viewed as challenging the traditional system of deductive reasoning via syllogisms, instead advocating experimentation and sensory experience. The empirical methodology observable in Harvey’s work is now the acknowledged scientific method and has been universally adopted across all science and medicine.
Harvey clearly understood the implications of his work, for he wrote at the opening of Chapter VIII (“Of the abundance of blood passing through the heart out of the veins into the arteries, and of the circular motion of the blood”), in which he demolishes the core of the Galenic model:
Thus far I have spoken of the passage of the blood from the veins into the arteries….But what remains to be said upon the quantity and source of the blood which thus passes, is of a character so novel and unheard-of that I not only fear injury to myself from the envy of a few, but I tremble lest I have mankind at large for my enemies, so much has wont and custom become second nature. Doctrine once sown strikes deep its root, and respect for antiquity influences all men. Still, the die is cast, and my trust is in my love of truth and the candor of cultivated minds.
He also left a message in De Motu Cordis that is as true today as it was 500 years ago:
True philosophers, who are only eager for truth and knowledge, never regard themselves as already so thoroughly informed, [so that they do not] welcome information from whomsoever and from wheresoever it may come; nor are they so narrow-minded as to imagine any of the arts or sciences transmitted to us by the ancients, in such a state of forwardness or completeness that nothing is left for the ingenuity or industry of others. On the contrary, very many maintain that all we know is still infinitely less than all that remains unknown. [Nor] do philosophers pin their faith to others’ precepts in such [ways] as they lose their liberty, and cease to give credence to the conclusions of their proper senses. Neither do they swear such fealty to their mistress Antiquity, that they openly, and in sight of all, deny and desert their friend, Truth. [emphasis added]
In Exercitationes de Generatione Animalium (On the Generation of Animals) in 1651, Harvey was extremely skeptical of spontaneous generation and proposed that every living animal originally comes from an egg, introducing the oft-quoted phrase “ex ova omnia” (all [life] from eggs). [However, Harvey did not completely reject spontaneous generation.] His experiments with chick embryos supported the theory of epigenesis, which states that organisms develop from substances in the egg that differentiate during embryonic development. This was in conflict with the now-descredited preformationist view that perfect miniature versions of offspring exist in the gametes and grow during development. [Please note that the term 'epigenesis' carries different meanings. Here, it used used in the older sense, as a theory of animal and plant development. In more modern times, it refers to mechanisms by which gene regulation over generations is controlled by elements other than DNA.]
- Schultz, S.G., “William Harvey and the circulation of the blood: The birth of a scientific revolution and modern physiology,” News in Physiological Sciences 17: 175-180 (Oct 2002).