____________________________I listened to Sherwin Nuland's book about Leonardo on my way home from visiting out east. I noticed that Chris Nickson had blogged about it by trying to find one of Da VInci's quotes I had heard:
“Anyone who in discussion relies upon authority uses not his understanding but his memory.”
“Those who study the ancients and not the works of Nature are stepsons and not sons of Nature, the mother of all good authors.”
“The grandest of all books, I mean the Universe, stands open before our eyes.”
It was interesting to hear about how extremely Da Vinci had observed and also how importantly he viewed sight in relation to other senses and ways of knowing. He was interested in energy, movement, and the "rhythmic harmonies of life".
He wanted to understand the muscles around the mouth because of their importance in facial expressions and because of his idea that the face was expression of the soul.
He was more of an anatomist than I realized - where he went beyond dissecting to understanding underlying structures and processes. I also thought it was interesting that he saw nature as the ultimate instead of relying on explanations from "God" as most still did then.
Notes from Nickson of Nuland:
He developed techniques to convey information through his drawings using cross-sections and multiple angles. Remarkably, centuries would pass before anatomical drawings became accepted as crucial for learning anatomy – indeed in his review of the 1858 first edition of ‘Gray’s Anatomy‘, Oliver Wendell Holmes actually criticized the book for including drawings.
Among Leonardo’s countless achievements in anatomy were:
• the deduction of the hierarchical structure of the nervous system, with the brain as a command center.
• the deduction that it was the retina of the eye that was sensitive to light, not the lens as previously believed. He learned to dissect the fragile structures of the eye by inventing new methods that involved sectioning the eye after it had been fixed by heating in egg whites.
• discovering the lesions of atherosclerosis and their possible role in obstruction of the coronary arteries. Even more remarkably, he presciently attributed these lesions to an “overabundance of nourishment” from the blood.
• the identification of the heart as muscle and speculations on the origin of body heat and the heart’s activity. He also discovered that the arterial pulse corresponds to ventricular contraction and that the ventricle shortens during contraction.
•the development of an understanding of mechanics by replacing muscles with wires. This allowed him to foreshadow Sherrington’s theory of reciprocal innervation of antagonistic muscles working across joints in complementary fashion. He was also able to work out specific actions such as that of biceps brachii, which he showed not only flexes the elbow but also supinates the hand through its twisting action on the ulna.
• working out that the tumescent penis becomes erect by filling with arterial blood, rather than air as previously supposed.
• the first to state that the mother’s contribution to the inherited characteristics of the fetus are equal to that of the father.
According to Nuland, one of Leonardo’s most impressive discoveries concerned the obscure topic of how aortic valves close. He determined that the aortic valves close while the ventricle is still contracted. This occurred because of the pressure created by eddy currents generated by the effect of the sinuses of Valsalva on blood flow through the proximal aorta. Leonardo elegantly demonstrated this using a model of the proximal aorta and ventricular outflow tract through which he allowed water containing millet to flow; the millet allowed visualization of the patterns of current and turbulence created in the flowing fluid. The rest of the world had to wait over 400 years, until 1969, for this ingeniously worked-out theory to be conclusively proven and (re)discovered using dye and cineradiography methods.
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