Basic anatomy is not obvious
Two anatomical facts that are common knowledge now but were not always so
A general belief I have is that almost everything is less obvious than people think, even things that we may think are blatantly obvious or common sense. That is why I chose the name It’s Not Obvious for the blog.
There are many ways one could illustrate this. Today I will provide historical accounts of how two basic facts about anatomy were discovered: that blood circulates in the body and that urine flows from the kidney to the bladder.
Blood circulates in the body
Here is an excerpt from the paper by William Harvey, On the motion of the heart and the circulation of the blood, in which they reveal their grand idea that blood circulates in the body.
(The grammar and sentence structure of the original paper is dense and hard to read, so I have modified it to make it easier, while maintaining the tone. However, it is still tricky to read so do not be surprised if you need to re-read any of it.)
But what remains to be said upon the quantity and source of the blood is of so novel and unheard-of character that I not only fear injury from the envy of a few, but I tremble lest I have mankind at large for my enemies, so much does custom, doctrine and respect for antiquity influence all men. Still the die is cast, and my trust is in my love of truth.
When I surveyed my mass of evidence, whether derived from:
vivisections and my reflections on them,
the ventricles of the heart and the vessels that enter into and out of the ventricles,
the arrangement and intimate structure of the valves and of the other parts of the heart in general,
or many things besides,
I frequently and seriously thought what might be the quantity of blood which was transmitted and in how short a time it was transmitted, and was not finding it possible this could be supplied by the liquids from consumed food and drink, unless the blood should somehow find its way from the arteries into the veins, and so return to the right side of the heart; I began to think whether there might be a motion, as it were, in a circle.
[Two pages of reasoning and estimates of volumes of blood pumped]
But indeed, supposing even the smallest quantity of blood to be passed through the heart with each pulsation, a vastly greater amount would still be thrown into the arteries and whole body than could by any possibility be supplied by the food consumed; in short it could be furnished in no other way than by making a circuit and returning.
When I first read this, I was utterly confused. Isn’t it obvious that blood flows around the body? What else could it be?! What surprises me in particular about this is how late this discovery was made: the paper is from 1628!
Urine flows from the kidney to the bladder
The next excerpt is from a review of the book On the Natural Faculties by the Ancient Greek physician Galen.
Asclepiades, one particularly hated adversary of Galen, is charged with “bidding us distrust our senses where obvious facts plainly overturn his hypotheses.” Asclepiades has rather unusual opinions about the urinary system.
[…]
The most extreme example comes from a debate with the disciples of Asclepiades about the function of the ureters, trying to convince this rival school that urine flows from the kidneys to the bladder through these channels. After exhausting his rhetorical options, Galen turns to empirical anatomy. First he shows them, in a dead animal, that the ureters connect the two structures. This isn’t enough. Next he shows them “in a still living animal, the urine plainly running out through the ureters into the bladder.” This doesn’t change their minds either.
Next he takes a live animal, ligates the ureters, bandages the animal up, and lets it go. When he opens it up again later, he finds the ureters “quite full and distended”, and when he removes the ligature, everyone can see the urine flow into the bladder.
You’d think the story would end there, but not so. Instead, says Galen, “tie a ligature round [the animal’s] penis and then … squeeze the bladder all over.” He points out that nothing goes back through the ureters to the kidneys, demonstrating that the conveyance is a special, one-way action. He goes on like this for a while. Let the animal urinate and tie a ligature around one ureter but not the other. Cut open both the ureters and see the urine “spurt out of it”. Bandage the animal up and open him up later to discover his insides full of urine and the bladder empty. “Now, if anyone will but test this for himself on an animal,” Galen concludes, “I think he will strongly condemn the rashness of Asclepiades.”
The tone of this excerpt is certainly different from the first, but it highlights again the idea that things which can appear obvious are not, and that to establish these basic facts requires some (gruesome) creativity.
Concluding Remarks
It is possible you do not find these examples as notable as I do, but I hope it does illustrate the idea that things which we think of as obvious are not obvious, and it required significant insight and iterations of thought to arrive at the obvious knowledge. I would be curious to know if you have examples of your known.
To end, here’s a quote from Roman philosopher Seneca who expresses this thought:
The time will come when diligent research over long periods will bring to light things which now lie hidden. A single lifetime, even though entirely devoted to the sky, would not be enough for the investigation of so vast a subject… And so this knowledge will be unfolded through long successive ages. There will come a time when our descendants will be amazed that we did not know things that are so plain to them.