Sometimes Wrong, Never Unsure

Half of what we teach you is wrong. We just don't know which half.

In my first week of medical school, I sat with 300 classmates in an echoing auditorium heavy with history and anticipation. I felt like Hippocrates was looking down at me, maybe holding out a phantom hand, whispering to me: all of this is yours, now. I’m not one to overlook an opportunity for wonder, and I felt it in spades. The oil paintings on the walls, the polished wood podium, it was all just the way it was supposed to be. Up to and including the white-bearded, white-coated lecturer who stood at the front and told us the same joke he had clearly told every new class for the past two decades:

Welcome to medical school! In the next four years, half of what we’ll teach you here is going to be false. We just don’t know which half yet!

He winked, offering a touch of showmanship up the rows of seats, and 300 nervous first years erupted into laughter.

I didn’t laugh.

I was 22, and very naïve, and very over-awed. And I believed that I was stepping into a field that had things figured out. Not cured, you understand. I knew, of course, that there were lots of things we couldn’t fix. But I hadn’t made the conceptual leap from “unable to fix” to “not understood.” Knowing that we can’t cure cancer is very different from realizing we don’t fully understand it. And recognizing that our understanding is incomplete is only the first ice floe in the ocean of epistemological realizations. The second jump is when you recognize that some of what we do know will be overturned with new knowledge. As that realization hit me, I felt like some part of the foundation of my world had cracked, just a little.

I didn’t yet appreciate that I was entering into a tradition built on incomplete understanding. If Hippocrates had any message to pass down to me, this was it. My professor may have overestimated the percentage, but he was sharing a fundamental truth about our new field. The world does not wait for human omniscience; patients present with diseases long before doctors know how to treat them. And what then? In our earliest histories, people used plant-based pharmacology to treat the symptoms with a heartfelt appeal to the unknowable divinities who were believed to cause the problem. The earliest healers relied on their senses for anatomy and pharmacology. For physiology, they looked to the gods.

It was in Ancient Greece that the search for reasons transitioned from the supernatural to the natural. While Hippocrates is remembered today largely for his eponymous (and mistranslated) oath, he earned the title “Father of Medicine” for bringing the field from the ordained to the observable. Unlike his contemporaries, he rejected divine punishment or demonic possession as an explanation for illness. He focused, instead, on what could be perceived with the senses, and he pushed his students to do likewise. Before radiology, before germ theory, before microscopes— Hippocrates did not yet understand the cause of any specific disease. But he put the nature of health and illness into the realm of the understandable, and medicine began. Aristotle, although speaking of himself, described the impact of Hippocrates as well when he said:

Mine is the first step and therefore a small one, though worked out with much thought and hard labor. You, my readers or hearers of my lectures, if you think I have done as much as can fairly be expected of an initial start... will acknowledge what I have achieved and will pardon what I have left for others to accomplish.

The early explanations of health and disease, physiology and pathophysiology, often sound absurd to our modern ears. Take, for example, the pneumatic theory of circulation, first proposed about 150 years after Hippocrates by the Greek anatomist Erasistratus. This theory prevailed for more than 1500 years- until William Harvey famously cut open a pig on a lecture hall stage to disprove it. Among other things, the pneumatic theory argues that there is a ‘pneuma,’ or vital spirit that is essential to health, that travels in the arteries. In this theory of circulation, blood enters the lungs through the pulmonary artery and, by the time it leaves the lungs again, transforms into the invisible pneuma. That pneuma travels throughout the bloodless arterial system, where it enables thought, feeling, and function.

How did the greatest minds of Ancient Greece reach a conclusion so misguided? Especially since they were proponents of a natural, observable theory of disease, and “the gods did it” was no longer an accepted answer. They drew conclusions based on what they knew. The first thing they knew was that the arteries were empty of contents. Unlike veins, which carried blood, the arteries must have some unseen purpose. Hence the concept of the unseeable pneuma. So how could Hippocrates, Aristotle, and Erasistratus know that arteries are empty, when every school child today knows they are full of blood? Their source of information was, primarily, the body after death. In a corpse, the thick-walled arteries drain quickly of blood, which pools and collects in the thin-walled and expandable veins. The result is that when our early anatomists conducted an autopsy, they found a system of empty tubes.

These empty tubes- the arteries- connected to the lungs. The lungs connected to the outside world via the trachea, or windpipe. Open your mouth and take a deep breath. It’s obvious that you take in air through the windpipe. As anatomists dissected the heart, they found a similar contradiction: the thick-walled left side of the heart is empty of blood in a corpse more than a few hours old, as it quickly pools in the lower pressure right side. The observers saw a system of veins full of blood, and a system of empty arteries. They concluded- reasonably!- that the visible blood, once it entered the lungs, must transform into the invisible substance that filled the arteries. Pneuma.

You might be thinking: “That’s all well and good, ancient anatomists, but surely one of you must at some point witness a living person who receives an arterial injury? Or even butcher an animal? You must see the blood spurt forth and realize that arteries are not full of air?” They noticed that, too, and had an explanation for it. Nature, Aristotle himself explained, abhors a vacuum. When an artery in a living being is opened, the negative pressure pulls blood from nearby veins to draw it into the damaged space. This explains why the empty arteries can bleed, and why the pressure of that bleeding is so much higher than a cut vein.

I wonder if, when students sat at Hippocrates’s feet and began to study with him, he told them gently, “My students, half of what I will teach you may be false. I don’t know yet which half.” Perhaps they laughed. Perhaps one of them was shocked. The reality of medicine is a need to act in a world of incomplete knowledge. An absolute need in the absence of absolute truth. So all students of medicine learn that lesson eventually, and all of the great minds that have pushed medicine forward encounter it constantly. Surgeons, it is said, are “sometimes wrong, but never unsure.” They cannot afford to be unsure, when the disease is certain; they cannot afford doubt, when the choices are absolute. Cut, or don’t cut; the structure bleeds, or it doesn’t. Sometimes what we know is proven wrong. Sometimes what we don’t know is proven essential. Sometimes people die in that space of the unknown. And the surgeon’s task is to accept, and start again the next day. For the anatomists who move the world forward, it’s fuel: not for uncertainty, not for doubt, but for a better understanding of the world tomorrow than we have today.