Two hundred years ago, a Scottish medical student named Robert Christison watched a human vivisection.
It was inadvertent; the subject was meant to be dead. But in the days before people willingly left their bodies to science, surgeons stole them. The aftermath of judicial hangings was a competition between “the relatives and the [surgical] students—the former to carry off the body intact, the latter to dissect it,” Christison wrote in his autobiography. “Thus dissection was apt to be performed with indecent, sometimes with dangerous haste. It was no uncommon occurrence that, when the operator proceeded with his work, the body was sensibly warm, the limbs not yet rigid.” Hangings were sometimes ineffective, and the condemned survived. No wonder then that occasionally, in their rush, surgeons got it wrong and opened up a body to demonstrate its anatomy only to discover it was not yet a corpse.
Even if you're in less of a rush, simple observation has always been worryingly fallible when it comes to distinguishing life from death. When I was a junior doctor, I recall the hairs on the back of my neck slowly rising as I walked toward a patient's room. His family had just stopped me at the end of their visit, saying “I think we'll come back tomorrow, we've been sitting with him for an hour and he's seemed awfully quiet.” He would forever remain that way. I found I often made the reverse mistake: Walking into the room of an elderly patient, it could take some time to recognize their stillness as that of sleep.
Preceding generations adopted technological aids to help them. Holding a mirror over a face to see if it misted up could be genuinely useful. The stethoscope—invented by a French doctor, Rene Laennec, who was embarrassed by putting his ear to his patient's bosom—meant that respiration and heart sounds could be listened for more accurately. All this helped, but it didn't fully solve the problem.
The precise division between life and death has always been unclear. In the 18th century, the chemistry of living (organic) and nonliving (inorganic) things was held to be fundamentally different. Into the former, God placed a spark of life—meaning that biochemical processes were absolutely different from the chemical reactions that could be created by mankind or the natural world. That belief was shown false in the 1820s, when a German chemist, Friedrich Wöhler, synthesized the first organic molecules. But even today it lingers on: The vague way in which organic is used as a euphemism for healthy and good is its relic. Throughout the 19th century, the exact spark of life remained an object of great interest, and also of great doubt.
Discussions of the soul tended to lead nowhere, since that word meant so many different things to different people. It was hard to prove when the soul left the body because it was something whose nature and identity no one could agree on. Hence a favorite distinction between the living and the dead rested directly on the word of God. Leviticus 17:11 and 17:14 were clear: Blood was the stuff of life. William Harvey, who discovered how blood circulated, wrote that it was “the first to live and the last to die.” Blood was life. So long as it was liquid, life remained.
Hence Christison's alarm as he watched the surgeon cut into the warm body. “Fluid blood gushed in abundance from the first incisions through the skin … Instantly I seized [the surgeon's] wrist in great alarm, and arrested his progress; nor was I easily persuaded to let him go on, when I saw the blood coagulate on the table exactly like living blood.” Peer pressure overcame his qualms, however, and he not only released the surgeon but remained part of the attentive audience. He was convinced that the man was alive, but he became willing to watch all the same.
John Hunter, the greatest surgeon of the 18th century, also believed that those whose blood was liquid were still alive, yet he had no problem slicing their hearts out—or even, in the interests of science, tasting them. (Wishing to explore human sexual function, he acquired the corpse of a man who died in the moment before ejaculation. When held in the mouth, Hunter reported, the dead man's semen had a slightly spicy taste.) An appetite for knowledge has never been a guarantee of compassion or of respect for the wishes of the dead.
In the years since Hunter, though, these concerns have genuinely advanced. We're better at saying where life ends and better at honoring the physical remains and the last wishes of our fellows—which is not to say there isn't still room for improvement. For many decades, we accepted that people died when their heart stopped beating, that is, when it stopped circulating blood. Why did we hold onto that notion, even long after we understood that electrical activity was the fundamental substrate for our lives? Once more, the limitation was partly technical—a heartbeat is relatively easy to detect—and partly not. The idea that blood was the stuff of life lingered on, aided by the dual meaning of “heart” it helped bequeath to our language and our thoughts. Did the body Christison saw being opened still have a beating heart? Was it, in any real way, alive? It certainly was in Cristison’s eyes, but whether it would have been in ours is harder to say.
Once we became confident about the primacy of electrical activity in the brain as the sign of life, we were able to be more positive. The need for donated organs pushed changes in our definition of death, especially because an organ-transplant recipient’s prospects for survival are much better when the organ is taken from a donor with a beating heart. In 1968, the wonderfully named Ad Hoc Committee of Harvard Medical School argued that death should no longer be regarded as occurring when the heart stopped, but when electrical activity ceased in the brain. Once that was gone, so was the person.