Who would have thought it? At the exact moment of death, you, me, and everyone else, will lose precisely 21g in weight. Just like that. Gone. I know because it says so on the poster for Alejandro González Iñárritu's new movie called, as it happens, 21 Grams and starring Benicio del Torro, Sean Penn and Naomi Watts.
The movie's promotional blurb moves quickly to quash those tempted to guestimate how much body fluid and gas one might expel in a parting gesture to cause a 21g drop in weight by inquiring: "Is it a person's soul that constitutes those twenty one grams?" (Quick answer: no.)
"I've been dealing with death for 45 years and I can say with some confidence there's nothing in it," says Robert Stern, a pathologist at the University of California, San Francisco.
So where does the 21g assertion come from? Who are the "they" who say we lose this amount as soon as our hearts squeeze their final beats and the electrical storms in our brains flicker and fade?
The origin of the 21g figure can be traced to Duncan MacDougall, a doctor working in Haverhill, Massachusetts in the early 1900s. MacDougall had a keen fascination with death and spent part of his career on an almost obsessive hunt for evidence of the soul. He thought that if humans had a soul, it must exist in the body as some kind of material. And that material must weigh something.
MacDougall set out to test his theory with what was an excruciatingly bad experiment. In 1907, the year Einstein applied the laws of gravity to his special theory of relativity, MacDougall published his findings in American Medicine.
MacDougall's paper reveals as much about the author as it does about the quality of work that could get into medical journals at the time. MacDougall describes how he set about converting a hospital bed into a rudimentary balance so he could measure a patient's weight change as they died. The bed balance was sensitive, so to prevent his soon-to-be-dead patients from messing up his data, MacDougall hunted around for people who were dying of tuberculosis. As he noted: "It seemed to me best to select a patient dying with a disease that produces great exhaustion, the death occurring with little or no muscular movement, because in such a case, the beam could be kept more perfectly at balance and any loss occurring readily noted." In other words, there was to be no flailing around that could upset the scales.
In all, MacDougall managed to recruit a mere six dying people for his study, four of whom had tuberculosis. In turn, each was tucked up in his modified bed and their weight monitored until some minutes after their death. Any bowel movements or urination at death were fine, at least so far as the experiment was concerned, as it all stayed on the bed.
With a nod to best scientific practice, MacDougall then repeated the study with 15 dogs, which according to his religious beliefs, were not blessed with souls. It's not clear how MacDougall managed to get his dogs to die without rocking the bed, but some scientists suspect a nasty cocktail of drugs was used.
At the end of his foray into science, MacDougall declared that humans lost up to three-fourths of an ounce upon death, a figure that doesn't have quite the same ring as 21g, the metric equivalent. The dogs, he said, lost nothing. What else might it be if not the weight of the soul departing, he asked.
Before going public with his findings, MacDougall wanted to make sure that his patients' last breaths were not skewing his data, so he clambered on to the bed, (presumably once the last patient was removed and the sheets had been changed) and spent a few minutes exhaling. He then got a colleague to do the same thing. Neither managed to shift the balance enough to account for the weight loss MacDougall reported.
Despite the poor accuracy of his scales, the huge variability in his data, and the all-too-few people studied, MacDougall's experiment was also frustrated by the tricky skill of pinpointing the exact time of death. He was repeatedly challenged as to why the weight change on death appeared to take longer in some patients than others. To rebut the doubters, MacDougall wrote: "The soul's weight is removed from the body virtually at the instant of the last breath, though in persons of sluggish temperament, it may remain in the body for a full minute." He declared later in the paper: "Here we have experimental demonstration that a substance capable of being weighed does leave the body at death."
MacDougall's work was written up in the New York Times, which also covered his hope, some years later, to take a photo of the soul using x-rays. Despite being recorded in the paper that gives us all the news that's fit to print, his work is viewed with palpable embarrassment now. "It's simply not taken seriously," says Stern.
Gruesomely, Stern points out that dead bodies lose a lot of weight over time. Minute, intercellular structures called lysosomes release enzymes that break the body down into gases and liquid. "That's why, when you have mass graves, you can get explosions because of all the gas build-up," he says. "Just think if our bodies didn't break down. Everyone who had ever lived on the face on the Earth would still be here." Now, that would make a good movie.