It’s possible that many readers have seen the movie 21 Grams (directed by Alejandro González Iñárritu), in which Sean Penn, Naomi Watts, and Benicio Del Toro, among others, portray a series of interconnected stories around a car accident. Guillermo Arriaga, the screenwriter, took the title from a historical episode that the French writer André Maurois had already recounted in 1931 in his novel Le peseur d’âmes (The Weigher of Souls): the experiment conducted in the early 20th century by Dr. Duncan MacDougall, aiming to prove his theory that the weight people lose upon death is due to the soul being released from the body.

Duncan MacDougall practiced medicine in Haverhill, Massachusetts. Born in 1886, his earlier career as a physician had no significant impact. It was from 1901 onwards that he entered history by proposing the hypothesis that the slight weight loss experienced by corpses shortly after death could be attributed to the departure of the soul. This would imply not only the existence of the soul but also that it has mass and can be measured.

This remarkable proposal would have gone unnoticed if MacDougall had not set out to prove it scientifically, following the trend of grotesque experiments of the time.

To do this, he selected six patients from nursing homes who were on the verge of death. They varied in age, background, and diseases, with four suffering from tuberculosis, one from advanced diabetes, and the remaining one from an unspecified condition. When a patient entered the agonizing phase, he was transferred to a special bed designed to calculate the patient’s weight, including everything from clothing to sheets and blankets. The precision was industrial, with a minimal margin of error of 0.28 grams.

The first subject to die lost weight at a rate of one ounce per hour (28.7 grams) until he stopped breathing, and the amount suddenly jumped to 0.75 ounces (21.2 grams). The second lost 0.50 ounces (14.17 grams), but after auscultation, he was weighed again, and the reading increased to one and a half ounces (43.5 grams). The third lost half an ounce, which later turned into a full ounce (28.7 grams).

The fourth was excluded from the study because the weighing bed was not properly adjusted at the fateful moment. At the time of death, the fifth dropped three eighths of an ounce, which he later recovered, only to lose it gradually minutes later. Finally, the sixth also had to be excluded from the investigation because he died before the bed could be adjusted.

Parallel to the research with the elderly, MacDougall conducted another experiment with fifteen dogs. It is assumed that animals do not have souls or, at least, not of the same category as humans, so it could be interesting to check the results. It is said that he did not find enough sick dogs, so he himself was forced to euthanize them with some medication. In any case, he reported that the bodies of the dogs did not experience a noticeable weight loss.

The study’s conclusions were not published until six years later, in April 1907, in the prestigious journals Journal of the American Society for Psychical Research and American Medicine, under the grand title The Soul: Hypothesis Concerning Soul Substance Together with Experimental Evidence of the Existence of Such Substance. However, the month before, The New York Times had already gained access to the text, publishing an article titled “Soul has weight, physician thinks”.

Immediately, the scientific community outright rejected MacDougall’s work, considering it flawed in both substance and form. They criticized his weighing system, which they deemed insufficiently accurate for an objective of that nature, as well as the small number of subjects used, which fell far short of the ideal minimum. Regarding the latter, MacDougall himself admitted that the research should be repeated with an appropriate number of patients. He was also reproached for selectively using data, such as choosing the 21 grams of the first patient as the effective result without considering the others.

Renowned physician Augustus P. Clarke warned that at the moment of death, there is a sudden increase in body temperature because the lungs stop taking in air, causing postmortem sweating; those missing 21 grams could be attributed to this lost water.

He also explained that dogs lack sweat glands, so they would not lose weight through sweating like humans. MacDougall countered that not only do the lungs stop, but so does the heart, and therefore, there would be no such heating as there is no blood circulation. Thus began an interesting debate between the two physicians in the pages of American Medicine that lasted for several months.

Today, of course, the hypothesis of the 21 grams of the soul is dismissed by the academic world. It is considered that in 1901, there was no technology to accurately declare the moment of death, that the conclusions were deduced from the analysis of a single patient while ignoring the others, that the number of subjects in the sample was too small to be considered significant, and that the method used to weigh the bodies lacked the necessary precision. In other words, the same objections that had already been raised in 1908.

As for MacDougall, he did not give up and insisted on quantifying the soul, but from a different perspective. Thus, in 1911, he came up with the idea of trying to capture photographs of souls at the moment of leaving the body and claimed to have captured “a light similar to that of interstellar ether”. It may sound somewhat eccentric, but in the second decade of the 20th century, when theosophy, parapsychology, occultism, spiritualism, and other pseudosciences were in vogue, it was believed that photography could capture what the human eye could not see.

In fact, a few years later, in 1918, the famous case of the Cottingley Fairies occurred, in which girls presented photos of themselves playing with those mythological beings. The renowned writer Sir Arthur Conan Doyle betrayed the spirit of his main character, Sherlock Holmes, by accepting that montage (in case there is any doubt, the girls, now elderly, confessed in 1981 that it was indeed a hoax), although in his defense, it can be said that he was somewhat unhinged with the possibility of contacting his son, who died prematurely.

Moreover, as if photography were not enough, MacDougall also tried with X-rays, which William Röntgen had recently discovered in 1895. Using X-ray equipment, the persistent physician meticulously examined the bodies of several people on the verge of death and told The New York Times that he had managed to see the soul in twelve cases. Otherwise, he did not repeat the weight experiment, and he could only discovered the truth on October 15, 1920; firsthand, as it was the date he passed away.

This article was first published on our Spanish Edition on December 14, 2018. Puedes leer la versión en español en El médico que dictaminó que el alma pesa 21 gramos


Duncan Macdougall, The Soul. Hypothesis Concerning Soul Substance Together with Experimental Evidence of The Existence of Such Substance | Len Fisher, Weighing the Soul: Scientific Discovery from the Brilliant to the Bizarre | Michael T. Santini, Venus: Don’T Go There: What Science and Religion Reveal About Life After Death | Ben Thomas, The Man Who Tried to Weigh the Soul | Wikipedia

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