21 Grams: The Weight of The Soul

Jan 3, 2022 1 comments

What is a soul? Can it be touched? Does it have mass? These questions tormented Duncan MacDougall, a physician from Haverhill, Massachusetts, so much that he devised an experiment to determine whether souls have physical weight. 

“The soul leaving the body” by Luigi Schiavonetti, circa 1810.

MacDougall postulated that the soul was material and therefore, there should be a measurable drop in the weight of a person when the soul departed the body. In 1901, MacDougall selected six terminally ill patients from a nursing home, four suffering from tuberculosis, one from diabetes, and one from unspecified causes. MacDougall specifically chose people who were suffering from conditions that caused physical exhaustion, as he needed the patients to remain still when they died to measure them accurately. MacDougall then rigged a special bed in his office that sat upon an industrial sized platform beam scale sensitive to two-tenths of an ounce, or about 5.6 grams. Upon this bed he placed, in succession, the six patients, and observed them before, during, and after their death, measuring any corresponding changes in weight. MacDougall meticulously recorded his observations:

The patient’s comfort was looked after in every way, although he was practically moribund when placed upon the bed. He lost weight slowly at the rate of one ounce per hour due to evaporation of moisture in respiration and evaporation of sweat.

During all three hours and forty minutes I kept the beam end slightly above balance near the upper limiting bar in order to make the test more decisive if it should come.

At the end of three hours and forty minutes he expired and suddenly coincident with death the beam end dropped with an audible stroke hitting against the lower limiting bar and remaining there with no rebound. The loss was ascertained to be three-fourths of an ounce.

This loss of weight could not be due to evaporation of respiratory moisture and sweat, because that had already been determined to go on, in his case, at the rate of one sixtieth of an ounce per minute, whereas this loss was sudden and large, three-fourths of an ounce in a few seconds. The bowels did not move; if they had moved the weight would still have remained upon the bed except for a slow loss by the evaporation of moisture depending, of course, upon the fluidity of the feces. The bladder evacuated one or two drams of urine. This remained upon the bed and could only have influenced the weight by slow gradual evaporation and therefore in no way could account for the sudden loss.

There remained but one more channel of loss to explore, the expiration of all but the residual air in the lungs. Getting upon the bed myself, my colleague put the beam at actual balance. Inspiration and expiration of air as forcibly as possible by me had no effect upon the beam. My colleague got upon the bed and I placed the beam at balance. Forcible inspiration and expiration of air on his part had no effect. In this case we certainly have an inexplicable loss of weight of three-fourths of an ounce. Is it the soul substance? How other shall we explain it?

MacDougall observed similar loss of weight in his other patients, but the results were not consistent. One of the patients lost weight but then put the weight back on, and two of the other patients registered a loss of weight at death which increased with the passage of time. Only one patient showed an immediate drop in weight amounting to three-fourths of an ounce, approximately 21.3 grams, coinciding with the time of death. MacDougall disregarded the results of the other two patients on the grounds the scales were “not finely adjusted”.

MacDougall then repeated his experiment with fifteen dogs. None of them registered a significant drop in weight, which Macdougall took as corroborating evidence, in keeping with his religious doctrine, that animals have no souls. While Macdougall's human subjects were all terminally ill patients, there is no explanation of how he came to be in the possession of fifteen dying dogs in so short a span of time, which can only be presumed that the good doctor had poisoned fifteen healthy dogs for his little experiment.

MacDougall did not publish his finding until six years later, citing that the experiment would have to be repeated many times before any conclusion could be obtained. It was published in 1907 in the Journal of the American Society for Psychical Research and the medical journal American Medicine. A story about the experiment also appeared in The New York Times.

Following the publication of the experiment in American Medicine, a debate ensued between physician Augustus P. Clarke and Duncan MacDougall, who exchanged letters back and forth with the former denouncing the validity of the experiment and the other defending his position. Clarke noted that at the time of death there is a sudden rise in body temperature as the blood stops circulating through the lungs where its air-cooled. This rise in body temperature would increase sweating and moisture evaporation which could easily account for MacDougall’s missing 21 grams. This would also explain why dogs didn’t lose weight after death as dogs do not have sweat gland and cool themselves not by sweating but by panting. Macdougall rebutted that circulation ceases at the moment of death and so the skin wouldn’t be heated by the rise in temperature.

Augustus P. Clarke wasn’t the only one to criticize MacDougall’s experiments. The doctor was roundly derided by the scientific community as being flawed and even falsified. His experiments have been stated as an example of selective reporting, as MacDougall ignored the majority of the results. Popular science author Karl Kruszelnicki criticized the small sample size, and questioned how MacDougall was able to determine the exact moment when a person had died considering the technology available at the time. Because his experiments were not replicable and his results unreliable, MacDougall’s 21 grams experiment was given little credence by scientists of the time.

Duncan MacDougall.

Undeterred by the skepticism, MacDougall moved on to the next phase of his experiments—photographing the soul at the moment it left the body. In 1911, the New York Times:

Dr. Duncan MacDougall of Haverhill, who has experimented much in the observation of death, in an interview published here to-day expressed doubt that the experiments with X rays about to be made at the University of Pennsylvania will be successful in picturing the human soul, because the X ray is in reality a shadow picture. He admits, however, that at the moment of death the soul substance might become so agitated as to reduce the obstruction that the bone of the skull offers ordinarily to the Roentgen ray and might therefore be shown on the plate as a lighter spot on the dark shadow of the bone.Dr. McDougall is convinced from a dozen experiments with dying people that the soul substance gives off a light resembling that of the interstellar ether. The weight of the soul he has determined to be from one-half ounce to nearly an ounce and a quarter.

MacDougall did not have any more breakthroughs regarding his experiments with the human soul. His soul itself passed away into the other world in 1920.

Despite its rejection as scientific fact, MacDougall's experiment popularized the idea that the soul weighs 21 grams, and this idea has appeared in novels, songs, and movies. The title of the 2003 movie 21 grams was taken from this belief.



  1. You failed to mention he repeatedly acknowledged his experiments were not proof.


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