What is a soul? Does she have mass? These questions plagued Haverhill physician Duncan McDougall so much that he developed an experiment to determine whether the soul has physical weight.

how much does a soul weigh

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McDougal postulated that the soul is material and therefore there must be a noticeable drop in a person’s weight when the soul leaves the body. In 1901, MacDougall selected six terminally ill patients from a nursing home, four with tuberculosis, one with diabetes, and one with unexplained causes.

McDougal specifically chose people who were suffering from conditions that cause physical debilitation, as he needed patients to remain still as they died in order to accurately measure their weight. McDougall then built a special bed in his office that stood on an industrial-sized platform scale sensitive to two-tenths of an ounce, or about 5.6 grams. On this bed he placed six patients in succession and observed them before, during and after their death, measuring any relevant changes in weight. McDougall carefully wrote down his observations.

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The comfort of the patient was taken care of in every way, although he practically died when he was laid on the bed. He was slowly losing weight at the rate of one ounce per hour due to the evaporation of moisture from his breath and the evaporation of sweat.

Here is how McDougall described the process of observing one of the patients:

“After three hours and forty minutes, he died, and suddenly, coinciding with death, the end of the balance beam fell with an audible blow, fell on the lower limiting bar and remained there without rebound. It was established that the loss amounted to three quarters of an ounce.”

This weight loss could not have been caused by the evaporation of respiratory moisture and sweat, because it has already been established that in the case of this particular patient this occurs at a rate of one sixtieth ounce per minute, while this loss was sudden and significant – three-quarters of an ounce in a few seconds. .

Duncan McDougall

McDougall observed similar weight loss in his other patients, but the results were inconsistent. One of the patients lost weight but then regained weight, and two other patients recorded a weight loss at the time of death that increased over time. Only one patient experienced an immediate weight loss of three-quarters of an ounce, approximately 21.3 grams, which coincided with the time of death. McDougall ignored the results of the other two patients on the grounds that the scales were not finely adjusted.

McDougal then repeated his experiment with fifteen dogs. None of them had significant weight loss, which McDougall took as supporting evidence that, according to his religious doctrine, animals have no soul. While all of McDougall’s subjects were terminally ill, there is no explanation for how he got fifteen dying dogs in such a short amount of time. One can only assume that the good doctor poisoned fifteen healthy dogs for his little experiment.

MacDougall published his discovery only six years later, citing that the experiment would have to be repeated many times before any conclusion could be drawn. It was published in 1907 in the Journal of the American Society for Psychical Research and in the medical journal American Medicine. An article about the experiment also appeared in The New York Times.

After the experiment was published in American Medicine, a debate ensued between physician Augustus P. Clark and Duncan McDougall. They exchanged letters, with the first denouncing the validity of the experiment, while the other defended his position.

Clark noted that at the time of death there is a sudden increase in body temperature, as the blood stops circulating through the lungs, where it is cooled by air. This increase in body temperature will increase perspiration and moisture evaporation, which could easily explain McDougall’s missing 21 grams. This also explains why dogs don’t lose weight after death, since dogs don’t have sweat glands and cool themselves off not by sweating, but by breathing. MacDougall countered that circulation ceased at the time of death, so the skin did not heat up as the temperature rose.


August P. Clark was not the only one to criticize McDougall’s experiments. The scientific community has sharply ridiculed the doctor as a schemer. His experiments have been claimed as an example of selective reporting, as McDougall ignored most of the results. Non-fiction writer Karl Kruzelnitsky criticized the small sample size and questioned how McDougall was able to determine the exact moment of a person’s death given the technology available at the time. Because his experiments could not be replicated and his results were unreliable, McDougall’s experiment with 21 grams did not inspire much confidence from scientists of the time.

Undeterred by skepticism, McDougall moved on to the next stage of his experiments – photographing the soul at the moment when it leaves the body, without achieving any success in this. McDougall had no more breakthroughs regarding his experiments with the human soul. His very soul went to another world in 1920.
Despite being dismissed as scientific fact, McDougall’s experiment popularized the idea that the soul weighs 21 grams, and the idea has appeared in novels, songs, and films. The title of the 2003 film “21 Grams” was taken from this belief.

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