The 21 Grams Theory

On 10 April 1901, an unusual experiment was conducted in Dorchester, Massachusetts.  Dr. Duncan MacDougall was going to prove that the human soul had mass, and was therefore, measurable.

21 grams theory

Does the soul weigh 21 grams?

Dr. MacDougall conducted this experiment on six dying patients who were placed on specially made Fairbanks weight scales just prior to their deaths.  Dr. MacDougall’s intention was to weigh each body before and after death to determine any differences measured by the delicate scales.  The patients were selected based upon their imminent death.  Two patients were suffering from tuberculosis, 5 were men and one was a woman.

In the company of four other doctors, Dr. MacDougall carefully measured the weight of his first patient prior to his death.  Once the patient died, an interesting event occurred.

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.

Dr. Duncan MacDougall

The experiment continued on the next patient with the same results.  Dr. MacDougall felt he was on to something extraordinary.  A quote from the 11 March 1907 New York Times article captures the historic moment:

“ The instant life ceased the opposite scale pan fell with a suddenness that was astonishing – as if something had been suddenly lifted from the body. Immediately all the usual deductions were made for physical loss of weight, and it was discovered that there was still a full ounce of weight unaccounted for”.

All five doctors took their own measurements and compared their results.  Not all the patients lost the same weight, but they did lose something that could not be accounted for.  Unfortunately, only four of the six patient’s results could be counted due to mechanical failures or the patient dying prior to the test equipment being in place.

But what about the consistent weight loss?  Everything was taken into account, from the air in the lungs to bodily fluids.  It still could not be explained.  An interesting variation occurred on the third patient, who maintained his same weight immediately upon death.  But after one minute, he lost about an ounce of weight.  Dr. MacDougall explained this discrepancy as follows:

I believe that in this case, that of a phlegmatic man slow of thought and action, that the soul remained suspended in the body after death, during the minute that elapsed before its freedom. There is no other way of accounting for it, and it is what might be expected to happen in a man of the subject’s temperament.

Dr. Duncan MacDougall

Following the experiment and consulting with the other attending physicians, it was determined that the average weight loss of each person was ¾ of an ounce.  Dr. MacDougall concluded that a human soul weighed 21 grams.

Dr. MacDougall conducted the same experiment on 15 dogs.  The experiments showed no change in weight following their death.  MacDougall concluded that this may signify only humans have souls.

H. LaV. Twining, a physics teacher at Los Angeles Polytechnic High School, attempted the same experiment on mice in 1917.  His conclusion was in line with that of Dr. MacDougall.  There was no deviation of weight when the mice died.

Dr. MacDougall was a respected physician of Haverhill and the head of the Research Society that was conducting work in this field for six years prior to the experiment.  Although this experiment would be considered unethical in modern times, it is still a peculiarity that sparks a lot of criticism, ranging from the methodology used to various religious implications

Dr. MacDougall admitted that more research needed to be done, but following these experiments, Dr. MacDougall diverted his attention to obtaining the ability to photograph the soul as it left the human body.  Unfortunately, following his soul weight experiments, Dr. MacDougall failed to establish any further scientific breakthroughs.  Dr. Duncan MacDougal passed away in 1920.

Of Note:  A great movie titled “21 Grams” made in 2003 references Dr. MacDougall’s experiments.  Click here for more details.

References: Snopes, Dr. Duncan MacDougall on Wikipedia, A Soul’s WeightNew York Times archived article, March 11, 1907

Jim H

Jim was born and raised in Naples, Italy. He created this website in December 2009 because of his fondness for historical mysteries. Since creating the website, Historic Mysteries has grown incredibly fast and more than 3,000 people visit this site daily. Thank you for stopping by and please bookmark this site.
  • Bye evil people

    Without the air.

    • mesh

      It is quite possible that the reduction in weight could be due to empty lungs ( no breathing of air). One can notice the difference on weighing machine ( breath in and weigh and then breathe out and weigh).

      • SacraFoolMento

        The experiment took that into consideration. It describes in detail in the article… :) Try Again?

  • Beardeddude

    Did you read the article? They measured and alotted for lost air, and body fluids in the measurements. Although it cannot prove anything concrete, you have to say it is intriguing at the least. There were 4 other doctors also present for this test that did thier own measurements. I dont see how this would be unethical for todays medicine to test. It is non intrusive and does not interfere with the natural process of death.

    • Leonardo Ronaz

      Oh snap. ;]

  • TheTechnomancer

    It’s not just at that time, most Christians believe that humans are special in the way that God gave us dominion over other animals, and furthermore, humans have souls. PLEASE DONT REPLY TO THIS. WE ALL HAVE OUR OWN BELIEFS AND I DONT WANT MY EMAIL TO GET SPAM ABOUT THIS. ===DONT REPLY===

    • JooonsJoonz

      “we all have our own beliefs but only i have the right to state my opinion” how convenient christian.

  • Ravi Singh-Chumber

    As a Sikh and beliver in the soul, the whole thing sounds wrong because everything has a soul, dogs and mice too. This was probably a hoax.

  • Leonardo Ronaz

    A lot of people share a belief that the soul is made of a gelatinous fluid known as “Plasma” Although the stars in the sky are of the same material so… maybe when you die you become one of the stars??? ^^

    • Mouse

      Well, we all have plasma in us, alive or dead. It’s the fluid our red and white blood cells and platelets float in. I think you’re thinking of ectoplasim.

  • holy moly

    I have a hard time believing dogs don’t have souls. Cats on the other hand…

  • The Flobbit

    I thought the entire point of a soul was that it was not physical. Souls don’t exist on this plane.

  • tamesha

    hey love you i kiss you

  • Jorge

    Conducted on six patients, and no it wasn’t reliable.

  • Philippe Baudouin

    Hello, great documentary ! Could you give the references of the video archives used in your film ? I’d like to know it for my research. Thanks !

  • effi

    Maybe the particles in the body more active when its alive which means they move faster and the faster they move the bigger mass they have… =)

  • MavusiKenpachi

    Has anyone tried?

    • Julie


  • MavusiKenpachi

    Why do you hate science?

    • Julie


  • paendragon

    How much did the air in their lungs weigh?


    • AntiJihad Amy

      Good catch!

      • paendragon


    • Petros

      Could be mass at rest weight difference as well

      • paendragon

        But wouldn’t they weigh the same unconscious as dead, then?

        • Petros

          Not really, your heart for example still beats when unconscious therefore it has more mass…

          • paendragon

            Hm! Movement does create momentum.

  • Mouse

    When you donate your body for research you are already dead. This measurement has to be done at the time of death.