In 1901, Dr. Duncan MacDougall decided to carry out an experiment on six of his patients, all of whom were dying of tuberculosis.
The reason for MacDougall's experiment was to prove his hypothesis that the human soul has mass and that this mass is lost when the soul leaves the body.
McDougall's theory was popularized in the 2003 movie, 21 Grams, therefore many of the general public assume that the movie, 21 Grams, is the true source of the information - they don't realize that the experiment genuinely was carried out back in 1901. As a result of his experiment, MacDougall concluded that the human soul weighs a total of 21 grams, based on the average loss of mass in his six patients within moments of dying. However, further experiments on other animals including dogs, mice and sheep failed to show similar results.
Unexpectedly for MacDougall, his experiments with animals indicated that there was actually an increase of mass in sheep after death, which disappeared shortly after and no increase or decrease of mass in dogs after death. In self-assurance of his hypothesis about the human soul, MacDougall believed that the lack of change of mass in dogs after dying must have been an indication that dogs have no soul.
Even more peculiarly, MacDougall believed that the increase of mass in sheep after dying, before dissipating, was an indication of some kind of "soul portal" opening up to carry the soul away. It was later speculated that MacDougall may have been guilty of poisoning dogs in order to carry out his experiments, though this was never proven nor disproven.
MacDougall is not the only person who has supported the theory that the human soul has mass, Sir William Crooke also believed in the theory.
[ Image: Geralt at Pixabay - Public Domain - https://pixabay.com/en/face-soul-head-smoke-light-sad-622904/ ]