In 1901, a doctor by the name of Duncan MacDougall made a discovery that he thought would revolutionize science—a way to measure the mass of the human soul. While it may seem crazy, the loss of mass that was experienced by his patients is documented as real.
MacDougall began by recruiting participants who were in their last few days of dying from tuberculosis. He took his six participants, laid their beds on a large scale, and closely monitored their weight before and immediately following their passing. What he discovered was astonishing: The subjects lost, on average, 21 grams (0.75 oz) in body weight when they died. With no other possible explanation, MacDougall concluded that this must be the exact weight of the human soul.
He claims that the weight drop couldn’t be a result of evaporation, sweat, or loss of bowels because of how rapidly the drop occurred. He also claimed that it could not have been loss of air in the lungs, because when he attempted to force air back into the patients, the scale didn’t change. His colleague and critic, Augustus Clarke, believed the weight change to be caused by the sudden rise in body temperature as the blood stops being cooled and circulated—but Dr. MacDougall maintained his theory, testing it on dogs as well as other animals and finding no weight drop as he did in humans. MacDougall believed that his hypothesis should be put up to more testing due to his small sample size, but his research ended when he abruptly died in 1920.