In the early 20th century, an American doctor named Duncan McDougall tried to scientifically prove the existence of the soul. He went on the principle that if the soul really exist, it must have a material basis, and therefore weight. To be sure, McDougall saw only solution: Weigh a man to die, before and after his death. He started his macabre business in 1900, after a center for tuberculosis has authorized to carry on his experience of dying patients. The bed of the first subject was placed on a large scale, and when the dying man drew his last breath, MacDougall noted a loss of 21 grams (three quarters of an ounce) before and after death. Since there was no biological explanations for this difference, the doctor deduced that 21 grams necessarily correspond to the weight of the soul. MacDougall repeated the experiment five times and obtained similar results, reinforcing the idea that the theory was proven. Subsequently, he reproduced the operation of 15 dogs, but with...