In the late 19th and early 20th century the paradigm of the natural sciences, especially in regards to humans, underwent a massive shift. The Darwinian theory of evolution first proposed in Charles Darwin's Origin of Species was later applied to mankind in his other seminal work The Descent of Man in 1871. The idea that humanity was not something divinely made and apart from the rest of creation caused a massive debate in the scientific and medical community. Many scientists, still vehement believing that humanity was indeed special, tried to prove that humankind was indeed something apart from the animal kingdom. The co-discoverer of evolution by natural selection, Alfred Russell Wallace was among them, and the spiritualist movement of the late 19th and early 20th century attracted many to the pursuit of proving there was a divine spark to the human being. In America especially many people sought to prove that this spark, the human soul, could be quantified and measured. One such man was a medical doctor named Duncan MacDougall.
MacDougall came up with the idea that the soul may have mass, and as such would have weight. He proposed that if he could use very sensitive scales, he could measure the difference in weight caused by a departing soul on a dying human being. The problem of finding people near death was a simple in 1901. MacDougall was able to get the cooperation of a Tuberculosis hospital in his experiments. In the days before antibiotics the bacterial lung infection commonly known as "consumption" was a death sentence. It was also a disease that exhibited clear signs when the patient was just a short time away from expiring. At the first signs of an impending death the patients bed was transferred to his scales. Over the course of nearly half a dozen deaths he measured a decrease in weight averaged from 16 grams to 29 grams at the moment of death with the first patient losing 21 grams. As a control he later replicated the experiment by using dogs, which exhibited no change in weight at death. This backed his hypothesis that humanity is special because we have a soul and are something apart from the animal kingdom.
His experiments made the national papers of the day and his results were indeed published by the Society of Psychical Research. This society based in the U.K. with an American branch were the first scientifically minded parapsychologists. They counted among their ranks at the turn of the century such notable members as Alfred Russell Wallace, Sir Arthur Conan Doyle(Author of Sherlock Holmes), Louis Carroll(Author of Alice in Wonderland), Arthur Balfour(Prime Minister of Great Britain), William James(American philosopher), and many professors and social elites. It was also credible enough at the time to be published in journal American Medicine. Only in later years was the work of MacDougall seriously questioned. Challengers to his experiments mainly criticize him for having such a small pool of patients to work with. They assert more than half a dozen successful measurements would be needed to give validity to the hypothesis that the soul has mass and weight. Also critics of the time argue that the scales used in 1901 were not reliable enough to accurately measure such a small amount of weight successfully and reliably.