In 1901, Massachusetts surgeon Dr. Duncan MacDougall attempted to prove the existence of the soul by weighing a person before, and right after, death. He hacked an industrial beam scale so that it could be attached to a hospital bed. Then, he began to seek out a subject in the terminally ill patients at the hospital. First up was a man dying of tuberculosis. According to MacDougall, “The instant life ceased, the opposite scale pan fell with a suddenness that was astonishing – as if something had been lifted from the body.” Apparently, 21 grams was missing from his body. MacDougall reproduced the experiment several more times. The physician's work has become a classic tale that, of course, is still widely cited by philosophers, skeptics, and "believers." And yes, it's MacDougall's experiments that inspired the film 21 Grams too. Fortean Times weighs the truths, half-truths, and unknowns of "the strange deathbed experiment of Dr. MacDougall." From FT:




Deducing exactly what went on in MacDougall’s laboratory after more than a century has passed is no easy task, but a possible insight comes from some written correspondence between MacDougall and Richard Hodgson. These letters (which were later published by the American Society of Psychical Research) start in November 1901, after MacDougall’s first experiment, and continue until May 1902, when the entire project was halted. They contain a full description of MacDougall’s methods, results and the circumstances of all six patients which, when compared with his American Medicine paper, offer some clues to the solution of this mystery.

MacDougall’s letters make it plain that, with the exception of the first patient, all the experiments were beset with problems that may be broadly divided into one of two categories. The first problem was in ascert­aining the exact time of death, an issue that appears to affect patients two, three and six. MacDougall acknowledged this with the second patient, where the period of uncertainty lasted for 15 minutes, but with patient three it is only in his letters that we learn of “a jarring of the scales” made while trying to determine “whether or not the heart had ceased to beat”. Patient six was excluded for other reasons (see below), but in his letters MacDougall remarks that “I am inclined to believe that he passed away while I was adjusting the beam”, which again suggests uncertainty as to the exact moment of death.



The second issue was a problem relating to the measuring equipment itself, which MacDougall himself cited as a reason for voiding the results of patients four and six. However, with the fifth patient the measured drop in weight at death was later followed by an evident malfunction, as the scales could not afterwards be made to re-balance themselves correctly. In any object­ive experiment this uncertainty would have voided the result, but at no point does MacDougall question the reliability of his set-up. Thus, of the six patients, just one (the first) appears to have been measured without mishap, but repeated troubles with the equipment and with determining the moment of death perhaps casts doubt on even these results. Thus, rather than trying to find a physical cause for the loss of weight at death, it is conceivable that there was no loss of weight at all, or that it might not have coincided with the moment of death. Only a complete retrial with human patients will answer these questions, and that has so far not been forthcoming