(Duncan) MacDougall seems not to have made any more experimental breakthroughs regarding the measurement of the human soul after 1911 (at least, none considered remarkable enough to have been reported in the pages of the New York Times), and he passed away in 1920. Nonetheless, his legacy lives on in the oft-expressed maxim that the human soul weighs 21 grams. (At the moment of death, MacDougall's first test subject decreased in weight by three-fourths of an ounce, which is 21.3 grams.)
What to make of all this? MacDougall's results were flawed because the methodology used to harvest them was suspect, the sample size far too small, and the ability to measure changes in weight imprecise. For this reason, credence should not be given to the idea his experiments proved something, let alone that they measured the weight of the soul as 21 grams. His postulations on this topic are a curiousity, but nothing more.