In 1901, Dr. McDougall tried to prove through a test that the soul weighed 21 grams. Moreover, he also tries to prove that humans have souls, other animals do not.

His tests required all patients who would move very little at the time of death. Six dying people were selected, four tuberculosis patients, one diabetic, one unknown disease. Before they die, they are lifted on a weighing machine.

After testing humans, he also tested fifteen dogs. He did not get a dog suitable for his test, the idea is that he fed the dogs poison.

Results:

A person loses about 21 grams of weight at the time of death. One loses weight at first but then gains weight. The two lost weight at the time of death, but later lost more weight. He dropped the experiment data himself due to test errors.

Dogs have not been seen to lose much weight.

Sweat under normal conditions has been excluded from McDougall's test. As McDougall lay on the machine and let out a sigh, there was no change in weight. So the weight of the air that is blown out at the time of death is slightly captured.

Explanation:

Physician Augustus Clark explains McDougall's test: Lungs stop working at the time of death, so the body's cooling system fails. So the amount of sweat increases at the time of death, from which comes the calculation of 21 grams.

Dogs do not have sweat glands because they do not have a soul on their foreheads.

Moreover, McDougall's experiments were not acceptable to the scientific community because of individual data, experiments on only six people, and the omission of two data on them.

https://www.snopes.com/fact-check/weight-of-the-soul/

https://en.m.wikipedia.org/wiki/21_grams_experiment

http://rationallyspeaking.blogspot.com/2007/03/does-soul-weigh-21-grams.html?m=1