In 1901 a doctor named Duncan MacDougall conducted an interesting experiment to find if the human soul had mass. The experiment was conducted on six dying patients (five men and one woman) placed on a specially made weight just prior to their deaths. 5 were men and one was a woman.
When death occurred the weight dropped on an average with 21 grams; some more and some less, but all lost weight. The conclusion of Dr Duncan MacDougall were that the soul weighs 21 grams. After his death nobody have intended to investigate further this 21 gram theory.
On mice and on dogs the weight did not change. The conclusion for the researchers were that they did not have a soul.