...he was doing a breath hydrogen test. If you know the amount of hydrogen someone is exhaling orally, it's a simple matter to extrapolate the amount they're exhaling rectally. This is because a fixed percentage of hydrogen produced in the colon is absorbed into the blood and, and when it reaches the lungs, exhaled. The breath hydrogen test has given flatus researchers a simple, consistent measure of gas production that does not require the subject to fart into a balloon.
What sort of person experimentally infests a child with maggots? A confident sort, certainly. A maverick. Someone comfortable with the unpretty facts of biology. Someone who is perhaps himself an unpretty fact of biology.
Weightlessness is like heroin, or how I imagine heroin must be. You try it once, and when it's over, all you can think about is how much you want to do it again. But apparently the thrill wears off.