He wants to study the effects of water from the fountain of youth on the human body.
Explanation:
In the experiment, the doctor learns that the human in his last trance will commit the same mistakes even if they have a second chance to be young and fix their life. Instead of regret, they will be obsessed with the fantasy of being pretty, strong and desirable. That's why Dr Heidegger's didn't want to drink and will never because he watched the effect on his friends
