Each of Dr. Heidegger's "friends" whom he invites to his house to experiment on with his fountain of youth tonic suffers from a tragic flaw or sin. Those flaws cause each to want to return to his youth, but because they have never corrected their vices, they are doomed to repeat the same mistakes. Mr. Medbourne in his youth
"had been a prosperous merchant, but had lost his all by a frantic speculation."
He loses not just the money that he invested in risky business deals, but he also lost his reputation and his happiness, which seemed to be dependent on his monetary status.
Unfortunately, when Mr. Medbourne drinks the tonic, he reverts back to his old greedy ways.