What do the four guests decide to do at the end of the story?
The moral of "Dr. Heidegger's Experiment" is ambiguous. Dr. Heidegger seems to decide that old age is preferable to youth because age brings understanding and discretion. His four guests, however, are not concerned about gaining wisdom. They have had the opportunity to experience the undeniable advantages of youth again, and they all feel that the advantages outweigh the disadvantages. Dr. Heidegger has understood that youth is a period of "delirium." He tells his guests:
"...if the fountain gushed at my very doorstep, I would not stoop to bathe my lips in it--no, though its delirium were for years instead of moments. Such is the lesson ye have taught me!"
But the doctor's four friends had taught no such lesson to themselves. They resolved forthwith to make a pilgrimage to Florida, and quaff at morning, noon, and night, from the Fountain of Youth."
Youth obviously has many advantages. Young people have good looks, energy, vitality, and seemingly infinite time to live. But they lack moderation and discretion. And of course they lack experience. They have many hard lessons to learn in the years ahead of them, and most of them do not realize this is the case. Most have great expectations--but life never turns out the way young people want it to or dream it will or believe it should. Charles Dickens dramatized that truth in his best novel Great Expectations. Dr. Heidegger realizes from his experiment that regaining youth is not worth it if it means giving up almost everything one has learned through the vicissitudes of surviving to old age.
As the Bible puts it:
With the ancient is wisdom; and in length of days understanding.
Dr. Heidegger invites four elderly people to his home. While they are there he claims that the liquid in a particular vase at his home is water from the mythical Fountain of Youth. He would like their help in an experiment: they drink the water, he sits back andobserves. The guests are clearly sceptical, but they agree. Before they drink, Dr. Heidegger warns them not to make the same mistakes as they did when first young. The guests drink, and they believe they have grown young again. The guests act like fools, and the three men end up wrestling each other for the Widow's attention. In their roughhousing they knock over the vase, which spills the liquid all over the floor.
As the effects of the potion to wear off, and the four guests find that they are old again. Dr. Heidegger does not regret the spilled elixir; he has learned his lesson by watching his guests, and would not drink the water for anything. The guests, however, have learned nothing, and decide to travel to Forida where they will drink from the fountain of youth.