Why does Giovanni not die from Beatrice's breath (he just becomes poisonous himself) in "Rappaccinis Daughter."

Hawthorne's "" is one of those
classic stories which is worth discussing.  This is a good question with a simple
answer--Giovanni had become accustomed to the poison in small doses and was therefore immune to
its effects.

When he first arrived, he was given a room directly over the
garden and the window was open.  We know the poisons in the garden were powerful enough for
Doctor Rappaccini to wear a mask at least some of the time.  Some of that poison was no doubt
carried in the air particles Giovanni unknowingly breathed in every day. 

After he and Beatrice developed a speaking relationship, they talked mostly through
that same window overlooking the garden.  More opportunities for Giovanni's body to become
accustomed to the poison.  We know this was happening, because one day Signor Baglioni saw
Giovanni on the street and almost didn't recognize him--his coloring had become that of
Beatrice's, an almost too vivid version of itself. 

Finally, once the young
couple were spending actual time together (after conveniently being given a key to the garden),
they spent it within the confines of the garden.  This all happened slowly, of course, and in a
way which was virtually unnoticeable to either Giovanni or Beatrice.  The final understanding
dawns on Giovanni as he sees Beatrice "kill" flowers and flying insects and as he sees
his own flesh marked by the poison, as well.  If they ever had kissed, which they didn't do in
the story, it seems unlikely either would have poisoned the other.