The real doctor’s name was Henry Johnston (not Johnson). The star he wears is a reference to the Williamite star used in Orange Order symbolism. The wearing of this star tells the audience that Dr. Johnson is a Unionist whose sympathies are against the Irish rebels.
Follow this story from the beginning here.
Ballinabricky 
Did you write the story, and especially the rhyming texts, yourself? It reads like a poem 🙂
It’s a very old rebel song. I’ll have a link to a recording of it in the last episode (I just didn’t want to spoil the ending by linking it too early!).