Why do Injun Joe and the Dr. fight?

Injun Joe and Doc Robinson argue, and then fight, over the money he owes them for grave robbing. Their argument also enlightens the reader about Injun Joe's past grievances against the doctor.

"Five years ago you drove me away from your father's kitchen one night, when I come to ask for something to eat, and you said I warn't there for any good; and when I swore I'd get even with you if it took a hundred years, your father had me jailed for a vagrant. Did you think I'd forget. The Injun blood ain't in me for nothing. And now I've got you, and you got to settle, you know!"