I know I have posted this somwhere before but here goes
Bloody or 's blood is short for God's Blood And damn or darn is again short for God's damnation.
Oaths that took the Lords name in vain were in the time of Catholisism in the uk punished as a heresy and when the Protestant religion took over it was punished as a civil crime.
some of the punishment was rather extreme including having your tounge bored through with a hot iron.
dave a sad re-enactor