Green’s Dictionary of Slang

blood! excl.

a mild excl.

1704		‘Helter Skelter’ in N. Ward Poems on Divers Subjects (1706) 158: Blood, Sir, for all you talk so big, / I say, you’re but a Canting Whig.
1725		View of London & Westminster (2nd part) 4: [A]ny other useful Expletive, such as Blood, Hell, and that excellent English particle Zounds.
1770		D. Gunston (ed.) Jemmy Twitcher’s Jests 66: Blood! says he, you’re so fat, a body can’t feel what you have got [i.e. a whore’s vagina].