Green’s Dictionary of Slang

Cain n.

In exclamations

by Cain!

(US) a mild, euph. oath, by hell!

[US]A. Peirce Rebelliad 40: I swear by Hadley, and by Cain, You ne’er shall taste my wine again [DA].
H.J. Conway Hiram Hireout 11: Sweet as a butterfly’s breath, by Cain [DA].