E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Figuratively, one who follows up an enemy with pertinacity. Bloodhounds used to be employed for tracking wounded game by the blood spilt; subsequently they were employed for tracking criminals and slaves who had made their escape, and were hunters of blood, not hunters by blood. The most noted breeds are the African, Cuban, and English.