Appearance
 

A Bloodhound is a large breed of dog bred for the specific purpose of tracking human beings. Consequently, it is often used by authorities to track escaped prisoners or missing persons. It is a scenthound, famed for its ability to follow a scent hours or even days old, over long distances. Combining a keen sense of smell with a tenaciously strong tracking instinct, bloodhounds have proven their worth as the archetypal trailing dog. Bloodhounds weigh from 80 to 110 lb (36 to 50 kg) and stand 23 to 27 inches (58 to 69 cm) high at the withers. The acceptable colors for Bloodhounds are black and tan, liver and tan, or red. In the Middle Ages, they also occurred in other solid colors, including white (known as the Talbot hound). The colors appear in other breeds descended from the early Bloodhounds, however.

Bloodhounds possess an unusually large skeletal structure; most of their weight is concentrated in their bones, which are very thick for their length. The coat is typical for a scenthound: hard, and composed of fur alone, with no admixture of hair. The breed is a mellow, cheerful, affectionate dog who is nonetheless tireless in following a scent. Because of its strong tracking instinct, it can be willful, and somewhat difficult to obedience train. However, with the proper amount of time and effort, this can be achieved. Affectionate, gentle, and even-tempered, they make excellent family pets but, like any large breed, may require supervision when around small children because of the possibility of knocking them over with their bulk.

Tracking
 

The Bloodhound's physical characteristics account for its superlative ability to follow a scent trail left several days in the past. Humans constantly shed skin cells, as newer cells replace older ones. Under optimal conditions, a Bloodhound can detect as few as one or two skin cells. Odors are identified by scent receptors in a dog's nasal chambers; the larger the chambers, the greater the dog's ability to detect skin cells. The Bloodhound's nasal chambers are larger than those of most other breeds. The large and long pendent ears serve to prevent wind from scattering nearby skin cells while the dog's nose is on the ground, and the folds of wrinkled flesh under the lips and neck, called the shawl, serve to catch stray scent particles in the air or on a nearby branch as the bloodhound is scenting, reinforcing the scent in the dog's memory and nose.

The misconception persists that bloodhounds are employed in packs. While this is sometimes the case in England, in North America bloodhounds are used as solitary trackers. Bloodhounds on a trail are usually silent, and do not give voice as other scent hounds.