The Bloodhound is a large scent hound, originally bred for hunting deer, wild boar and, since the Middle Ages, for tracking people. Bloat took 34% of the animals, making it the most common cause of death in Bloodhounds. The second leading cause of death in the study was cancer, at 27%; this percentage is similar to other breeds, but the median age of death was unusually young (median of about 8 years). In a 2013 survey, the average age at death for 14 Bloodhounds was 8.25 years. To De Fouilloux the 'pure black' were the best of this mixed breed. Both writers thought them only useful as leash hounds. Descriptions of the desirable physical qualities of a hunting hound go back to Medieval books on hunting. All dogs used in the hunting field were 'gentle', that is of good breeding (not necessarily pure breeding), and parents were carefully chosen to maintain and improve conformation.