feature in "The Adventure of the Empty House" when spent bullets are recovered to be matched with a suspected murder weapon, a practice which became regular police procedure only some fifteen years after the story was published. Laura J. Snyder has examined Holmes's methods in the context of mid- to late-19th-century criminology, demonstrating that, while sometimes in advance of what official investigative departments were formally using at the time, they were based upon existing methods and techniques. For example, fingerprints were proposed to be distinct in Conan Doyle's day, and while Holmes used a thumbprint to solve a crime in "The Adventure of the Norwood Builder" (generally held to be set in 1895), the story was published in 1903, two years after Scotland Yard's fingerprint bureau opened. Though the effect of the Holmes stories on the development of forensic science has thus often been overstated, Holmes inspired future generations of forensic scientists to think scientifically and analytically. Disguises Holmes displays a strong aptitude for acting and disguise. In several stories ("The Sign of Four", "The Adventure of Charles Augustus Milverton", "The Man with the Twisted Lip", "The Adventure of the Empty House" and "A Scandal in Bohemia"), to gather evidence undercover he uses disguises so convincing that Watson fails to recognise him. In others ("The Adventure of the Dying Detective" and "A Scandal in Bohemia"), Holmes feigns injury or illness to incriminate the guilty. In the latter story, Watson says, "The stage lost a fine actor ... when [Holmes] became a specialist in crime". Guy Mankowski has said of Holmes that his ability to change his appearance to blend into any situation "helped him personify the idea of the English eccentric chameleon, in a way that prefigured the likes of David Bowie." Agents Until Watson's arrival at Baker Street, Holmes largely worked alone, only occasionally employing agents from the city's underclass. These agents included a variety of informants, such as Langdale Pike, a "human book of reference upon all matters of social scandal", and Shinwell Johnson, who acted as Holmes's "agent in the huge criminal underworld of London". The best known of Holmes's agents are a group of street children he called "the Baker Street Irregulars". Combat Pistols Holmes and Watson often carry pistols with them to confront criminals—in Watson's case, his old service weapon (probably a Mark III Adams revolver, issued to British troops during the 1870s). Holmes and