Section 938 - County detective in counties of Bronx and Kings, County detectives are hereby empowered, under the direction of the district attorney by whom appointed, to preserve order, to examine all papers and processes issued from such offices, to serve all papers and processes issued from such office, to examine all bench warrants and orders of arrest in criminal cases, and to perform such other duties as may from time to time be required of them by such district attorneySuch officers may be authorized to act as deputy sheriffs by the sheriff of the city of New York to assist in preserving the peace. Such officers shall hold office during the pleasure of the district attorney.