Michigan Compiled Laws, Chapter 51. Sheriffs § 51.73

Sec. 73. Every appointment of an under sheriff, or of a deputy sheriff, and every revocation thereof, shall be in writing under the hand of the sheriff, and shall be filed and recorded in the office of the clerk of the county; and every such under sheriff or deputy shall, before he enters upon the duties of his office, take the oath prescribed by the twelfth article of the constitution  1 of this state. But this section shall not extend to any person who may be deputed by and sheriff to do a particular act only.