The commanding officers of regiments and battalions not part of regiments shall appoint and warrant the noncommissioned staff officers of their respective regiments or battalions, and they shall, in their discretion, warrant the noncommissioned officers of the companies of their respective regiments and battalions from the members thereof, upon the written nomination of the commanding officers of the companies, respectively. In troop, battery, and companies not part of a regiment or battalion and in the hospital corps the noncommissioned officers shall be warranted by the commanding officer of the brigade, in his discretion, from the members thereof, upon the written nomination of the commanding officer of the troop, battery, company, or hospital corps. The officer warranting a noncommissioned officer shall have power to reduce to the ranks, for good and sufficient reasons, the noncommissioned officers named in this section, but such as were enlisted as noncommissioned officers shall be discharged. Noncommissioned officers who shall be dropped vacate their positions.