After due investigation, the Commissioner may license for not less than two nor more than six years, any suitable person to keep a private hospital for the mentally ill, which shall be subject to visitations from the Commissioner. A license granted hereunder shall exempt the licensee from the licensing requirements of section 1901 et seq. of this title. (Added 1967, No. 305 (Adj. Sess.), § 1, eff. Oct. 1, 1968.)