If, at the time of impaneling the grand jury in any circuit court, the district attorney be absent or unable to perform his duties or, if after impaneling of the grand jury, the district attorney be absent or unable to perform his duties or be disqualified, the court shall forthwith appoint some attorney at law to act for the state in the place of the district attorney during his absence or inability or disqualification, and the person appointed shall have the power to discharge all the duties of the office during the absence or inability or disqualification of the district attorney, and shall receive a reasonable compensation for his services, to be allowed by the court and certified to the auditor, who shall issue his warrant therefor. Such allowance shall be deducted from the salary of the district attorney, and shall not exceed the amount of the salary of the district attorney for the number of days allotted by law for the term of the court at which such appointees shall act.