The said jury commissioners, clerk and assistants, shall be paid for their services by the county treasurer of the several counties, such compensation as shall be fixed by the county board, upon warrants drawn by the clerk of the county board. The said jury commissioners shall be allowed a reasonable sum every year for stationery and office expenses other than salaries, which shall be paid in like manner: Provided that the said judges, or a majority of them, shall prescribe the number of assistants to be employed by said jury commissioners.