Sec. 5. The employment of a rural school supervisor under the terms of this Act shall exempt the County Superintendent from holding a teachers' institute for rural teachers;  and in all counties having a population of twenty-nine thousand, three hundred (29,300) to twenty-nine thousand, five hundred (29,500), according to the last available Federal Census, shall exempt the County Superintendent from holding a teachers' institute for teachers of independent districts with a scholastic population of less than five hundred (500);  and shall exempt the teachers of such schools of the county from attendance upon a teachers' institute, as provided for in Article 2691, Revised Civil Statutes of Texas of 1925, and as amended by the Fortieth Legislature.