From and after the passage of this Act in all counties of the State of Texas which have a population of not less than seventy-seven thousand (77,000) and not more than seventy-seven thousand, six hundred (77,600), and in all counties of the State of Texas which have a population of not less than fifty-one thousand, seven hundred and seventy (51,770) and not more than fifty-one thousand, eight hundred (51,800), according to the last preceding Federal Census, the salary of the County Superintendent of Public Instruction shall be Thirty-six Hundred Dollars ($3600) per annum; and in all counties of the State of Texas which have a population of not less than twelve thousand, one hundred and ninety (12,190) and not more than twelve thousand, two hundred (12,200), according to the last preceding Federal Census, the salary of the County Superintendent of Public Instruction shall be Three Thousand Dollars ($3,000) per annum; and in all counties of the State of Texas which have a population of not less than thirteen thousand, four hundred (13,400) and not more than thirteen thousand, five hundred (13,500), according to the last preceding Federal Census, the salary of the County Superintendent of Public Instruction shall be Twenty-eight Hundred Dollars ($2800) per annum; and in all counties of the State of Texas which have a population of not less than twenty-seven thousand, five hundred (27,500) and not more than twenty-seven thousand, six hundred (27,600), according to the last preceding Federal Census, the salary of the County Superintendent of Public Instruction shall be Twenty-four Hundred Dollars ($2400) per annum, to be paid in accordance with and in the manner as provided by the general law governing the maintenance of the office of County Superintendent, as provided in Article 2700, Revised Civil Statutes, 1925.