In counties having a population of not less than seventy-seven thousand (77,000), and not more than seventy-seven thousand, six hundred (77,600), and in counties having a population of not less than fifteen thousand, five hundred and fifty (15,550), and not more than fifteen thousand, five hundred and sixty (15,560), and in counties having a population of not less than nineteen thousand, one hundred and thirty (19,130) and not more than nineteen thousand, three hundred (19,300); and in counties having a population of not less than thirty-four thousand, six hundred (34,600) and not more than thirty-four thousand, seven hundred (34,700), according to the last preceding Federal Census, the County Boards of Trustees may make such provisions as they deem necessary for office and traveling expenses of the County Superintendent of Public Instruction, and any assistant he may have; provided that the amount of such expenditures for office and traveling expenses shall not exceed the sum of Six Hundred Dollars ($600) per annum. The amount allowed shall be paid in the manner and in accordance with now existing laws governing the maintenance of the office of the County Superintendent.