If the maximum rate of taxation for the various purposes mentioned in the budget, for which the county may levy taxes, together with the estimated amount of the revenues of the county for the ensuing year, exclusive of those derived from taxation does not equal the total amount mentioned in the budget, or amendment thereof, the county shall reduce, proportionately, the several funds mentioned in the budget, except that the items for bonds, interest on bonds, salaries, and other items, the charges for which are fixed by law, shall remain at the full amount that the law requires.