The state auditor shall levy each year on all taxable property within the state whatever tax may be necessary to produce an amount sufficient, with all money then and theretofore transferred under section 167.51, and all income from the investment thereof, to pay the entire amount of principal and interest which is then due or is to become due within the then ensuing year and to and including July 1 of the second ensuing year, on Minnesota trunk highway bonds heretofore issued and all such bonds hereafter issued pursuant to section 167.50. Such tax shall be subject to no limitation of rate or amount until all such bonds and all interest thereon are fully paid. The proceeds of such taxes are appropriated and credited to the state bond fund, and the principal and interest of said bonds are payable from the proceeds of such taxes, and the whole thereof, or so much thereof as may be necessary, is appropriated for such payments. If at any time there is insufficient money from the proceeds of the taxes provided for herein to pay the principal and interest when due on such bonds, then such principal and interest shall be paid out of the general fund in the state treasury, and the amount necessary therefor is hereby appropriated. The general fund shall be reimbursed from the proceeds of said taxes when received.