That all pensions provided by this act [23-1-11 N.M. Stat. Ann.] shall be payable solely out of the income or current fund of the institution paying such pensions derived from the renting of lands of such institution donated by the United States of America, over and above such portion of such current income as may be necessary to service any bond issue of such institution heretofore lawfully issued, and no part of such pensions shall be paid out of the permanent fund of such institution, nor out of funds raised by general taxation.