The state is authorized to become indebted and to issue interest bearing bonds, in addition to those heretofore authorized and sold, in an aggregate principal amount not exceeding $3,000,000. The proceeds derived from the sale of said bonds shall be used solely for the purpose of paying the expenses incurred in the sale and issuance thereof and for the construction and equipment of a hospital building to constitute a part of the University of Alabama Medical Center, and to be used for the care and treatment of mental patients and for training of medical students in the field of mental illness. Said bonds shall be sold only at a duly advertised public sale or sales, upon sealed bids or at auction, to the bidder whose bid reflects the lowest net interest cost to the state for the bonds offered for sale, and shall be sold at not less than their face value plus accrued interest thereon. Said bonds shall be direct general obligations of the state and for the prompt and faithful payment of the principal thereof and interest thereon the full faith and credit of the state are hereby irrevocably pledged. In addition thereto, there is hereby specifically and irrevocably pledged for payment of the principal of and interest on said bonds, pro rata and without priority of one bond over another by reason of prior issuance or otherwise, so much as may be necessary for said purpose of those portions of the state taxes on the sale of spirituous or vinous liquors and of the state license taxes on those selling, storing or receiving for distribution malt or brewed beverages that are required by law on the date of the adoption of this amendment to be paid into the Alabama special mental health fund. The said special pledge shall create a charge on the tax proceeds herein specially pledged prior to all other charges or expenses for mental health purposes or any other purposes whatsoever. The bonds issued under this amendment and the income therefrom shall be exempt from all taxation in the state of Alabama. The legislature shall adopt appropriate enabling legislation to carry out the intent and purpose of this amendment.