The state of Alabama is authorized to become indebted and to sell and issue interest-bearing bonds, in addition to all other bonds of the state, in an aggregate principal amount not exceeding $15,000,000. 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 acquisition, construction and improvement of mental health facilities, including (a) improvements to the existing state hospitals for the mentally ill known as Bryce and Searcy hospitals and to the existing state facilities for treatment and care of the mentally retarded known as Partlow School, for which improvements not exceeding $3,000,000 of the proceeds from the said bonds may be used, (b) acquisition by construction and otherwise of one or more new state facilities and regional centers, or either, for treatment and care of the mentally retarded, for which purpose not exceeding $9,000,000 of the proceeds from the said bonds may be used, and (c) acquisition by construction and otherwise of regional and community-based mental health centers and regional and community-based centers for treatment and care of the mentally retarded, for which purpose not exceeding $3,000,000 of the proceeds from the said bonds may be used; provided, that bond proceeds may be used for a center referred to in the foregoing clause (c) only if a portion of the cost of that center is to be paid out of funds supplied by federal grant or by contribution of local political subdivisions or other local sources, or by both federal grant and such contribution. The improvement of a facility shall be deemed to include the renovation, modernization, remodeling, and equipment thereof and the construction of additions thereto; and the construction of a facility shall be deemed to include the acquisition of real estate sites and equipment therefor. 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 specially 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, that portion of an additional privilege and license tax on the sale, storage, use, consumption, or delivery of cigarettes, levied by an act adopted at the 1967 regular session of the legislature of Alabama, that was appropriated in the said act to the purpose of acquiring and constructing mental health facilities in the state. The said special pledge shall create a charge on the tax proceeds herein specially pledged prior to all other charges or expenses for any purpose. The bonds issued under this amendment and the income therefrom shall be exempt from all taxation in the state. The legislature shall adopt appropriate enabling legislation to carry out the intent and purpose of this amendment.