For the faithful and prompt payment of all interest and principal of said bonds as and when the same shall mature according to the tenor thereof, the issue thereof shall constitute an irrevocable pledge by said regents of so much of each year’s income from the permanent fund of the New Mexico school of mines [New Mexico institute of mining and technology] in the hands of the treasurer of this state, as shall be necessary to provide the “interest and retirement fund” herein mentioned, for the ensuing year, and to at all times fully and faithfully keep the same in not less than the amount necessary to pay the interest and principal maturing as aforesaid; and in addition thereto the issue of said bonds shall constitute an irrevocable pledge by said regents of so much of each year’s income from the income and current fund derived from the lease of such of its lands as remain unsold, as may be necessary to fully protect the “interest and retirement fund” for the ensuing year, and to keep the same at all times in proper amount as herein provided. Whenever bonds are issued under the authority of this act [21-11-15, 21-11-16, 21-11-18 to 21-11-26 N.M. Stat. Ann.] for the purpose of acquiring lands and buildings for use as a branch of said New Mexico school of mines [institute] and said branch is operated under contracts which produce revenue as rentals, use charges, or otherwise, the regents shall, in addition to the income from the permanent fund and the income and current fund derived from the lease of such of its lands as remain unsold, have power to pledge irrevocably as security for the principal and interest on said bonds the entire rentals, use charges or other revenues derived from the contracts under which said branch is operated.