All fees except building fees shall be held by the board of regents as a revolving fund and expended for the purposes for which collected and be accounted for in accordance with law: PROVIDED, That the board of regents shall have authority to place in a separate fund or funds any or all fees or rentals exacted for the use of facilities of any dormitory, hospital, or infirmary building, and the board of regents shall have authority to pledge any or all such fees for the retirement of any bonds that may be issued for the construction of such dormitory, hospital, or infirmary building.