Except as otherwise herein provided, no trustee and no employee of the board of trustees shall have any personal interest in the gains or profits of any investment made by the board; nor shall any trustee or employee of the board, directly or indirectly, for such trustee or employee or as an agent, in any manner for such trustee or employee or as an agent, in any manner use the same except to make such current and necessary payments as are authorized by the board; nor shall any trustee or employee of the board become an endorser or surety, or in any manner an obligor, for money loaned to or borrowed from the board.