Before any mutual savings bank shall be authorized to do business, its incorporators shall create an expense fund from which the expense of organizing such bank and its operating expenses may be paid, until such time as its earnings are sufficient to pay its operating expenses in addition to such dividends as may be declared and credited to its depositors from its earnings. The incorporators shall deposit to the credit of such savings bank in cash as an expense fund the sum of five thousand dollars. They shall also enter into such an agreement or undertaking with the director as trustee for the depositors with the savings bank as he or she may require to make such further contributions in cash to the expense fund as may be necessary to pay its operating expenses until such time as it can pay them from its earnings, in addition to such dividends as may be declared and credited to its depositors. Such agreement or undertaking shall fix the maximum liability assumed thereby which shall be a reasonable amount approved by the director and the same shall be secured to his or her satisfaction, which security in his or her discretion may be by a surety bond executed by a domestic or foreign corporation authorized to transact within this state the business of surety. The agreement or undertaking and security shall be filed in the office of the director. Such agreement or undertaking and such security need not be made or furnished unless the director shall require the same. The amounts contributed to the expense fund of said savings bank by the incorporators or trustees shall not constitute a liability of the savings bank except as hereinafter provided.