Section 4. The commissioner, or his examiners or such others of his assistants as he may designate, may summon the trustees, officers or agents of a bank, or any other witnesses, and examine them relative to the affairs, transactions and condition of the bank, and, for that purpose, may administer oaths. Whoever, without justifiable cause, refuses to appear and testify when so required or obstructs the person making such examination in the performance of his duty, shall be punished by a fine of not more than one thousand dollars or by imprisonment for not more than one year.