In a challenge for implied bias, one or more of the causes stated in the second preceding section¹ must be alleged. In a challenge for actual bias, the cause stated in the second subdivision of the third preceding section² must be alleged; but no person shall be disqualified as a juror by reason of having formed or expressed an opinion upon the matter or cause to be submitted to such jury, founded upon rumor, statements in public journals, or common notoriety, provided it appears to the court, upon his declaration, under oath or otherwise, that he can and will, notwithstanding such opinion, act impartially and fairly upon the matters to be submitted to him. The challenge may be oral, but must be entered upon the minutes of the court.