It shall be the duty of the judges of the several district courts, in all cases, both civil and criminal, to reduce their charges or instructions to the jury to writing, before giving the same to the jury, unless the so giving of the same is waived by the counsel in the case in open court, and so entered in the record of said case; and either party may request instructions to the jury on points of law, which shall be given or refused by the court. All instructions asked shall be in writing.