Section 141. Whoever violates any provision of sections one hundred and thirty-seven, one hundred and thirty-seven A, one hundred and thirty-seven B, or one hundred and thirty-eight shall forfeit not less than twenty-five dollars, which shall be paid, if the dog was kept in any town in Suffolk county, to the treasurer of the town, or, if kept in any other county, to the treasurer thereof. If the dog as to which such violation occurs was unlicensed at the time of such violation, the court shall impose the forfeiture provided herein.