§ 221. Duty of railroad commissioners. It shall be the duty of the railroad commissioners of the town, any part of whose territory shall have been detached as aforesaid, to render a true statement to the board of supervisors, as required by law, of the amount necessary to pay the proportionate share belonging to the territory detached from their town, which may be then coming due, and the board of supervisors shall add such proportionate share to the sums to be collected from the town so formed, or to the part which shall have been detached from a town and added to another town, to be collected as prescribed by law.