Such a donation, when received by a town, shall, unless otherwise directed by the donor, be paid to the town treasurer; and the income therefrom shall be paid by such treasurer to such person as the selectmen may annually appoint to receive and expend such income. The person so appointed shall give a bond to the town for such sum as the selectmen may fix, with surety to their satisfaction, conditioned for the faithful performance of his duties; and thereupon such person shall expend such income pursuant to the terms of the instrument or declaration of trust regulating the use thereof, and, when no specific direction has been made by the donor relative to the expenditure of such income, or when the purpose specified is incapable of performance, or when there is a surplus of income after the directions of the trust have been fully complied with and performed, he shall expend the same wholly or in part for the general care or improvement of the cemeteries and burial lots or of private lots within such cemeteries in such town.