Whenever any ticket is sold and is not wholly used by the purchaser, it shall be the duty of the carrier selling such ticket to redeem it or the unused portion thereof at the price paid for it, or in such manner and at such price as the Commission shall prescribe by regulation. (1891, c. 290; 1893, c. 249; 1895, c. 83, ss. 2, 3; 1897, c. 418; Rev., s. 2627; C.S., s. 3503; 1963, c. 1165, s. 1.)