Each bond or note and coupon shall be cancelled when (i) it is paid, or (ii) it is acquired by the issuing unit in any manner other than purchase for investment. A full report of the cancellation of all bonds, notes, and coupons shall be made to the secretary on forms provided by the Commission. (1931, c. 60, s. 27; 1939, c. 356; 1971, c. 780, s. 1.)