1991
January January 1; 68 (1): 1 - 318	February February 1; 68 (2): 319 - 620	March March 1; 68 (3): 621 - 904
April April 1; 68 (4): 905 - 1178	May May 1; 68 (5): 1179 - 1491	June June 1; 68 (6): 1495 - 1772
July July 1; 69 (1): 2 - 255	August August 1; 69 (2): 257 - 558	September September 1; 69 (3): 561 - 885
October October 1; 69 (4): 887 - 1169	November November 1; 69 (5): 1171 - 1425	December December 1; 69 (6): 1427 - 1644