1. Gustafsson, B., Acta Path. Microbiol. Scand., 73, 1 (1948).
2. Davey, D. G., Laboratory Animals Centre Coll. Papers, 8, 17 (1959).
3. Wheeler, S. M., J. Animal Tech. Assoc., 14, 23 (1963).
4. Berdjis, C. C., Dis. Chest., 37, 621 (1960).
5. Laboratory Animals Centre Pamphlet (August 1963).